SSB Antenna theory
This tries to explain how short SSB antennas operate and why.
The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can’t have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. Also a lot of people think that the antenna has to be resonant in order to radiate well. That is also far from true. Using a coil to cancel out the reactance of the antenna forms a resonant circuit with the antenna which must be done in order to get power to the antenna. This is a different thing than the antenna being resonant itself. But the antenna itself will perform the same whether it is resonant or not. The problem is getting power to the antenna as you will see below. CURRENT DISTRIBUTION With a full quarter wave length antenna the current distribution on the antenna is more like a sine wave curve. Larger at the bottom and tapering slowly as you go up the antenna. With an antenna shorter than a quarter wave length the current is still maximum at the bottom feed point and smallest at the top. However the shape of the distribution is different. With a short base loaded antenna the current distribution is about linear. In other words it drops in direct proportion to the length of the antenna. With center loading or top hat loading the current distribution is "pushed up" the antenna. It has a higher almost constant current at the lower part of the antenna and it drops off very fast at the top. RADIATION RESISTANCE Current distribution on the antenna determines radiation resistance. Radiation resistance determines efficiency of the antenna system. The higher the radiation resistance the higher the efficiency of the system. With a more constant current distribution that center loading gives over base loading, the radiation resistance is greater on the antenna. This allows more power to be put into the antenna to radiate. Radiation resistance is not to be confused with feed point resistance. "Radiation resistance is defined as the resistance that would dissipate the same amount of power that is radiated by the antenna." As an antenna is made shorter (less than a quarter wave length) the radiation resistance drops. As radiation resistance drops you must increase the current to maintain the same amount of power to radiate. (OHMS LAW) REACTANCE Note that the larger a capacitor is the less reactance it has. The larger an inductor (coil) is the more reactance it has. A short antenna looks like a capacitor and like any capacitor it has capacitive reactance. That reactance is AC resistance. In order to get power into that antenna you must have an equal amount of inductive reactance in the circuit to cancel out the capacitive reactance. When the two are equal the circuit is said to be resonant and purely resistive. Note that when adding the inductance it changes nothing about the antenna itself. Only the reactance / impedance seen at the feed point which is the transmitter end of the coil. The shorter the antenna (less capacitance presented) the higher the capacitive reactance and thus the larger the coil required to cancel it. This means more wire in the coil. The more wire in the coil the more resistance the coil will have. (not to be confused with reactance) The more resistance it has the more loss it will have. It gets worse, because as the antenna gets shorter its radiation resistance gets smaller as the coil resistance is getting larger. The coil resistance can be 10 times or higher in resistance than the radiation resistance of the antenna. Because they are in series the same current that flows in the antenna also flows in the coil. The coil will therefore absorb most of the power. (ohms law again) By center loading the antenna rather than base loading it the current distribution is shifted in the antenna and that increases the radiation resistance of the antenna. However it is not a free lunch. The higher up you raise the coil on the antenna the more coil is required. This increases coil loss again. But the radiation resistance of the antenna goes up faster in proportion to the coil resistance so you end up with less system loss. CURRENT IN THE ANTENNA, VOLTAGE ON THE COIL When a short antenna is used some think that the current requirement is less rather than more for the antenna. This is related to the fact that the voltage at the coil-antenna junction (output terminal on your tuner) is much higher with a short antenna. Therefore the thought is "if the voltage is higher the current must be lower". Well it isn’t! The reason the voltage is so high is because of the high inductive reactance of the coil in the tuner. Because the inductive reactance is high (lots of coil) the voltage goes high at that point. Here are some numbers to illustrate what happens when a coil is used with a short antenna: With a 10.5 foot antenna at 3.5 mhz the capacitance of the antenna is around 30 pf. The radiation resistance is about .55 ohms This takes a 62.5 microhenry coil to equal the capactive reactance. With a Q of around 200 the coil will have a resistance of about 6.88 ohms. The coil and antenna radiation resistance will provide a load of 7.43 ohms at the feed point. (6.88 + .55 = 7.43) Additional matching will be required to get it to 50 ohms. But if you apply 100 watts to the 7.43 ohms you will have a coil / antenna current of 3.67 amps. (I squared R = 100W) Now that reactance of the coil will be 1375 ohms. So 1375 times 3.67 amps = 5046 volts rms or 7137 volts peak across the coil!! (V= IR) Who says you can’t get zapped from 100 watts! This is where your high voltage comes from with a low impedance antenna. HIGH VOLTAGE NOT IN PHASE Note that there is a phase shift across the coil so the current through the coil and the voltage across it are not in phase. That is what allows the voltage to rise so high. You can’t use ohms law here to calculate power without allowing for the phase difference. Otherwise it would look like 6900 watts was being delivered to the antenna. As you increase the length of the antenna the capacitance it represents becomes higher thus making its capacitive reactance lower. That also makes the need for inductive reactance lower and reduces the coil size and inductive reactance. By reducing inductive reactance you also reduce the voltage seen across the coil. Also increasing the length of the antenna increases its radiation resistance which requires less current through it for the same amount of power. With less current through the antenna you will have less current through the coil. So with less coil impedance and less current through it, the voltage developed across it will also be less for the same amount of power applied to the circuit. CAPACITY HATS Using a capacity hat on a short antenna increases the amount of capacitance that the antenna represents in the circuit. That decreases the capacitive reactance which increases its radiation resistance. Increasing its radiation resistance as above increases the efficiency of the system. Also less inductive reactance is needed and the associated benefits are also realized. COAX AS A FEED LINE Some have advocated using coax between the tuner and whip antenna or long wire antenna as a feeder rather than an open piece of wire. That would be ok if the antenna were not short for the frequency being used. Here is why it doesn’t work with a short antenna like a whip or long wire that is short for the frequency. With the same antenna in the example above if we used just 1.5 feet of RG 58 coax which has 21 pf /ft capacitance would give us about 30 pf capacitance. The same amount as out whip. Putting that in parallel with the antenna would drop the radiation resistance in half. This would cut the efficiency of the antenna in half! Examples above are from the 2000 ARRL handbook. After we worry about all the losses above there are the ground losses that are also in series with the antenna feed point. Those losses can be several times greater than the antenna losses. You can begin to see that a short antenna can be very inefficient. After reading this if still interested, reread my other earlier post about short SSB antennas and it may make more sense. Regards Gary |
SSB Antenna theory
So, is this something you put together? How about some references?
ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message ... This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. Also a lot of people think that the antenna has to be resonant in order to radiate well. That is also far from true. Using a coil to cancel out the reactance of the antenna forms a resonant circuit with the antenna which must be done in order to get power to the antenna. This is a different thing than the antenna being resonant itself. But the antenna itself will perform the same whether it is resonant or not. The problem is getting power to the antenna as you will see below. CURRENT DISTRIBUTION With a full quarter wave length antenna the current distribution on the antenna is more like a sine wave curve. Larger at the bottom and tapering slowly as you go up the antenna. With an antenna shorter than a quarter wave length the current is still maximum at the bottom feed point and smallest at the top. However the shape of the distribution is different. With a short base loaded antenna the current distribution is about linear. In other words it drops in direct proportion to the length of the antenna. With center loading or top hat loading the current distribution is "pushed up" the antenna. It has a higher almost constant current at the lower part of the antenna and it drops off very fast at the top. RADIATION RESISTANCE Current distribution on the antenna determines radiation resistance. Radiation resistance determines efficiency of the antenna system. The higher the radiation resistance the higher the efficiency of the system. With a more constant current distribution that center loading gives over base loading, the radiation resistance is greater on the antenna. This allows more power to be put into the antenna to radiate. Radiation resistance is not to be confused with feed point resistance. "Radiation resistance is defined as the resistance that would dissipate the same amount of power that is radiated by the antenna." As an antenna is made shorter (less than a quarter wave length) the radiation resistance drops. As radiation resistance drops you must increase the current to maintain the same amount of power to radiate. (OHMS LAW) REACTANCE Note that the larger a capacitor is the less reactance it has. The larger an inductor (coil) is the more reactance it has. A short antenna looks like a capacitor and like any capacitor it has capacitive reactance. That reactance is AC resistance. In order to get power into that antenna you must have an equal amount of inductive reactance in the circuit to cancel out the capacitive reactance. When the two are equal the circuit is said to be resonant and purely resistive. Note that when adding the inductance it changes nothing about the antenna itself. Only the reactance / impedance seen at the feed point which is the transmitter end of the coil. The shorter the antenna (less capacitance presented) the higher the capacitive reactance and thus the larger the coil required to cancel it. This means more wire in the coil. The more wire in the coil the more resistance the coil will have. (not to be confused with reactance) The more resistance it has the more loss it will have. It gets worse, because as the antenna gets shorter its radiation resistance gets smaller as the coil resistance is getting larger. The coil resistance can be 10 times or higher in resistance than the radiation resistance of the antenna. Because they are in series the same current that flows in the antenna also flows in the coil. The coil will therefore absorb most of the power. (ohms law again) By center loading the antenna rather than base loading it the current distribution is shifted in the antenna and that increases the radiation resistance of the antenna. However it is not a free lunch. The higher up you raise the coil on the antenna the more coil is required. This increases coil loss again. But the radiation resistance of the antenna goes up faster in proportion to the coil resistance so you end up with less system loss. CURRENT IN THE ANTENNA, VOLTAGE ON THE COIL When a short antenna is used some think that the current requirement is less rather than more for the antenna. This is related to the fact that the voltage at the coil-antenna junction (output terminal on your tuner) is much higher with a short antenna. Therefore the thought is "if the voltage is higher the current must be lower". Well it isn't! The reason the voltage is so high is because of the high inductive reactance of the coil in the tuner. Because the inductive reactance is high (lots of coil) the voltage goes high at that point. Here are some numbers to illustrate what happens when a coil is used with a short antenna: With a 10.5 foot antenna at 3.5 mhz the capacitance of the antenna is around 30 pf. The radiation resistance is about .55 ohms This takes a 62.5 microhenry coil to equal the capactive reactance. With a Q of around 200 the coil will have a resistance of about 6.88 ohms. The coil and antenna radiation resistance will provide a load of 7.43 ohms at the feed point. (6.88 + .55 = 7.43) Additional matching will be required to get it to 50 ohms. But if you apply 100 watts to the 7.43 ohms you will have a coil / antenna current of 3.67 amps. (I squared R = 100W) Now that reactance of the coil will be 1375 ohms. So 1375 times 3.67 amps = 5046 volts rms or 7137 volts peak across the coil!! (V= IR) Who says you can't get zapped from 100 watts! This is where your high voltage comes from with a low impedance antenna. HIGH VOLTAGE NOT IN PHASE Note that there is a phase shift across the coil so the current through the coil and the voltage across it are not in phase. That is what allows the voltage to rise so high. You can't use ohms law here to calculate power without allowing for the phase difference. Otherwise it would look like 6900 watts was being delivered to the antenna. As you increase the length of the antenna the capacitance it represents becomes higher thus making its capacitive reactance lower. That also makes the need for inductive reactance lower and reduces the coil size and inductive reactance. By reducing inductive reactance you also reduce the voltage seen across the coil. Also increasing the length of the antenna increases its radiation resistance which requires less current through it for the same amount of power. With less current through the antenna you will have less current through the coil. So with less coil impedance and less current through it, the voltage developed across it will also be less for the same amount of power applied to the circuit. CAPACITY HATS Using a capacity hat on a short antenna increases the amount of capacitance that the antenna represents in the circuit. That decreases the capacitive reactance which increases its radiation resistance. Increasing its radiation resistance as above increases the efficiency of the system. Also less inductive reactance is needed and the associated benefits are also realized. COAX AS A FEED LINE Some have advocated using coax between the tuner and whip antenna or long wire antenna as a feeder rather than an open piece of wire. That would be ok if the antenna were not short for the frequency being used. Here is why it doesn't work with a short antenna like a whip or long wire that is short for the frequency. With the same antenna in the example above if we used just 1.5 feet of RG 58 coax which has 21 pf /ft capacitance would give us about 30 pf capacitance. The same amount as out whip. Putting that in parallel with the antenna would drop the radiation resistance in half. This would cut the efficiency of the antenna in half! Examples above are from the 2000 ARRL handbook. After we worry about all the losses above there are the ground losses that are also in series with the antenna feed point. Those losses can be several times greater than the antenna losses. You can begin to see that a short antenna can be very inefficient. After reading this if still interested, reread my other earlier post about short SSB antennas and it may make more sense. Regards Gary |
SSB Antenna theory
"Doug Dotson" wrote in
: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista Don't confuse him when he's on a roll, Doug. He's been wound up like this for a week. I just hope it doesn't cause any annurisms in his brain....(c; Larry W4CSC....where the electrical length of the antenna is DIFFERENT from its physical length, so I can get the 75M vertical under a 15' interstate overpass...(c; |
SSB Antenna theory
I tried to give an abbreviated synopsis of the subject and dispel some
myths. I did not cover all the details. You need look no further than the ARRL itself for references. If you read the whole post you would see that near the bottom I credited the ARRL 2000 edition of their handbook, antenna section. The definition of "radiation resistance" is from there and the calculations of the example antenna with impedance's and voltages developed are directly from there. If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. I don't mean to discredit the ARRL but their statements in regard to tuning an antenna to a quarter wave in their older publications are misleading as evidenced by all the misconceptions that fly around. While that is a simplified explanation of what happens with the antenna matching, I suppose it was easier to propagate that (no pun intended) term for simplicity. But if you really want to understand what is going on it will get you into trouble in understanding as it is a conflict with what really happens. Regards Gary On Thu, 29 Apr 2004 20:25:53 -0400, "Doug Dotson" wrote: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. Also a lot of people think that the antenna has to be resonant in order to radiate well. That is also far from true. Using a coil to cancel out the reactance of the antenna forms a resonant circuit with the antenna which must be done in order to get power to the antenna. This is a different thing than the antenna being resonant itself. But the antenna itself will perform the same whether it is resonant or not. The problem is getting power to the antenna as you will see below. CURRENT DISTRIBUTION With a full quarter wave length antenna the current distribution on the antenna is more like a sine wave curve. Larger at the bottom and tapering slowly as you go up the antenna. With an antenna shorter than a quarter wave length the current is still maximum at the bottom feed point and smallest at the top. However the shape of the distribution is different. With a short base loaded antenna the current distribution is about linear. In other words it drops in direct proportion to the length of the antenna. With center loading or top hat loading the current distribution is "pushed up" the antenna. It has a higher almost constant current at the lower part of the antenna and it drops off very fast at the top. RADIATION RESISTANCE Current distribution on the antenna determines radiation resistance. Radiation resistance determines efficiency of the antenna system. The higher the radiation resistance the higher the efficiency of the system. With a more constant current distribution that center loading gives over base loading, the radiation resistance is greater on the antenna. This allows more power to be put into the antenna to radiate. Radiation resistance is not to be confused with feed point resistance. "Radiation resistance is defined as the resistance that would dissipate the same amount of power that is radiated by the antenna." As an antenna is made shorter (less than a quarter wave length) the radiation resistance drops. As radiation resistance drops you must increase the current to maintain the same amount of power to radiate. (OHMS LAW) REACTANCE Note that the larger a capacitor is the less reactance it has. The larger an inductor (coil) is the more reactance it has. A short antenna looks like a capacitor and like any capacitor it has capacitive reactance. That reactance is AC resistance. In order to get power into that antenna you must have an equal amount of inductive reactance in the circuit to cancel out the capacitive reactance. When the two are equal the circuit is said to be resonant and purely resistive. Note that when adding the inductance it changes nothing about the antenna itself. Only the reactance / impedance seen at the feed point which is the transmitter end of the coil. The shorter the antenna (less capacitance presented) the higher the capacitive reactance and thus the larger the coil required to cancel it. This means more wire in the coil. The more wire in the coil the more resistance the coil will have. (not to be confused with reactance) The more resistance it has the more loss it will have. It gets worse, because as the antenna gets shorter its radiation resistance gets smaller as the coil resistance is getting larger. The coil resistance can be 10 times or higher in resistance than the radiation resistance of the antenna. Because they are in series the same current that flows in the antenna also flows in the coil. The coil will therefore absorb most of the power. (ohms law again) By center loading the antenna rather than base loading it the current distribution is shifted in the antenna and that increases the radiation resistance of the antenna. However it is not a free lunch. The higher up you raise the coil on the antenna the more coil is required. This increases coil loss again. But the radiation resistance of the antenna goes up faster in proportion to the coil resistance so you end up with less system loss. CURRENT IN THE ANTENNA, VOLTAGE ON THE COIL When a short antenna is used some think that the current requirement is less rather than more for the antenna. This is related to the fact that the voltage at the coil-antenna junction (output terminal on your tuner) is much higher with a short antenna. Therefore the thought is "if the voltage is higher the current must be lower". Well it isn't! The reason the voltage is so high is because of the high inductive reactance of the coil in the tuner. Because the inductive reactance is high (lots of coil) the voltage goes high at that point. Here are some numbers to illustrate what happens when a coil is used with a short antenna: With a 10.5 foot antenna at 3.5 mhz the capacitance of the antenna is around 30 pf. The radiation resistance is about .55 ohms This takes a 62.5 microhenry coil to equal the capactive reactance. With a Q of around 200 the coil will have a resistance of about 6.88 ohms. The coil and antenna radiation resistance will provide a load of 7.43 ohms at the feed point. (6.88 + .55 = 7.43) Additional matching will be required to get it to 50 ohms. But if you apply 100 watts to the 7.43 ohms you will have a coil / antenna current of 3.67 amps. (I squared R = 100W) Now that reactance of the coil will be 1375 ohms. So 1375 times 3.67 amps = 5046 volts rms or 7137 volts peak across the coil!! (V= IR) Who says you can't get zapped from 100 watts! This is where your high voltage comes from with a low impedance antenna. HIGH VOLTAGE NOT IN PHASE Note that there is a phase shift across the coil so the current through the coil and the voltage across it are not in phase. That is what allows the voltage to rise so high. You can't use ohms law here to calculate power without allowing for the phase difference. Otherwise it would look like 6900 watts was being delivered to the antenna. As you increase the length of the antenna the capacitance it represents becomes higher thus making its capacitive reactance lower. That also makes the need for inductive reactance lower and reduces the coil size and inductive reactance. By reducing inductive reactance you also reduce the voltage seen across the coil. Also increasing the length of the antenna increases its radiation resistance which requires less current through it for the same amount of power. With less current through the antenna you will have less current through the coil. So with less coil impedance and less current through it, the voltage developed across it will also be less for the same amount of power applied to the circuit. CAPACITY HATS Using a capacity hat on a short antenna increases the amount of capacitance that the antenna represents in the circuit. That decreases the capacitive reactance which increases its radiation resistance. Increasing its radiation resistance as above increases the efficiency of the system. Also less inductive reactance is needed and the associated benefits are also realized. COAX AS A FEED LINE Some have advocated using coax between the tuner and whip antenna or long wire antenna as a feeder rather than an open piece of wire. That would be ok if the antenna were not short for the frequency being used. Here is why it doesn't work with a short antenna like a whip or long wire that is short for the frequency. With the same antenna in the example above if we used just 1.5 feet of RG 58 coax which has 21 pf /ft capacitance would give us about 30 pf capacitance. The same amount as out whip. Putting that in parallel with the antenna would drop the radiation resistance in half. This would cut the efficiency of the antenna in half! Examples above are from the 2000 ARRL handbook. After we worry about all the losses above there are the ground losses that are also in series with the antenna feed point. Those losses can be several times greater than the antenna losses. You can begin to see that a short antenna can be very inefficient. After reading this if still interested, reread my other earlier post about short SSB antennas and it may make more sense. Regards Gary |
SSB Antenna theory
First you cite several instances that the ARRL treatment is
wrong. Then you say the they finally got it right. Where are your references that substantiate either statement? Doug, k3qt s/v Callista "Gary Schafer" wrote in message ... I tried to give an abbreviated synopsis of the subject and dispel some myths. I did not cover all the details. You need look no further than the ARRL itself for references. If you read the whole post you would see that near the bottom I credited the ARRL 2000 edition of their handbook, antenna section. The definition of "radiation resistance" is from there and the calculations of the example antenna with impedance's and voltages developed are directly from there. If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. I don't mean to discredit the ARRL but their statements in regard to tuning an antenna to a quarter wave in their older publications are misleading as evidenced by all the misconceptions that fly around. While that is a simplified explanation of what happens with the antenna matching, I suppose it was easier to propagate that (no pun intended) term for simplicity. But if you really want to understand what is going on it will get you into trouble in understanding as it is a conflict with what really happens. Regards Gary On Thu, 29 Apr 2004 20:25:53 -0400, "Doug Dotson" wrote: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. Also a lot of people think that the antenna has to be resonant in order to radiate well. That is also far from true. Using a coil to cancel out the reactance of the antenna forms a resonant circuit with the antenna which must be done in order to get power to the antenna. This is a different thing than the antenna being resonant itself. But the antenna itself will perform the same whether it is resonant or not. The problem is getting power to the antenna as you will see below. CURRENT DISTRIBUTION With a full quarter wave length antenna the current distribution on the antenna is more like a sine wave curve. Larger at the bottom and tapering slowly as you go up the antenna. With an antenna shorter than a quarter wave length the current is still maximum at the bottom feed point and smallest at the top. However the shape of the distribution is different. With a short base loaded antenna the current distribution is about linear. In other words it drops in direct proportion to the length of the antenna. With center loading or top hat loading the current distribution is "pushed up" the antenna. It has a higher almost constant current at the lower part of the antenna and it drops off very fast at the top. RADIATION RESISTANCE Current distribution on the antenna determines radiation resistance. Radiation resistance determines efficiency of the antenna system. The higher the radiation resistance the higher the efficiency of the system. With a more constant current distribution that center loading gives over base loading, the radiation resistance is greater on the antenna. This allows more power to be put into the antenna to radiate. Radiation resistance is not to be confused with feed point resistance. "Radiation resistance is defined as the resistance that would dissipate the same amount of power that is radiated by the antenna." As an antenna is made shorter (less than a quarter wave length) the radiation resistance drops. As radiation resistance drops you must increase the current to maintain the same amount of power to radiate. (OHMS LAW) REACTANCE Note that the larger a capacitor is the less reactance it has. The larger an inductor (coil) is the more reactance it has. A short antenna looks like a capacitor and like any capacitor it has capacitive reactance. That reactance is AC resistance. In order to get power into that antenna you must have an equal amount of inductive reactance in the circuit to cancel out the capacitive reactance. When the two are equal the circuit is said to be resonant and purely resistive. Note that when adding the inductance it changes nothing about the antenna itself. Only the reactance / impedance seen at the feed point which is the transmitter end of the coil. The shorter the antenna (less capacitance presented) the higher the capacitive reactance and thus the larger the coil required to cancel it. This means more wire in the coil. The more wire in the coil the more resistance the coil will have. (not to be confused with reactance) The more resistance it has the more loss it will have. It gets worse, because as the antenna gets shorter its radiation resistance gets smaller as the coil resistance is getting larger. The coil resistance can be 10 times or higher in resistance than the radiation resistance of the antenna. Because they are in series the same current that flows in the antenna also flows in the coil. The coil will therefore absorb most of the power. (ohms law again) By center loading the antenna rather than base loading it the current distribution is shifted in the antenna and that increases the radiation resistance of the antenna. However it is not a free lunch. The higher up you raise the coil on the antenna the more coil is required. This increases coil loss again. But the radiation resistance of the antenna goes up faster in proportion to the coil resistance so you end up with less system loss. CURRENT IN THE ANTENNA, VOLTAGE ON THE COIL When a short antenna is used some think that the current requirement is less rather than more for the antenna. This is related to the fact that the voltage at the coil-antenna junction (output terminal on your tuner) is much higher with a short antenna. Therefore the thought is "if the voltage is higher the current must be lower". Well it isn't! The reason the voltage is so high is because of the high inductive reactance of the coil in the tuner. Because the inductive reactance is high (lots of coil) the voltage goes high at that point. Here are some numbers to illustrate what happens when a coil is used with a short antenna: With a 10.5 foot antenna at 3.5 mhz the capacitance of the antenna is around 30 pf. The radiation resistance is about .55 ohms This takes a 62.5 microhenry coil to equal the capactive reactance. With a Q of around 200 the coil will have a resistance of about 6.88 ohms. The coil and antenna radiation resistance will provide a load of 7.43 ohms at the feed point. (6.88 + .55 = 7.43) Additional matching will be required to get it to 50 ohms. But if you apply 100 watts to the 7.43 ohms you will have a coil / antenna current of 3.67 amps. (I squared R = 100W) Now that reactance of the coil will be 1375 ohms. So 1375 times 3.67 amps = 5046 volts rms or 7137 volts peak across the coil!! (V= IR) Who says you can't get zapped from 100 watts! This is where your high voltage comes from with a low impedance antenna. HIGH VOLTAGE NOT IN PHASE Note that there is a phase shift across the coil so the current through the coil and the voltage across it are not in phase. That is what allows the voltage to rise so high. You can't use ohms law here to calculate power without allowing for the phase difference. Otherwise it would look like 6900 watts was being delivered to the antenna. As you increase the length of the antenna the capacitance it represents becomes higher thus making its capacitive reactance lower. That also makes the need for inductive reactance lower and reduces the coil size and inductive reactance. By reducing inductive reactance you also reduce the voltage seen across the coil. Also increasing the length of the antenna increases its radiation resistance which requires less current through it for the same amount of power. With less current through the antenna you will have less current through the coil. So with less coil impedance and less current through it, the voltage developed across it will also be less for the same amount of power applied to the circuit. CAPACITY HATS Using a capacity hat on a short antenna increases the amount of capacitance that the antenna represents in the circuit. That decreases the capacitive reactance which increases its radiation resistance. Increasing its radiation resistance as above increases the efficiency of the system. Also less inductive reactance is needed and the associated benefits are also realized. COAX AS A FEED LINE Some have advocated using coax between the tuner and whip antenna or long wire antenna as a feeder rather than an open piece of wire. That would be ok if the antenna were not short for the frequency being used. Here is why it doesn't work with a short antenna like a whip or long wire that is short for the frequency. With the same antenna in the example above if we used just 1.5 feet of RG 58 coax which has 21 pf /ft capacitance would give us about 30 pf capacitance. The same amount as out whip. Putting that in parallel with the antenna would drop the radiation resistance in half. This would cut the efficiency of the antenna in half! Examples above are from the 2000 ARRL handbook. After we worry about all the losses above there are the ground losses that are also in series with the antenna feed point. Those losses can be several times greater than the antenna losses. You can begin to see that a short antenna can be very inefficient. After reading this if still interested, reread my other earlier post about short SSB antennas and it may make more sense. Regards Gary |
SSB Antenna theory
I take it that you are trying to learn and not just be argumentative.
If you read what I wrote, I said that in the antenna handbook that they finally have it right. Read the first three paragraphs under "TUNING TO A QUARTER WAVE" below. Regards Gary On Fri, 30 Apr 2004 00:07:54 -0400, "Doug Dotson" wrote: First you cite several instances that the ARRL treatment is wrong. Then you say the they finally got it right. Where are your references that substantiate either statement? Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I tried to give an abbreviated synopsis of the subject and dispel some myths. I did not cover all the details. You need look no further than the ARRL itself for references. If you read the whole post you would see that near the bottom I credited the ARRL 2000 edition of their handbook, antenna section. The definition of "radiation resistance" is from there and the calculations of the example antenna with impedance's and voltages developed are directly from there. If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. I don't mean to discredit the ARRL but their statements in regard to tuning an antenna to a quarter wave in their older publications are misleading as evidenced by all the misconceptions that fly around. While that is a simplified explanation of what happens with the antenna matching, I suppose it was easier to propagate that (no pun intended) term for simplicity. But if you really want to understand what is going on it will get you into trouble in understanding as it is a conflict with what really happens. Regards Gary On Thu, 29 Apr 2004 20:25:53 -0400, "Doug Dotson" wrote: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. |
SSB Antenna theory
Gary,
I'm not trying to be contrary at all. So much of what floats around on this and other forums is totally anecdotal. When it comes to electrical engineering I expect a more formal and verifiable approach. More below. Doug, k3qt s/v Callista "Gary Schafer" wrote in message ... I take it that you are trying to learn and not just be argumentative. Absolutely. I'm tired of this argument. I'd like to be up to date in the current school of thought. Kind of like that myth that you need to line your hull with yards of copper foil as a counterpoise when emperical evedence says otherwise. If you read what I wrote, I said that in the antenna handbook that they finally have it right. But the only reference you cite is the ARRL Antenna Handbook. When you say they finally got it right, you must base that on something other than the handbook itself. When you said they were wrong for so many years, you gave no reference that supports that view. When you say they finally got it right you still gave no reference to support that suposition. So what it boils down to is that the handbook used to be wrong, now is right, and you are the judge as to what was right and wrong with no independently verifiable refererence to either position. I expect this from the government, but I cannot accept if from someone that appears have a reasonable engineering background. Read the first three paragraphs under "TUNING TO A QUARTER WAVE" below. I have read it. No reference other than the ARRL itself which used to be wrong and now is right. Regards Gary On Fri, 30 Apr 2004 00:07:54 -0400, "Doug Dotson" wrote: First you cite several instances that the ARRL treatment is wrong. Then you say the they finally got it right. Where are your references that substantiate either statement? Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I tried to give an abbreviated synopsis of the subject and dispel some myths. I did not cover all the details. You need look no further than the ARRL itself for references. If you read the whole post you would see that near the bottom I credited the ARRL 2000 edition of their handbook, antenna section. The definition of "radiation resistance" is from there and the calculations of the example antenna with impedance's and voltages developed are directly from there. If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. I don't mean to discredit the ARRL but their statements in regard to tuning an antenna to a quarter wave in their older publications are misleading as evidenced by all the misconceptions that fly around. While that is a simplified explanation of what happens with the antenna matching, I suppose it was easier to propagate that (no pun intended) term for simplicity. But if you really want to understand what is going on it will get you into trouble in understanding as it is a conflict with what really happens. Regards Gary On Thu, 29 Apr 2004 20:25:53 -0400, "Doug Dotson" wrote: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. |
SSB Antenna theory
I wonder if Gary writes for World Radio magazine under the pen name of Kurt
N Sturba? Doug K7ABX "Gary Schafer" wrote in message ... I take it that you are trying to learn and not just be argumentative. If you read what I wrote, I said that in the antenna handbook that they finally have it right. Read the first three paragraphs under "TUNING TO A QUARTER WAVE" below. Regards Gary On Fri, 30 Apr 2004 00:07:54 -0400, "Doug Dotson" wrote: First you cite several instances that the ARRL treatment is wrong. Then you say the they finally got it right. Where are your references that substantiate either statement? Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I tried to give an abbreviated synopsis of the subject and dispel some myths. I did not cover all the details. You need look no further than the ARRL itself for references. If you read the whole post you would see that near the bottom I credited the ARRL 2000 edition of their handbook, antenna section. The definition of "radiation resistance" is from there and the calculations of the example antenna with impedance's and voltages developed are directly from there. If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. I don't mean to discredit the ARRL but their statements in regard to tuning an antenna to a quarter wave in their older publications are misleading as evidenced by all the misconceptions that fly around. While that is a simplified explanation of what happens with the antenna matching, I suppose it was easier to propagate that (no pun intended) term for simplicity. But if you really want to understand what is going on it will get you into trouble in understanding as it is a conflict with what really happens. Regards Gary On Thu, 29 Apr 2004 20:25:53 -0400, "Doug Dotson" wrote: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. |
SSB Antenna theory
I am not sure just what you are missing here. Or maybe I am not
understanding your question. Again I am posting the reference pages below in the antenna handbook. Not once could I find in there that they stated that a loading coil on an antenna made it into a quarter wave antenna as did earlier versions of the antenna handbook and the regular handbook. That is why I say they finally got it right. Maybe you are questioning which one is right. In the earlier handbooks the subject was more or less glossed over with poor explanation of what happens in the antenna matching. The newer antenna handbook goes into more detail. I even tell you the pages! Also if you look at my earlier post "Notes on short SSB antennas" there is a link to W8JI's web site where he discusses the same stuff that I have. He tells you why a loaded antenna is still the same length electrically as an unloaded antenna. In that post there is a copy of part of his article that deals with this topic as I credited him with. For more details look at his web site. REFERENCE 1 If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. REFERENCE 2 Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. Regards Gary On Fri, 30 Apr 2004 17:51:34 -0400, "Doug Dotson" wrote: Gary, I'm not trying to be contrary at all. So much of what floats around on this and other forums is totally anecdotal. When it comes to electrical engineering I expect a more formal and verifiable approach. More below. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I take it that you are trying to learn and not just be argumentative. Absolutely. I'm tired of this argument. I'd like to be up to date in the current school of thought. Kind of like that myth that you need to line your hull with yards of copper foil as a counterpoise when emperical evedence says otherwise. If you read what I wrote, I said that in the antenna handbook that they finally have it right. But the only reference you cite is the ARRL Antenna Handbook. When you say they finally got it right, you must base that on something other than the handbook itself. When you said they were wrong for so many years, you gave no reference that supports that view. When you say they finally got it right you still gave no reference to support that suposition. So what it boils down to is that the handbook used to be wrong, now is right, and you are the judge as to what was right and wrong with no independently verifiable refererence to either position. I expect this from the government, but I cannot accept if from someone that appears have a reasonable engineering background. Read the first three paragraphs under "TUNING TO A QUARTER WAVE" below. I have read it. No reference other than the ARRL itself which used to be wrong and now is right. Regards Gary On Fri, 30 Apr 2004 00:07:54 -0400, "Doug Dotson" wrote: First you cite several instances that the ARRL treatment is wrong. Then you say the they finally got it right. Where are your references that substantiate either statement? Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I tried to give an abbreviated synopsis of the subject and dispel some myths. I did not cover all the details. You need look no further than the ARRL itself for references. If you read the whole post you would see that near the bottom I credited the ARRL 2000 edition of their handbook, antenna section. The definition of "radiation resistance" is from there and the calculations of the example antenna with impedance's and voltages developed are directly from there. If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. I don't mean to discredit the ARRL but their statements in regard to tuning an antenna to a quarter wave in their older publications are misleading as evidenced by all the misconceptions that fly around. While that is a simplified explanation of what happens with the antenna matching, I suppose it was easier to propagate that (no pun intended) term for simplicity. But if you really want to understand what is going on it will get you into trouble in understanding as it is a conflict with what really happens. Regards Gary On Thu, 29 Apr 2004 20:25:53 -0400, "Doug Dotson" wrote: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. |
SSB Antenna theory
I guess I'll pick up the latest Antenna Handbook and start reading.
Doug, k3qt s/v Callista "Gary Schafer" wrote in message ... I am not sure just what you are missing here. Or maybe I am not understanding your question. Again I am posting the reference pages below in the antenna handbook. Not once could I find in there that they stated that a loading coil on an antenna made it into a quarter wave antenna as did earlier versions of the antenna handbook and the regular handbook. That is why I say they finally got it right. Maybe you are questioning which one is right. In the earlier handbooks the subject was more or less glossed over with poor explanation of what happens in the antenna matching. The newer antenna handbook goes into more detail. I even tell you the pages! Also if you look at my earlier post "Notes on short SSB antennas" there is a link to W8JI's web site where he discusses the same stuff that I have. He tells you why a loaded antenna is still the same length electrically as an unloaded antenna. In that post there is a copy of part of his article that deals with this topic as I credited him with. For more details look at his web site. REFERENCE 1 If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. REFERENCE 2 Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. Regards Gary On Fri, 30 Apr 2004 17:51:34 -0400, "Doug Dotson" wrote: Gary, I'm not trying to be contrary at all. So much of what floats around on this and other forums is totally anecdotal. When it comes to electrical engineering I expect a more formal and verifiable approach. More below. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I take it that you are trying to learn and not just be argumentative. Absolutely. I'm tired of this argument. I'd like to be up to date in the current school of thought. Kind of like that myth that you need to line your hull with yards of copper foil as a counterpoise when emperical evedence says otherwise. If you read what I wrote, I said that in the antenna handbook that they finally have it right. But the only reference you cite is the ARRL Antenna Handbook. When you say they finally got it right, you must base that on something other than the handbook itself. When you said they were wrong for so many years, you gave no reference that supports that view. When you say they finally got it right you still gave no reference to support that suposition. So what it boils down to is that the handbook used to be wrong, now is right, and you are the judge as to what was right and wrong with no independently verifiable refererence to either position. I expect this from the government, but I cannot accept if from someone that appears have a reasonable engineering background. Read the first three paragraphs under "TUNING TO A QUARTER WAVE" below. I have read it. No reference other than the ARRL itself which used to be wrong and now is right. Regards Gary On Fri, 30 Apr 2004 00:07:54 -0400, "Doug Dotson" wrote: First you cite several instances that the ARRL treatment is wrong. Then you say the they finally got it right. Where are your references that substantiate either statement? Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I tried to give an abbreviated synopsis of the subject and dispel some myths. I did not cover all the details. You need look no further than the ARRL itself for references. If you read the whole post you would see that near the bottom I credited the ARRL 2000 edition of their handbook, antenna section. The definition of "radiation resistance" is from there and the calculations of the example antenna with impedance's and voltages developed are directly from there. If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. I don't mean to discredit the ARRL but their statements in regard to tuning an antenna to a quarter wave in their older publications are misleading as evidenced by all the misconceptions that fly around. While that is a simplified explanation of what happens with the antenna matching, I suppose it was easier to propagate that (no pun intended) term for simplicity. But if you really want to understand what is going on it will get you into trouble in understanding as it is a conflict with what really happens. Regards Gary On Thu, 29 Apr 2004 20:25:53 -0400, "Doug Dotson" wrote: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. |
SSB Antenna theory
"Doug" wrote in
.net: I wonder if Gary writes for World Radio magazine under the pen name of Kurt N Sturba? Doug K7ABX Hee hee....(c; World Radio is the definitive answer to all broadcast engineering questions.... 73, Larry W4CSC |
SSB Antenna theory
"Doug Dotson" wrote ... I guess I'll pick up the latest Antenna Handbook and start reading. Doug, k3qt s/v Callista The fundamental work on "small" antennas was done by a guy named Wheeler. After digging in the filing cabinet I found his paper from the proceedings of the I.R.E. (institute of radio engineers?) that preceded the IEEE. "Fundamental Limitations of Small Antennas" by Harold A. Wheeler fellow, I.R.E. December 1947 One insight is that a small antenna can theoretically be nearly as efficient as a 1/4 wave element but it is difficult to match to the small radiation resistance. (actually you match to the sum of the radiation and loss resistance). The efficiency is simply the ratio of radiation resistance to the sum of radiation plus loss resistance. A small loop antenna which looks inductive makes the job easier as you can build a low resistance loop and use high Q capacitors for tuning/matching. regards, -rick- |
SSB Antenna theory
"-rick-" wrote in
: "Doug Dotson" wrote ... I guess I'll pick up the latest Antenna Handbook and start reading. Doug, k3qt s/v Callista The fundamental work on "small" antennas was done by a guy named Wheeler. After digging in the filing cabinet I found his paper from the proceedings of the I.R.E. (institute of radio engineers?) that preceded the IEEE. "Fundamental Limitations of Small Antennas" by Harold A. Wheeler fellow, I.R.E. December 1947 One insight is that a small antenna can theoretically be nearly as efficient as a 1/4 wave element but it is difficult to match to the small radiation resistance. (actually you match to the sum of the radiation and loss resistance). The efficiency is simply the ratio of radiation resistance to the sum of radiation plus loss resistance. A small loop antenna which looks inductive makes the job easier as you can build a low resistance loop and use high Q capacitors for tuning/matching. regards, -rick- In 1947, matching the very low impedance feedpoint of a loaded vertical antenna was a problem. But, after the invention of the broadband iron powder toroids that are very efficient, magnetically at high frequencies, it's not much of a problem at all. At the base of my monster 1.8-30 Mhz 15' mobile ham antenna (4' ss base, 6" diameter monster loading coil, 3' mast, 36" capacitor hat and stainless whip on top cut so that shorting the whole coil resonates it at 14.250 Mhz) is a T-200-2 powered iron toroid core wrapped with insulating fiberglass tape and 12 turns of bare #10 copper. The core is mounted in a plastic construction box between the posts of banana jacks that are soldered to the outside of each turn so banana plugs can select the turns ratio. One end of the coil is connected to "ground", the chassis of the car. Any reasonable RF grounding system would hook there on a boat. The coax from the transceiver's 650 watt, 12V linear amp is terminated with a banana plug to select the input tap, and a short length of braided strap goes between a banana plug and the bottom feed point of the antenna for the output tap. Best match occurs when the lowest reflected power occurs on the SWR meter of the linear amp (or transceiver with the linear out of the circuit). On my antenna, on the 3.5-4 Mhz ham band for instance, the input tap is across the entire 12 turns and the antenna is tapped 4 turns above the ground point. SWR at resonance is perfect, 1:1, and large corona arcs occur at the top of the whip tip and bent around ends of the 8 spokes of the 36" capacitor hat, made of stainless welding rod welded to two large flatwashers at the center. Signals are very comparible to any fixed station here running the same power. Cars passing blow horns and shout, "Your Antenna Is On Fire!", out their windows. It will light up a flourescent tube in your hand at 10' away, easily. The square of the turns ratio is 9:1 so the antenna's impedance is somewhere around 6 ohms or so at the feedpoint. The 650 W amp melted the solder joints on the core using #12 wire for the turns, so I went to #10 which is about as thick as I can go with 12 evenly spaced turns without shorts. #10 wire gets too hot to touch, but doesn't melt solder any more...(c; A second similar toroid autotransformer is mounted in another box with 24 turns of #12 next to the first. It is used for the 160 Meter band (1.8-2 Mhz). A second loading coil on top of the first (3" diam, 200T) adds sufficient inductance to tune the 15' antenna down to 1.8 Mhz, but at 650 watts there is so much corona arcing it makes the SWR readings go crazy so power is reduced to 300W or whatever the humidity around the antenna can stand at that particular moment. If one were to forego the old untuned wire/tuner marine antenna configuration and go with a real tuned vertical, this toroid autotransformer will very efficiently match the very low base impedance to the 50 ohm transceiver across the 2-30 Mhz HF band. The car's electrical wiring resonates around 3.9 Mhz, causing all the dash lights to glow brightly with SSB modulation on their own, to the amazement of even ham radio passengers. Thank God old Mercedes 220D diesels have no electronics in them! Many hams have gone to a remotely-tuned mobile antenna that uses a powered motor to move the tap on a center loading coil. Here's what it looks like: http://www.qth.com/n7lyy/about.html It uses a screwdriver DC motor to move the loading coil up and down against a large contactor and will tune the entire band. If a boater were to make the whip longer than the 66" limit for cars, it would be even more efficient with less coil turns below 12 Mhz. 66" is so it will tune 29.7 Mhz, the highest HF ham band boaters don't need. This antenna system would easily mount on a stern rail, using the rail as groundplane if it were all connected together, and would tune from the radio while watching the SWR meter on the radio (or output power meter which would just tune for maximum output power). Larry W4CSC Some day I might try this antenna using the handrails of the boat as ground plane. It's gotta work better than the stupid untuned backstay and inefficient antenna tuner. It certainly results in much better signal reports. |
SSB Antenna theory
Here's some more information on screwdriver HF antennas:
http://www.qsl.net/k4kwh/ http://www.hsantennas.com/ http://www.kj7u.com/ http://www.ko6yd.com/sam/index.htm (screwdriver antenna memory tuner) http://www.mfjenterprises.com/produc...rodid=MFJ-1662 http://texasbugcatcher.com/ (my antenna uses Henry's coils but is not a screwdriver.) http://www.mindspring.com/~k4poz/ As you can see, these antennas are very respected by the finicky ham radio mobile operators. They'll ALL tune ALL the marine bands. Larry W4CSC |
SSB Antenna theory
On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC
wrote: The square of the turns ratio is 9:1 so the antenna's impedance is somewhere around 6 ohms or so at the feedpoint. The 650 W amp melted the solder joints on the core using #12 wire for the turns, so I went to #10 If one were to forego the old untuned wire/tuner marine antenna configuration and go with a real tuned vertical, this toroid autotransformer will very efficiently match the very low base impedance to the 50 ohm transceiver across the 2-30 Mhz HF band. Larry W4CSC Some day I might try this antenna using the handrails of the boat as ground plane. It's gotta work better than the stupid untuned backstay and inefficient antenna tuner. It certainly results in much better signal reports. Your feed point resistance may be 6 ohms but about 5.8 to 5.9 ohms of that are coil resistance. The radiation resistance of the 15 foot whip on 3.5 mhz is in the order of .1 ohm. So about 97% of your power is going up in heat in the coils. Only a couple percent of the power is making it to the antenna to be radiated. Of 650 watts only around 20 watts makes it to the antenna. A full quarter wave length vertical has a radiation and feed point resistance of around 36 ohms. Much easier to get power into than a .1 ohm 15 foot antenna. Oh, don't forget to add in all the ground loss resistance too. Less power to the antenna yet. If you can get your feed point resistance down to around 1 ohm then you will get about 10% of your power into the 15 foot antenna! Regards Gary |
SSB Antenna theory
Gary Schafer wrote in
: On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC wrote: Your feed point resistance may be 6 ohms but about 5.8 to 5.9 ohms of that are coil resistance. The radiation resistance of the 15 foot whip on 3.5 mhz is in the order of .1 ohm. So about 97% of your power is going up in heat in the coils. Only a couple percent of the power is making it to the antenna to be radiated. Of 650 watts only around 20 watts makes it to the antenna. A full quarter wave length vertical has a radiation and feed point resistance of around 36 ohms. Much easier to get power into than a .1 ohm 15 foot antenna. Oh, don't forget to add in all the ground loss resistance too. Less power to the antenna yet. If you can get your feed point resistance down to around 1 ohm then you will get about 10% of your power into the 15 foot antenna! Regards Gary I've never met anyone so full of pure bull**** in my entire life as you, Gary. It's simply incredible. One hopes noone in their right mind will hire you as an engineer and suffer the consequences. I doubt 20 watts would make a signal 800 miles away at 20 over S9 in any conditions, but we're, I'm sure, gonna hear more bull**** from you about it in the near future. Larry W4CSC What class licenses and degrees do you hold, anyways? I've been a 1st phone licensee since the 1960's, an avid ham operator since 1957 when I was 10 and graduated with honors from many military electronics schools run by the US Navy because Vietnam's draft kinda got in the way of college in 1964. Stop by some time and I'll let 20 watts burn your ass for you....(c; I've never seen 20 watts produce a corona in air over 8" long.... How many kilovolts is that in air at sea level? |
SSB Antenna theory
On Tue, 04 May 2004 21:15:40 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC wrote: Your feed point resistance may be 6 ohms but about 5.8 to 5.9 ohms of that are coil resistance. The radiation resistance of the 15 foot whip on 3.5 mhz is in the order of .1 ohm. So about 97% of your power is going up in heat in the coils. Only a couple percent of the power is making it to the antenna to be radiated. Of 650 watts only around 20 watts makes it to the antenna. A full quarter wave length vertical has a radiation and feed point resistance of around 36 ohms. Much easier to get power into than a .1 ohm 15 foot antenna. Oh, don't forget to add in all the ground loss resistance too. Less power to the antenna yet. If you can get your feed point resistance down to around 1 ohm then you will get about 10% of your power into the 15 foot antenna! Regards Gary I've never met anyone so full of pure bull**** in my entire life as you, Gary. It's simply incredible. One hopes noone in their right mind will hire you as an engineer and suffer the consequences. I doubt 20 watts would make a signal 800 miles away at 20 over S9 in any conditions, but we're, I'm sure, gonna hear more bull**** from you about it in the near future. Larry W4CSC What class licenses and degrees do you hold, anyways? I've been a 1st phone licensee since the 1960's, an avid ham operator since 1957 when I was 10 and graduated with honors from many military electronics schools run by the US Navy because Vietnam's draft kinda got in the way of college in 1964. Stop by some time and I'll let 20 watts burn your ass for you....(c; I've never seen 20 watts produce a corona in air over 8" long.... How many kilovolts is that in air at sea level? Heh heh, still haven't figured it out Larry? Regards Gary |
SSB Antenna theory
On Tue, 04 May 2004 21:15:40 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC wrote: Your feed point resistance may be 6 ohms but about 5.8 to 5.9 ohms of that are coil resistance. The radiation resistance of the 15 foot whip on 3.5 mhz is in the order of .1 ohm. So about 97% of your power is going up in heat in the coils. Only a couple percent of the power is making it to the antenna to be radiated. Of 650 watts only around 20 watts makes it to the antenna. A full quarter wave length vertical has a radiation and feed point resistance of around 36 ohms. Much easier to get power into than a .1 ohm 15 foot antenna. Oh, don't forget to add in all the ground loss resistance too. Less power to the antenna yet. If you can get your feed point resistance down to around 1 ohm then you will get about 10% of your power into the 15 foot antenna! Regards Gary I've never met anyone so full of pure bull**** in my entire life as you, Gary. It's simply incredible. One hopes noone in their right mind will hire you as an engineer and suffer the consequences. I doubt 20 watts would make a signal 800 miles away at 20 over S9 in any conditions, but we're, I'm sure, gonna hear more bull**** from you about it in the near future. Larry W4CSC What class licenses and degrees do you hold, anyways? I've been a 1st phone licensee since the 1960's, an avid ham operator since 1957 when I was 10 and graduated with honors from many military electronics schools run by the US Navy because Vietnam's draft kinda got in the way of college in 1964. Stop by some time and I'll let 20 watts burn your ass for you....(c; I've never seen 20 watts produce a corona in air over 8" long.... How many kilovolts is that in air at sea level? What part do you deem to be "bull****" Larry? The parts you don't understand? I know that you like sensationalism in big arcs and bragging rights of running high power. That's fine if that's your thing but you let it cloud reality. Being able to pull a big arc from an antenna tells you nothing about its efficiency or how well it will radiate. It does make for good show though. A tesla coil will produce some pretty high voltage and corona too. By the way, time in grade doesn't count either. Being a corporal for 20 years doesn't automatically make one an expert at anything. Not that you can't be an expert, time in grade just doesn't contribute. Note that I haven't said that you are full of bull****. I am giving you the benefit of the doubt. If you went to tech school as you claim, you have forgotten some of the basics or you were asleep through many parts. I would have thought that basic AC circuit theory would have been part of your education. Maybe not. If you are interested in how this stuff really works it might help us to understand some of the things that you have misconceptions about. Here are a few questions: 1. Do you understand that when you have a capacitor and a coil in series in an AC circuit that the voltage across either can be much greater than the applied voltage to the circuit? (basic AC theory) 2. Do you understand that a coil has series resistance as well as reactance? 3. Do you understand the difference between Radiation resistance and feed point resistance? This is an important one! 4. Do you know that Radiation resistance is in series with feed point resistance. 5. Do you know that the same amount of current that flows at the feed point of the antenna is the same amount that flows in the radiation resistance of the antenna? They are in series you know. 6. I assume that you know ohms law and that if the same amount of current flows in two series resistors that the larger resistance will dissipate more power than the lower value resistor? 7. Do you understand that there is a phase shift between current and voltage across a coil in an AC circuit. 8. Do you understand that the radiation resistance gets very low in a short antenna? If you do not understand any of the above questions please let us know. That may be the reason that you are not understanding what goes on in your antenna system. What I previously wrote pertaining to the voltage developed across the coil and how low the radiation resistance can be on a short antenna was quoted directly from the 2000 ARRL handbook. If you have it look at HF mobile antennas. Page 20.46, 3rd column on the page. It explains why the voltage is 5000 volts rms across the coil with just 100 watts applied to an antenna with a radiation resistance of less than an ohm. Isn't that amazing! Must be black magic huh Larry? Or just maybe it has something to do with the above questions. Regards Gary |
SSB Antenna theory
I'm gonna jump in here -- not as an expert on antennas, but merely as someone who understands maxwell's equations and some mathematics. On 2004-05-05, Gary Schafer wrote: If you are interested in how this stuff really works it might help us to understand some of the things that you have misconceptions about. I don't think that it'll help at all to know what (if anything) he has misconceptions about. But it *would* help to have a mathematical model and a definition of terms. OK. Gary says that "your history doesn't matter; it doesn't matter what tech school you went to, etc.", and I agree to some extent. Since I didn't go to any tech school, I've got nothing to be embarassed about. I just happen to know a bit of math and physics. Here are a few questions: 2. Do you understand that a coil has series resistance as well as reactance? Wow. That's interesting. I'm just going to take a shot in the dark and assume that by "series resistance" you mean if I apply a DC voltage across the coil, and wait until the circuit reaches a steady state, I'll notice some current flowing; the ratio of the voltage applied to the steady-state current flow is what I call "series resistance." [...and you're implicitly asserting that this ratio is independent of the voltage applied, i.e., that the steady state current is linear as a function of the applied voltage"...] I expect that this assertion is true. So in other words, what you're calling "series resistance" is the real part of the (complex number) impedance, and reactance is the imaginary part. From what I've seen Larry write, I'll bet he understands that. 3. Do you understand the difference between Radiation resistance and feed point resistance? This is an important one! I'm just a farmer from the country, but where I come from, there's just impedance. I don't know how you split the real part of that complex number into two parts. Maybe where you come from, there's "carbon resistor" resistance and "thin-film" resistance, too, but I'm not sure how the electrons can tell the difference. A Google search doesn't yield any real information on "feed point resistance," so I guess that answering for myself, I can say "sure...radiation resistance is the real part of the impedance of an antenna; feed point resistance is an undefined term." There *does* seem to be widespread use of the term "feedpoint resistance," although definitions seem to be scarce as hen's teeth. Just being the ignorant sorta guy I am, I tend to gravitate towards the ones that define "feedpoint impedance;" one could then say that feedpoint resistance is the real part of that complex impedance. But that seems strikingly similar to the definition of "radiation resistance." How very odd. 4. Do you know that Radiation resistance is in series with feed point resistance. Ah...now you're losing me. For me, one of those terms is undefined, so it's hard to be "in series with" the other. And if we take "feed point" to be "feedpoint," then since the two seem to be the same, it's hard to admit that they're in series. But I'm sure you can clear this up for me. Can you just write down the equations? (with all the symbols defined -- that'll make it much clearer). 5. Do you know that the same amount of current that flows at the feed point of the antenna is the same amount that flows in the radiation resistance of the antenna? They are in series you know. "Flows in the radiation resistance?" I don't honestly know whether Larry knows more or less than you do, but at least I've never seen him write something like this. 6. I assume that you know ohms law and that if the same amount of current flows in two series resistors that the larger resistance will dissipate more power than the lower value resistor? Um...Ohm's law tells me, if I recall correctly, that for certain materials, the current flowing through them varies linearly with the applied (DC) voltage; in these cases, the ratio of the two is called the "resistance." If you think I'm being overly pedantic here, you can ask "what's the resistance of a diode?" The answer is, of course, "the current through a diode does not vary linearly as a function of the applied voltage, so it does not have a resistance." So you have to be careful about applying Ohm's law... 7. Do you understand that there is a phase shift between current and voltage across a coil in an AC circuit. I would say "an inductor has a complex impedance that happens not to be a real number, but rather one that has an imaginary part as well." 8. Do you understand that the radiation resistance gets very low in a short antenna? Uh...I guess I don't "understand" that. But if you'd write out an equation or two, I might know what you meant by it. ---------------------------------------------------------- Someone else asked a very interesting question earlier: 1. You state that some editions of some ARRL publication are wrong. 2. You state that other editions are right. You haven't told us where one finds evidence for this wrongness/correctness. Does one of them have an error in some equation? Can you construct a real circuit for which the predictions of one book are wrong and the predictions of the other are correct? Or do we just have to take your word for it that one is right, the other wrong? If it's the latter, then why bring the ARRL into it? Why don't we just agree that whatever you say is right, and whatever anyone says that appears to contradict it is wrong? It'd save a lot of writing... statement about antennas paraphrasing ARRL ahndbook deleted Isn't that amazing! Must be black magic huh Larry? Or just maybe it has something to do with the above questions. Maybe...but I'd find it more compelling if it had something to do with known (by which I mean "widely accepted and tested") physical laws like Maxwell's equations, and an analysis of the circuits in question. --John Hughes |
SSB Antenna theory
-------------------------------------------------------------------------
On Wed, 5 May 2004 09:46:52 +0000 (UTC), "John F. Hughes" wrote: I'm gonna jump in here -- not as an expert on antennas, but merely as someone who understands maxwell's equations and some mathematics. Well I don't profess to be any kind of expert either. On 2004-05-05, Gary Schafer wrote: If you are interested in how this stuff really works it might help us to understand some of the things that you have misconceptions about. I don't think that it'll help at all to know what (if anything) he has misconceptions about. But it *would* help to have a mathematical model and a definition of terms. The fact that ALL this stuff has been gone over several times and he still makes blanket statements of how it is wrong makes one wonder where the problem really is. OK. Gary says that "your history doesn't matter; it doesn't matter what tech school you went to, etc.", and I agree to some extent. Since I didn't go to any tech school, I've got nothing to be embarassed about. I just happen to know a bit of math and physics. Not really what I said. I said that "time in grade doesn't matter". Not trying to belittle anyone's education pro or con. Here are a few questions: 2. Do you understand that a coil has series resistance as well as reactance? Wow. That's interesting. I'm just going to take a shot in the dark and assume that by "series resistance" you mean if I apply a DC voltage across the coil, and wait until the circuit reaches a steady state, I'll notice some current flowing; the ratio of the voltage applied to the steady-state current flow is what I call "series resistance." [...and you're implicitly asserting that this ratio is independent of the voltage applied, i.e., that the steady state current is linear as a function of the applied voltage"...] I expect that this assertion is true. So in other words, what you're calling "series resistance" is the real part of the (complex number) impedance, and reactance is the imaginary part. From what I've seen Larry write, I'll bet he understands that. Yes, the series resistance is the "real part". However it is not just the DC resistance of the material in the coil. It is the AC resistance of the material known as skin effect, which will be greater than the DC resistance at radio frequencies. The higher the frequency the greater the skin effect. The voltage applied is irrelevant. 3. Do you understand the difference between Radiation resistance and feed point resistance? This is an important one! I'm just a farmer from the country, but where I come from, there's just impedance. I don't know how you split the real part of that complex number into two parts. Maybe where you come from, there's "carbon resistor" resistance and "thin-film" resistance, too, but I'm not sure how the electrons can tell the difference. A Google search doesn't yield any real information on "feed point resistance," so I guess that answering for myself, I can say "sure...radiation resistance is the real part of the impedance of an antenna; feed point resistance is an undefined term." There *does* seem to be widespread use of the term "feedpoint resistance," although definitions seem to be scarce as hen's teeth. Just being the ignorant sorta guy I am, I tend to gravitate towards the ones that define "feedpoint impedance;" one could then say that feedpoint resistance is the real part of that complex impedance. But that seems strikingly similar to the definition of "radiation resistance." How very odd. This is the very reason I pose the question! By making presumptions you get yourself into trouble in understanding. Don't feel alone though, because this is probably one of the most misunderstood terms with antennas. Again, I don't claim to be any sort of expert here. If you read the original post in this thread it attempts to explain it with some references too. But in a nut shell, "radiation resistance" is an imaginary term when dealing with antenna radiation. It is the amount of resistance that it would take to dissipate the same amount of power that actually is being radiated. It is pure resistance. No reactance involved. FEED POINT RESISTANCE, on the other hand is the resistance (assuming a vertical whip antenna here) seen at the base of the antenna , the feed point. It includes the radiation resistance of the antenna, the loss resistance of any coil involved and the ground resistance. They are all in series. This is with the reactance tuned out so the feed point is purely resistive. Feed point impedance would be the same thing but it may have reactance. In other words not purely resistive. 4. Do you know that Radiation resistance is in series with feed point resistance. Ah...now you're losing me. For me, one of those terms is undefined, so it's hard to be "in series with" the other. And if we take "feed point" to be "feedpoint," then since the two seem to be the same, it's hard to admit that they're in series. But I'm sure you can clear this up for me. Can you just write down the equations? (with all the symbols defined -- that'll make it much clearer). Rr + r = r feedpoint. See above. 5. Do you know that the same amount of current that flows at the feed point of the antenna is the same amount that flows in the radiation resistance of the antenna? They are in series you know. "Flows in the radiation resistance?" I don't honestly know whether Larry knows more or less than you do, but at least I've never seen him write something like this. Me either that's why I ask the question. But first you must understand what radiation resistance is. See above. 6. I assume that you know ohms law and that if the same amount of current flows in two series resistors that the larger resistance will dissipate more power than the lower value resistor? Um...Ohm's law tells me, if I recall correctly, that for certain materials, the current flowing through them varies linearly with the applied (DC) voltage; in these cases, the ratio of the two is called the "resistance." If you think I'm being overly pedantic here, you can ask "what's the resistance of a diode?" The answer is, of course, "the current through a diode does not vary linearly as a function of the applied voltage, so it does not have a resistance." So you have to be careful about applying Ohm's law... Oh the diode has resistance all right but in its case you have to define what point on the curve you are looking at. Irrelevant here though. Here we are talking about two linear resistors. Nothing complicated. 7. Do you understand that there is a phase shift between current and voltage across a coil in an AC circuit. I would say "an inductor has a complex impedance that happens not to be a real number, but rather one that has an imaginary part as well." Also true. But it also has a real phase shift. All part of understanding why there is high voltage across the loading coil. 8. Do you understand that the radiation resistance gets very low in a short antenna? Uh...I guess I don't "understand" that. But if you'd write out an equation or two, I might know what you meant by it. Rr = 395 x (h/lambda) squared Where Rr = radiation resistance h = radiator height in meters lambda = wavelength in meters (referenced from the ARRL antenna handbook) like it or not. :) ---------------------------------------------------------- Someone else asked a very interesting question earlier: 1. You state that some editions of some ARRL publication are wrong. 2. You state that other editions are right. You haven't told us where one finds evidence for this wrongness/correctness. Does one of them have an error in some equation? Can you construct a real circuit for which the predictions of one book are wrong and the predictions of the other are correct? Or do we just have to take your word for it that one is right, the other wrong? If it's the latter, then why bring the ARRL into it? Why don't we just agree that whatever you say is right, and whatever anyone says that appears to contradict it is wrong? It'd save a lot of writing... I am not going to say it again. Please READ the former posts. I have shown the references many times and explained what the errors were. And please, don't take my word for it if you have any doubts. statement about antennas paraphrasing ARRL ahndbook deleted Here I provided a reference and you don't want to consider it? But yet you ask for references. Isn't that amazing! Must be black magic huh Larry? Or just maybe it has something to do with the above questions. Maybe...but I'd find it more compelling if it had something to do with known (by which I mean "widely accepted and tested") physical laws like Maxwell's equations, and an analysis of the circuits in question. If you are really interested in learning please read the original post in this thread and go look at the web site of W8JI that I posted there. He explains this very subject very well in detail. He even throws in a little math for you. Regards Gary --John Hughes |
SSB Antenna theory
"Larry W4CSC" wrote
I've never seen 20 watts produce a corona in air over 8" long.... Awww .... my buddy's 4-watt CB does it all the time. Of course he had it peaked up at the truck stop but ... (c; 73, K3DWW |
SSB Antenna theory
"Gary Schafer" wrote in message
... On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC ...The 650 W amp melted the solder joints on the core .... So about 97% of your power is going up in heat in the coils. If Gary's right then 97% of 650 Watts otta get the coil so hot it melts solder and ... OY! That sounds dangerous to me, Larry. I think you otta send the whole rig to me so I can check it out. With a DD degree I may be the best qualified (c: |
SSB Antenna theory
On 2004-05-05, Gary Schafer wrote:
Well I don't profess to be any kind of expert either. You claimed to be expert enough to tell that Larry doesn't know what he's talking about, and to be able to distinguish the "right" material from the "wrong" as published by ARRL. That *sounds* like a claim... Yes, the series resistance is the "real part". However it is not just the DC resistance of the material in the coil. It is the AC resistance of the material known as skin effect, which will be greater than the DC resistance at radio frequencies. The higher the frequency the greater the skin effect. The voltage applied is irrelevant. Bzzt. The voltage applied is irrelevant only for linear components. But if you want to assume that antennas (and/or coils) are linear over the range of frequencies and voltages you're considering, I'm willing to go with that. Now I'll rephrase the last half of what you wrote: Every component has an impedance that may be frequency-dependent. We'll be working at a single frequency, f. The real part of the impedance of a coil at frequency f will be called the "series resistance." Series resistance = Real ( Impedance(f)) There's an equation. It DEFINES the term on the left in terms of two things on the right -- the "real part" function, which was known to Cauchy for instance, and the Impedance, which you can find in Horowitz and Hill, for instance. Write some more things like that, and I'll be running right along with you. 3. Do you understand the difference between Radiation resistance and feed point resistance? This is an important one! I'm just a farmer from the country, but where I come from, there's just impedance. I don't know how you split the real part of that complex number into two parts. Maybe where you come from, there's "carbon resistor" resistance and "thin-film" resistance, too, but I'm not sure how the electrons can tell the difference. A Google search doesn't yield any real information on "feed point resistance," so I guess that answering for myself, I can say "sure...radiation resistance is the real part of the impedance of an antenna; feed point resistance is an undefined term." There *does* seem to be widespread use of the term "feedpoint resistance," although definitions seem to be scarce as hen's teeth. Just being the ignorant sorta guy I am, I tend to gravitate towards the ones that define "feedpoint impedance;" one could then say that feedpoint resistance is the real part of that complex impedance. But that seems strikingly similar to the definition of "radiation resistance." How very odd. This is the very reason I pose the question! By making presumptions you get yourself into trouble in understanding. Don't feel alone though, because this is probably one of the most misunderstood terms with antennas. I don't think I was making any assumptions. The only term I found DEFINED was "feedpoint impedance"; I would HOPE that the definition of feedpoint resistance would be "real part of feedpoint impedance," but not all engineering is consistent in its terminology. Again, I don't claim to be any sort of expert here. If you read the original post in this thread it attempts to explain it with some references too. Uh...I read the originals. No equations, no definitions, and the websites pointed to had the same sort of blather. But in a nut shell, "radiation resistance" is an imaginary term when dealing with antenna radiation. It is the amount of resistance that it would take to dissipate the same amount of power that actually is being radiated. It is pure resistance. No reactance involved. Uh...I'm going to sound stupid here, but how do you measure "power dissipated?" And does it include, for instance, the heat generated by the wiring, etc.? Certainly that's power dissipated, but somehow it doesn't seem to capture the sense of the thing you describe above. Perhaps you could give me a definition of THAT term as well. FEED POINT RESISTANCE, on the other hand is the resistance (assuming a vertical whip antenna here) seen at the base of the antenna , the feed point. Hunh? All I know about is impedance, I'm afraid, when talking about AC signals. Can you express this thing in terms of impedance? All I want is a simple equation... It includes the radiation resistance of the antenna, the loss resistance of any coil involved and the ground resistance. They are all in series. This is with the reactance tuned out so the feed point is purely resistive. Feed point impedance would be the same thing but it may have reactance. In other words not purely resistive. Ah...so now we have a circuit. It looks something like this: AC+ -----###---%%%%------%%%%%%----AC- where the first set of "%%%" signs represent a component with the (presumed) linear behavior of the atmosphere and the second resistor (it was all I could draw) represents the (presumed) linear behaviour of the earth. And the ### is some coil at the bottom of the antenna perhaps. Maybe I've got this circuit wrong -- please correct me if this isn't the model you're using. But if it IS the model you're using, then each of the three components above has a reactance at frequency f, and you can start writing out the equations. [I should say "One could start writing out the equations"; I'm getting the sense that you cannot.] 5. Do you know that the same amount of current that flows at the feed point of the antenna is the same amount that flows in the radiation resistance of the antenna? They are in series you know. "Flows in the radiation resistance?" I don't honestly know whether Larry knows more or less than you do, but at least I've never seen him write something like this. Me either that's why I ask the question. But first you must understand what radiation resistance is. See above. Now that I "understand" that radiation resistance is a resistance that could be substituted for some part of the circuit and would dissipate the same power as the replaced part did, BUT is not actually a resistance of any part of the circuit, I cannot see how any current flows in it. 6. I assume that you know ohms law and that if the same amount of current flows in two series resistors that the larger resistance will dissipate more power than the lower value resistor? Um...Ohm's law tells me, if I recall correctly, that for certain materials, the current flowing through them varies linearly with the applied (DC) voltage; in these cases, the ratio of the two is called the "resistance." If you think I'm being overly pedantic here, you can ask "what's the resistance of a diode?" The answer is, of course, "the current through a diode does not vary linearly as a function of the applied voltage, so it does not have a resistance." So you have to be careful about applying Ohm's law... Oh the diode has resistance all right but in its case you have to define what point on the curve you are looking at. Irrelevant here though. Here we are talking about two linear resistors. Nothing complicated. No. A diode doesn't have resistance per se. It's true that the voltage/current curve is (probably) differentiable at most points, so one could speak of a "local resistance," but that doesn't mean that you can say anything relevant with Ohm's law, except if you're talking about very very tiny changes in voltage and the corresponding tiny changes in current. I *don't* believe we're talking about two linear resistors. I know I must be stupid, but if antennas were just pairs of resistors, no one could make a living designing them. I *do* suspect we're talking about some sort of collection of impedances, but I've lost any hope that you know anything about them. 7. Do you understand that there is a phase shift between current and voltage across a coil in an AC circuit. I would say "an inductor has a complex impedance that happens not to be a real number, but rather one that has an imaginary part as well." Also true. But it also has a real phase shift. Uh...are you telling me that there are two different ways to express a complex number, one of them in terms of the real and imaginary parts that sum up to give the number, and the other in terms of a magnitude and an argument? If so, deMoivre beat you to it by a few years. 8. Do you understand that the radiation resistance gets very low in a short antenna? Uh...I guess I don't "understand" that. But if you'd write out an equation or two, I might know what you meant by it. Rr = 395 x (h/lambda) squared Where Rr = radiation resistance h = radiator height in meters lambda = wavelength in meters OK. It's an equation. THIS I can work with. Presumably since you said so above, this is an equation for a vertical whip antenna. And it's certainly true that in this equation, the term Rr increases with the square of the height. I'm going to guess that one of two things is true: (a) This is your a DEFINITION of the symbol Rr, in which case your conclusion in statement 8 is true, but not interesting, or (b) You got this equation from somewhere where it is either (i) empirically observed for a wide range of values of h and lambda, and where Rr is actually defined so that it can be measured, or (ii) proved, based on some assumptions about the circuit in question (does it include a loading coil, for instance???) and a clear definition of Rr, In case b, I'd love to see the data and/or proof, but even more, I'd love to see the definition of the thing being measured (or appearing in the proof, as the case may be). (referenced from the ARRL antenna handbook) like it or not. :) Ah. Excellent. Forgive me for not having it with me; I'm in France. But if you'd type in, verbatim, their definition (NOT description) of radiation resistance, that would be great... I am not going to say it again. Please READ the former posts. I have shown the references many times and explained what the errors were. And please, don't take my word for it if you have any doubts. OK. I read 'em. The "explanations" are blather, and so I guess I'm not gonna take your word for it. If you are really interested in learning please read the original post in this thread and go look at the web site of W8JI that I posted there. He explains this very subject very well in detail. He even throws in a little math for you. I've read the original post. I think I grasped every germ of truth in it. And I've looked at W8JI's web page. The discussion in his radiation_and_fields.htm page is particularly entertaining. It's true that it ignores just a few things (like, say, Maxwell's equations, and the relativistic relationship between the electric and magnetic fields, and a few other things you can read about in, say, Purcell's lovely book on Electricty and Magnetism, semester 2 of the Berkeley Physics series; but what the hell does Purcell know? After all, he's only got a Nobel prize in physics, not a radio license...) but the gist is not uniformly awful. The part where he says that there are electric fields, magnetic fields, and electromagnetic fields is a pleasure to look at. When *I* look at Maxwell's equations, I see phi, the electric potential, and E, the electric field, and B, the magnetic field. (And if you feel giggly, you can add, say, zeta, the magnetic potential, and then declare it to be zero everywhere). No mention of a THIRD field. Live and learn, I always say. But I don't think that I want to live and learn from that particular source... By the way, he mentions a formula for radiation resistance, too (claims it's a definition, but since he's given other definitions above, this must certainly NOT be the definition. Or maybe he's just a crappy writer. Anyhow, his formula (for which he provides no proof) looks like yours. But the constant differs by a factor of five. Go figure! --John |
SSB Antenna theory
"Vito" wrote in
: "Larry W4CSC" wrote I've never seen 20 watts produce a corona in air over 8" long.... Awww .... my buddy's 4-watt CB does it all the time. Of course he had it peaked up at the truck stop but ... (c; 73, K3DWW FINALLY, someone in this thread with some common sense....(c; 73, larry W4CSC |
SSB Antenna theory
"Vito" wrote in
: "Larry W4CSC" wrote I've never seen 20 watts produce a corona in air over 8" long.... Awww .... my buddy's 4-watt CB does it all the time. Of course he had it peaked up at the truck stop but ... (c; 73, K3DWW Many of my older ham friends, who have now passed on to that great DX site in the sky, I hope, could remember the days when the engineers told the government any frequency over 2 Mhz was useless, so they gave it to the hams. The hams were too stupid to know it was useless, so went ahead anyways making DX contacts on UHF (over 2 Mhz in those days). Damned engineers have been stealing OUR frequency bands back ever since.....(c; Gary's trolling got quite a few bites, today..... Larry W4CSC |
SSB Antenna theory
"Vito" wrote in
: "Gary Schafer" wrote in message ... On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC ...The 650 W amp melted the solder joints on the core .... So about 97% of your power is going up in heat in the coils. If Gary's right then 97% of 650 Watts otta get the coil so hot it melts solder and ... OY! That sounds dangerous to me, Larry. I think you otta send the whole rig to me so I can check it out. With a DD degree I may be the best qualified (c: Many hams have made drawings of my little mobile antenna after feeling the brunt of its force in an all-out horserace between their mobiles and mine. For having only 20 watts output and being able to shed 630 watts of heat without glowing red, it does quite well for itself....(c; The coils get warm to the touch, but not as hot as our expert portends them to be..... Below 7 Mhz, where my car chassis groundplane becomes very inefficient, it's best NOT to lean against the car when the transmitter goes off. A friend of mine was leaning into the starboard window to see the dash lights glowing with RF barefoot and got quite a HOT FOOT!.....(c; Larry W4CSC QRP means any power under 1KW, right? |
SSB Antenna theory
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On Wed, 5 May 2004 22:38:54 +0000 (UTC), "John F. Hughes" wrote: On 2004-05-05, Gary Schafer wrote: Well I don't profess to be any kind of expert either. You claimed to be expert enough to tell that Larry doesn't know what he's talking about, and to be able to distinguish the "right" material from the "wrong" as published by ARRL. That *sounds* like a claim... Your definition of an expert is obviously different than mine. Yes, the series resistance is the "real part". However it is not just the DC resistance of the material in the coil. It is the AC resistance of the material known as skin effect, which will be greater than the DC resistance at radio frequencies. The higher the frequency the greater the skin effect. The voltage applied is irrelevant. Bzzt. The voltage applied is irrelevant only for linear components. But if you want to assume that antennas (and/or coils) are linear over the range of frequencies and voltages you're considering, I'm willing to go with that. Old debating tactic. Tell me I'm wrong, then agree. Now I'll rephrase the last half of what you wrote: Every component has an impedance that may be frequency-dependent. We'll be working at a single frequency, f. The real part of the impedance of a coil at frequency f will be called the "series resistance." Series resistance = Real ( Impedance(f)) There's an equation. It DEFINES the term on the left in terms of two things on the right -- the "real part" function, which was known to Cauchy for instance, and the Impedance, which you can find in Horowitz and Hill, for instance. Write some more things like that, and I'll be running right along with you. Thanks but I'll stick with my definition. 3. Do you understand the difference between Radiation resistance and feed point resistance? This is an important one! I'm just a farmer from the country, but where I come from, there's just impedance. I don't know how you split the real part of that complex number into two parts. Maybe where you come from, there's "carbon resistor" resistance and "thin-film" resistance, too, but I'm not sure how the electrons can tell the difference. A Google search doesn't yield any real information on "feed point resistance," so I guess that answering for myself, I can say "sure...radiation resistance is the real part of the impedance of an antenna; feed point resistance is an undefined term." There *does* seem to be widespread use of the term "feedpoint resistance," although definitions seem to be scarce as hen's teeth. Just being the ignorant sorta guy I am, I tend to gravitate towards the ones that define "feedpoint impedance;" one could then say that feedpoint resistance is the real part of that complex impedance. But that seems strikingly similar to the definition of "radiation resistance." How very odd. This is the very reason I pose the question! By making presumptions you get yourself into trouble in understanding. Don't feel alone though, because this is probably one of the most misunderstood terms with antennas. I don't think I was making any assumptions. The only term I found DEFINED was "feedpoint impedance"; I would HOPE that the definition of feedpoint resistance would be "real part of feedpoint impedance," but not all engineering is consistent in its terminology. Again, I don't claim to be any sort of expert here. If you read the original post in this thread it attempts to explain it with some references too. Uh...I read the originals. No equations, no definitions, and the websites pointed to had the same sort of blather. I suppose it seems so when you have little understanding on the subject and have a closed mind to such. But then I see your main interest is to try and display your debating skill. But in a nut shell, "radiation resistance" is an imaginary term when dealing with antenna radiation. It is the amount of resistance that it would take to dissipate the same amount of power that actually is being radiated. It is pure resistance. No reactance involved. Uh...I'm going to sound stupid here, but how do you measure "power dissipated?" And does it include, for instance, the heat generated by the wiring, etc.? Certainly that's power dissipated, but somehow it doesn't seem to capture the sense of the thing you describe above. Perhaps you could give me a definition of THAT term as well. Reread the above definition of radiation resistance carefully. FEED POINT RESISTANCE, on the other hand is the resistance (assuming a vertical whip antenna here) seen at the base of the antenna , the feed point. Hunh? All I know about is impedance, I'm afraid, when talking about AC signals. Can you express this thing in terms of impedance? All I want is a simple equation... Keep reading. It includes the radiation resistance of the antenna, the loss resistance of any coil involved and the ground resistance. They are all in series. This is with the reactance tuned out so the feed point is purely resistive. Feed point impedance would be the same thing but it may have reactance. In other words not purely resistive. Ah...so now we have a circuit. It looks something like this: AC+ -----###---%%%%------%%%%%%----AC- where the first set of "%%%" signs represent a component with the (presumed) linear behavior of the atmosphere and the second resistor (it was all I could draw) represents the (presumed) linear behaviour of the earth. And the ### is some coil at the bottom of the antenna perhaps. Maybe I've got this circuit wrong -- please correct me if this isn't the model you're using. But if it IS the model you're using, then each of the three components above has a reactance at frequency f, and you can start writing out the equations. [I should say "One could start writing out the equations"; I'm getting the sense that you cannot.] Yes by golly you have it! I think anyway, if I understand your writing. Yes each component has reactance as well as resistance. But when the circuit is at resonance the reactance is tuned out. It is then a pure resistive load containing only the resistive elements. Resonance is when the capacitive reactance is equal to the inductive reactance in the circuit. But then you knew that. And it doesn't matter whether I can or can't write out any formula. 5. Do you know that the same amount of current that flows at the feed point of the antenna is the same amount that flows in the radiation resistance of the antenna? They are in series you know. "Flows in the radiation resistance?" I don't honestly know whether Larry knows more or less than you do, but at least I've never seen him write something like this. Me either that's why I ask the question. But first you must understand what radiation resistance is. See above. Now that I "understand" that radiation resistance is a resistance that could be substituted for some part of the circuit and would dissipate the same power as the replaced part did, BUT is not actually a resistance of any part of the circuit, I cannot see how any current flows in it. No imagination? :) It is part of the circuit in the form of the antenna that radiates the equivalent amount of power. 6. I assume that you know ohms law and that if the same amount of current flows in two series resistors that the larger resistance will dissipate more power than the lower value resistor? Um...Ohm's law tells me, if I recall correctly, that for certain materials, the current flowing through them varies linearly with the applied (DC) voltage; in these cases, the ratio of the two is called the "resistance." If you think I'm being overly pedantic here, you can ask "what's the resistance of a diode?" The answer is, of course, "the current through a diode does not vary linearly as a function of the applied voltage, so it does not have a resistance." So you have to be careful about applying Ohm's law... Oh the diode has resistance all right but in its case you have to define what point on the curve you are looking at. Irrelevant here though. Here we are talking about two linear resistors. Nothing complicated. No. A diode doesn't have resistance per se. It's true that the voltage/current curve is (probably) differentiable at most points, so one could speak of a "local resistance," but that doesn't mean that you can say anything relevant with Ohm's law, except if you're talking about very very tiny changes in voltage and the corresponding tiny changes in current. I *don't* believe we're talking about two linear resistors. I know I must be stupid, but if antennas were just pairs of resistors, no one could make a living designing them. I *do* suspect we're talking about some sort of collection of impedances, but I've lost any hope that you know anything about them. In simple terms, any time you have a voltage applied to something that does not conduct infinite current that something is said to have resistance. It's resistance may not be stable and may change with amounts of applied voltage but it is still resistance and good old ohms law still applies for each static point. But then again this is completely irrelevant to the rest of this. Nice diversion attempt though. You seemed to have formed your opinion long ago of how things work. More debate tactics. 7. Do you understand that there is a phase shift between current and voltage across a coil in an AC circuit. I would say "an inductor has a complex impedance that happens not to be a real number, but rather one that has an imaginary part as well." Also true. But it also has a real phase shift. Uh...are you telling me that there are two different ways to express a complex number, one of them in terms of the real and imaginary parts that sum up to give the number, and the other in terms of a magnitude and an argument? If so, deMoivre beat you to it by a few years. Running low on tactics? 8. Do you understand that the radiation resistance gets very low in a short antenna? Uh...I guess I don't "understand" that. But if you'd write out an equation or two, I might know what you meant by it. Rr = 395 x (h/lambda) squared Where Rr = radiation resistance h = radiator height in meters lambda = wavelength in meters OK. It's an equation. THIS I can work with. Presumably since you said so above, this is an equation for a vertical whip antenna. And it's certainly true that in this equation, the term Rr increases with the square of the height. I'm going to guess that one of two things is true: (a) This is your a DEFINITION of the symbol Rr, in which case your conclusion in statement 8 is true, but not interesting, or (b) You got this equation from somewhere where it is either (i) empirically observed for a wide range of values of h and lambda, and where Rr is actually defined so that it can be measured, or (ii) proved, based on some assumptions about the circuit in question (does it include a loading coil, for instance???) and a clear definition of Rr, In case b, I'd love to see the data and/or proof, but even more, I'd love to see the definition of the thing being measured (or appearing in the proof, as the case may be). (referenced from the ARRL antenna handbook) like it or not. :) Ah. Excellent. Forgive me for not having it with me; I'm in France. But if you'd type in, verbatim, their definition (NOT description) of radiation resistance, that would be great... Being in France is a lame excuse. I am sure if you wanted to you could find a copy there but I am sure that you can also find it in many other books that deal with antenna theory. But then that would end the argument too easily wouldn't it. Already done several times. I am not going to say it again. Please READ the former posts. I have shown the references many times and explained what the errors were. And please, don't take my word for it if you have any doubts. OK. I read 'em. The "explanations" are blather, and so I guess I'm not gonna take your word for it. Meaning you don't understand them. If you are really interested in learning please read the original post in this thread and go look at the web site of W8JI that I posted there. He explains this very subject very well in detail. He even throws in a little math for you. I've read the original post. I think I grasped every germ of truth in it. Careful you don't get infected by it. Truth can be an awful thing to deal with. And I've looked at W8JI's web page. The discussion in his radiation_and_fields.htm page is particularly entertaining. It's true that it ignores just a few things (like, say, Maxwell's equations, and the relativistic relationship between the electric and magnetic fields, and a few other things you can read about in, say, Purcell's lovely book on Electricty and Magnetism, semester 2 of the Berkeley Physics series; but what the hell does Purcell know? After all, he's only got a Nobel prize in physics, not a radio license...) but the gist is not uniformly awful. The part where he says that there are electric fields, magnetic fields, and electromagnetic fields is a pleasure to look at. When *I* look at Maxwell's equations, I see phi, the electric potential, and E, the electric field, and B, the magnetic field. (And if you feel giggly, you can add, say, zeta, the magnetic potential, and then declare it to be zero everywhere). No mention of a THIRD field. Live and learn, I always say. But I don't think that I want to live and learn from that particular source... I see you are trying hard to sneak in some of your credentials without trying to make it obvious but you have failed. Are they imaginary or real? By the way, he mentions a formula for radiation resistance, too (claims it's a definition, but since he's given other definitions above, this must certainly NOT be the definition. Or maybe he's just a crappy writer. Anyhow, his formula (for which he provides no proof) looks like yours. But the constant differs by a factor of five. Go figure! I think that he has quoted well known antenna professors in his definition. Ones you may not be familiar with since RF and antennas are foreign to you as you have stated. Are you now the new expert? You have written many words and have said little of any substance. Only to try and twist and turn statements to make them seem unscientific. You tell me that I am wrong in my explanation and go on to say in the same paragraph you agree with me. (debate 101) Maybe you view the discussion as a contest but I don't. I am only here to try and help others understand a little about antennas. You seem more interested in winning a debate rather than providing any useful information to others. Forgive some of my seemingly snide remarks. However I think they are fitting with some of the amateur debating tactics you have presented which add nothing to the discussion of antennas. There is an entertainment value though. Regards Gary --John |
SSB Antenna theory
On 2004-05-06, Gary Schafer wrote:
Uh...I read the originals. No equations, no definitions, and the websites pointed to had the same sort of blather. I suppose it seems so when you have little understanding on the subject and have a closed mind to such. Nah. I think that it's pretty clear that the original posts had no equations. I happen to think that mathematics is the language of science, and so when words get vague and ambiguous, I ask for mathematics. That's just my idiosyncracy. In simple terms, any time you have a voltage applied to something that does not conduct infinite current that something is said to have resistance. Ah. Now I can throw away my copy of Horowitz and Hill. [description of website vs. E&M book by Purcell] I see you are trying hard to sneak in some of your credentials without trying to make it obvious but you have failed. Are they imaginary or real? Nah. I don't have any credentials here. Just an interest in science. *Purcell* has credentials. I'm just a guy who likes equations. You apparently don't. That's OK. We'll go about understanding phenomena differently. It's a big world. I have no idea whether you're right, Larry's right, or both are wrong about loaded antennas. But I do know that you're the wrong person for me to try to learn from, because you aren't willing to write definitions or equations, and those are what I use to understand science. Fortunately, there are other sources of information out there... -John |
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