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SSB antenna
I am installing an Icom 802 ssb with a 140 tuner. I am looking for
advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. |
SSB antenna
Roger wrote:
I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. The length of your boat and backstay might help us, here for the number crunchers. Test Receiver (Rx) side first, manually adjusting tuner with power off. Rx adjustments will be similar, reflecting Transmit (Tx) potential. Consider not insulating your backstay. Just disconnect it's ground / bonding at the transom. Insulate it with hose to transmit. Feed point by hanging coax centre only to the midpoint of the split, or insulate one leg of split from the centre or base and feed the other bottom. Leave coax shield unconnected at Antenna feed point. Experiment with directivity and relative sensitivity by monitoring a distant transmitter while you power in a circle, or adjust matching. You might be able to tune some by shortening the coax shield and / or connecting the shield end at the maching box or transmitter by switching R.F. capacitors in series with the shield, or disconnecting the shield from ground and connecting it to Tx ground, chassis or power lead ground. It is generally not good to use DC wiring as part of the Antenna Counterpoise, but sometimes it will work a miracle. Consequential lightning or static damage can occur, frying other stuff. Methods abound. This method of grounding can be like connecting a welder / commercial electroplater to your prop and zincs, etc. unless they are isolated, insulated from ground bonding and R.F. sources. R.F. capacitor bondings can also be cobbled to lifelines, etc, sometimes to good effect. At R.F. distances from the ground connection, ground or power return wires can become energised WRT other elements, acting as counterbalancing antenna elements. Here, the more the better, except for errant pedestrians. Antennae are like cat's wiskers, sensing the wind is easier with differential signal sensitivity, like hearing sonar returns through multi-mike differential time delay systems, steering the sense of hearing. Some bondings are to be avoided. Polarisation can also be fiddled, with goniometer tech and time delay devices. Understanding R.F. and ground / counterpoise / lightning plans is a heated subject, hereabouts. Much fun to watch. Terry K |
SSB antenna
Roger wrote:
I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. The length of your boat and backstay might help us, here for the number crunchers. Test Receiver (Rx) side first, manually adjusting tuner with power off. Rx adjustments will be similar, reflecting Transmit (Tx) potential. Consider not insulating your backstay. Just disconnect it's ground / bonding at the transom. Insulate it with hose to transmit. Feed point by hanging coax centre only to the midpoint of the split, or insulate one leg of split from the centre or base and feed the other bottom. Leave coax shield unconnected at Antenna feed point. Experiment with directivity and relative sensitivity by monitoring a distant transmitter while you power in a circle, or adjust matching. You might be able to tune some by shortening the coax shield and / or connecting the shield end at the maching box or transmitter by switching R.F. capacitors in series with the shield, or disconnecting the shield from ground and connecting it to Tx ground, chassis or power lead ground. It is generally not good to use DC wiring as part of the Antenna Counterpoise, but sometimes it will work a miracle. Consequential lightning or static damage can occur, frying other stuff. Methods abound. This method of grounding can be like connecting a welder / commercial electroplater to your prop and zincs, etc. unless they are isolated, insulated from ground bonding and R.F. sources. R.F. capacitor bondings can also be cobbled to lifelines, etc, sometimes to good effect. At R.F. distances from the ground connection, ground or power return wires can become energised WRT other elements, acting as counterbalancing antenna elements. Here, the more the better, except for errant pedestrians. Antennae are like cat's wiskers, sensing the wind is easier with differential signal sensitivity, like hearing sonar returns through multi-mike differential time delay systems, steering the sense of hearing. Some bondings are to be avoided. Polarisation can also be fiddled, with goniometer tech and time delay devices. Understanding R.F. and ground / counterpoise / lightning plans is a heated subject, hereabouts. Much fun to watch. Terry K |
SSB antenna
Roger,
We have the 23' whip and it works great. Also have a split backstay, but since the whip was on the boat when we bought it, I decided to stick with it. I'm not familiar with the 17' whip you mention. It would appear to me that you may not be abot to get good tuning acrosss the bands. The specs for the tuner say that a 23' minimum length is required if I recall correctly. Doug, k3qt s/v Callista "Roger" wrote in message om... I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. |
SSB antenna
Roger,
We have the 23' whip and it works great. Also have a split backstay, but since the whip was on the boat when we bought it, I decided to stick with it. I'm not familiar with the 17' whip you mention. It would appear to me that you may not be abot to get good tuning acrosss the bands. The specs for the tuner say that a 23' minimum length is required if I recall correctly. Doug, k3qt s/v Callista "Roger" wrote in message om... I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. |
SSB antenna
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SSB antenna
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SSB antenna
thanks for a very informative post, i've often wondered about using the
copper plate i use for a lightning ground as an rf ground. but tell me, with the long wire, do you catch any fish? ok, no hook, do the birds leave it alone? cheers bruce On Fri, 23 Apr 2004 05:06:19 +0000, Larry W4CSC wrote in part: Another great improvement when you are cruising is to keep 100' of small cable attached to the ground terminal of the tuner. Throw this cable off the stern with a small drag on its open end to make it lay out in the sea behind the boat. This makes an AMAZING RF ground! Just don't forget to coil the cable back up before entering any port and |
SSB antenna
thanks for a very informative post, i've often wondered about using the
copper plate i use for a lightning ground as an rf ground. but tell me, with the long wire, do you catch any fish? ok, no hook, do the birds leave it alone? cheers bruce On Fri, 23 Apr 2004 05:06:19 +0000, Larry W4CSC wrote in part: Another great improvement when you are cruising is to keep 100' of small cable attached to the ground terminal of the tuner. Throw this cable off the stern with a small drag on its open end to make it lay out in the sea behind the boat. This makes an AMAZING RF ground! Just don't forget to coil the cable back up before entering any port and |
SSB antenna
On Fri, 23 Apr 2004 05:06:19 -0000, Larry W4CSC
wrote: In any HF radio installation, the closer the antenna is to resonance (1/4 wavelength long or 1/2 wavelength long) at the desired operating frequency, and the further it is located in the clear from CONDUCTIVE surfaces, the better it operates. Why do you think an antenna operates better if it is resonant? Regards Gary |
SSB antenna
On Fri, 23 Apr 2004 05:06:19 -0000, Larry W4CSC
wrote: In any HF radio installation, the closer the antenna is to resonance (1/4 wavelength long or 1/2 wavelength long) at the desired operating frequency, and the further it is located in the clear from CONDUCTIVE surfaces, the better it operates. Why do you think an antenna operates better if it is resonant? Regards Gary |
SSB antenna
Another great improvement when you are cruising is to
keep 100' of small cable attached to the ground terminal of the tuner. Throw this cable off the stern with a small drag on its open end to make it lay out in the sea behind the boat. This makes an AMAZING RF ground! This must be installation dependent. I tried this and could not tell any difference between the 100' of cable trailing behind and simply connecting the ground to a thruhull. Doug, k3qt s/v Callista |
SSB antenna
Another great improvement when you are cruising is to
keep 100' of small cable attached to the ground terminal of the tuner. Throw this cable off the stern with a small drag on its open end to make it lay out in the sea behind the boat. This makes an AMAZING RF ground! This must be installation dependent. I tried this and could not tell any difference between the 100' of cable trailing behind and simply connecting the ground to a thruhull. Doug, k3qt s/v Callista |
SSB antenna
bruce wrote in
: thanks for a very informative post, i've often wondered about using the copper plate i use for a lightning ground as an rf ground. but tell me, with the long wire, do you catch any fish? ok, no hook, do the birds leave it alone? cheers bruce While fooling around with sea anchors for it, trying to get it submerged, not flying on the surface, but with some tension on it to straighten it out, I used the bottom of a beer can. (Hey, we got lots of them.) "Something" fell in love with my shiny can bottom and made off with the can bottom and about 30' of wire, where it broke. If you see a whale with a trailing wire antenna, he's my guy....(c; Larry W4CSC S/V "Lionheart" WDB6254 366920680 |
SSB antenna
bruce wrote in
: thanks for a very informative post, i've often wondered about using the copper plate i use for a lightning ground as an rf ground. but tell me, with the long wire, do you catch any fish? ok, no hook, do the birds leave it alone? cheers bruce While fooling around with sea anchors for it, trying to get it submerged, not flying on the surface, but with some tension on it to straighten it out, I used the bottom of a beer can. (Hey, we got lots of them.) "Something" fell in love with my shiny can bottom and made off with the can bottom and about 30' of wire, where it broke. If you see a whale with a trailing wire antenna, he's my guy....(c; Larry W4CSC S/V "Lionheart" WDB6254 366920680 |
SSB antenna
In order for an antenna to be a successful radiator of RF, it must radiate
TWO fields, hopefully towards the receiving station. The E-field is an electrostatic field whos origin occurs at the high voltage points on the antenna. In our short backstay case, that would be near the top insulator, which is the highest impedance point in the wire. The H-field is a magnetic field, 90 degrees physically from the E-field and expanding into space with it. One field cannot exist without the other over great distances, so the ideal situation is to have an antenna which creates both intense E and H fields radiating in a pattern towards intended receivers. on a vertical wire radiator (whip, backstay) the E field is vertical and the H field is horizontal. [whip tip or backstay insulator] | E field max here, drops to near 0 1/4 wave down the wire | then rises again to maximum 1/4 wave further down if wire | is long enough | | | | H field max at tuner if wire is shorter than 1/4 wavelength. How | much the field gets drops as wire gets to be less and less of 1/4 [tuner] wavelength. | | [ground] The ground wire and ground create an "image", an imagined antenna that looks (RF wise) like the radiator would in a mirror, creating a vertical dipole antenna with the transmitter in the middle. The shorter our radiator, the poorer its H-field end-fed with tuner like this. As many of you have observed, really short HF whip antennas just suck as radiators on the lower HF frequencies, getting worse as frequency decreases. 2 Mhz marine band antennas all sucked because in comparison to a full-sized 2 Mhz dipole, these antennas were REALLY short. This "shortness", putting a short whip on top of a heavy tuner to get it to resonate results in an intense E field from the high antenna VOLTAGE, but almost no H field as there is little antenna CURRENT at any point in the wire. The antenna current in this configuration occurs in the big loading coil inside the tuner, which is causing the high voltage at its output terminal at resonance. The current in this coil is NOT radiated as H field, so your signal stinks at the receiver as distance increases, even though your antenna system is resonant by the tuner's heavy inductance. Gary Schafer wrote in : Why do you think an antenna operates better if it is resonant? A self-resonant antenna, one that will load the transmitter without any tuner in the circuit (or bypassed if your tuner will do that), creates the maximum E and H fields at that frequency, when it is 1/4 wave, and at any length LONGER than 1/4 wave we can tune it to. Longer isn't much of an issue on a boat, unless you have room for the 107', quarter-wave tower on old 2182 marine HF emergency channel. Our antennas are always shorter, except above 12 Mhz where they become more reasonable in length. The amount of H-field it creates as a too-short wire is also VERY dependent on how much RF current we can make run to the ocean through its grounding system. Great grounding, lots of current. Poor grounding, poor current, poor H-field creation. E-fields are easy to make with tuner inductors. If you'd like to see the effect of BIG E-field creation, go to my ham radio callsign website on http://www.qrz.com/callsign/W4CSC and look at my picture. I'm holding the bottom half of a 300 KV RF feedthrough insulator, a souvenir of Reverend Stair (Overcomer Ministry's nut who broadcasts 24/7) from his pirate radio ship that was temporarily docked in Charleston before the FCC came to confiscate the 70KW HF transmitter that blew the hell out of this insulator when it flashed over right above my head! MOST impressive blast inside the fish hold of an old Canadian fishing trawler where the transmitters were mounted. E-field is that big black arc down the side of the porcelain...(c; 70KW on 41 meters is lots of fun. I love high powered transmitters. "POWER is our FRIEND." Sorry, I wandered off..... Now, we hams have other solutions than this crappy tuner at the base of your whip..... Marine radio does what it does because it's quick and dirty (not to mention yacht pretty with all its whitey fiberglass or stealth backstays). Tuners are NOT a good thing, like this. We try not to use tuners on mobile HF antennas on ham radio. Let's look at some that tune the ANTENNA to self- resonance to create big H fields..... http://www.texasbugcatcher.com/cata/tbcspec.htm Henry Allen, K5BUG, has always produced the finest "loading coils" for ham radio and other HF mobile antennas on the planet. My mobile antenna configuration has two of them, but only when I'm operating in the 1.8-2.0 Mhz ham band BELOW the 2 Mhz marine band right on top of the AM broadcast band. Above that band, I only use the #680 monstrous coil to tune an antenna I designed 25 years ago that DRAGS THE CURRENT UP THE ANTENNA. The antenna is 15' long, because the damned highway department says that's as high as a truck can be. There are two ways of getting more CURRENT up the antenna....put the antenna tuning coil about halfway up the length of it...or...put a capacitor hat near the top of it in the E-field area. The effect of doing this makes the antenna ELECTRICALLY LONGER, a lot longer, without making it physically longer. My antenna has both! King Hussein, JY1, the former King of Jordan, told my my signal was as strong as most fixed stations. I have the QSL card from His Majesty to prove it...(c; There is no tuner at the base of my antenna. The antenna is tuned to be ELECTRICALLY, 1/4 wavelength long by adjusting a shorting tap on the huge coil. Running 650 watts of RF power from a highly modified TenTec Hercules II linear amp that's not legal on marine radio, the base feedpoint impedance is about 18 ohms and produces over 6 AMPS of RF current to create huge H-fields heard on the other side of the planet! As you can see, no yachtie is going to let me put a 6" coil half way up the backstay, so we have to put up with poor signals from the damned tuners...(sigh) Geoffrey's "Lionheart", an Amel Sharki 41, does have something I want to get modified to simulate the effect of the capacitor hat of my ham antenna to make the HF wire longer. She has a triatic between the top of the main and mizzen right over the insulator of the HF insulated backstay on the main. I propose, if the masts ever get worked on, to add two insulators to the triatic, near the mast tops, to insulate it and connect a stainless cable from the antenna end of the backstay insulator to a clamp in the middle of the triatic, creating a "top hat" capacitor hat to DRAW UP that H-field current, making the antenna longer by a good bit, Electrically. Did this make more questions or answer them?? I love screwing around with antennas. I've been doing it since before I got my ham license in 1957 when I was 11. Antennas and HF propagation are fascinating subjects.... Larry W4CSC, old 1st Phone w/Radar endorsement when it meant something... S/V "Lionheart" WDB6254 366920680 |
SSB antenna
In order for an antenna to be a successful radiator of RF, it must radiate
TWO fields, hopefully towards the receiving station. The E-field is an electrostatic field whos origin occurs at the high voltage points on the antenna. In our short backstay case, that would be near the top insulator, which is the highest impedance point in the wire. The H-field is a magnetic field, 90 degrees physically from the E-field and expanding into space with it. One field cannot exist without the other over great distances, so the ideal situation is to have an antenna which creates both intense E and H fields radiating in a pattern towards intended receivers. on a vertical wire radiator (whip, backstay) the E field is vertical and the H field is horizontal. [whip tip or backstay insulator] | E field max here, drops to near 0 1/4 wave down the wire | then rises again to maximum 1/4 wave further down if wire | is long enough | | | | H field max at tuner if wire is shorter than 1/4 wavelength. How | much the field gets drops as wire gets to be less and less of 1/4 [tuner] wavelength. | | [ground] The ground wire and ground create an "image", an imagined antenna that looks (RF wise) like the radiator would in a mirror, creating a vertical dipole antenna with the transmitter in the middle. The shorter our radiator, the poorer its H-field end-fed with tuner like this. As many of you have observed, really short HF whip antennas just suck as radiators on the lower HF frequencies, getting worse as frequency decreases. 2 Mhz marine band antennas all sucked because in comparison to a full-sized 2 Mhz dipole, these antennas were REALLY short. This "shortness", putting a short whip on top of a heavy tuner to get it to resonate results in an intense E field from the high antenna VOLTAGE, but almost no H field as there is little antenna CURRENT at any point in the wire. The antenna current in this configuration occurs in the big loading coil inside the tuner, which is causing the high voltage at its output terminal at resonance. The current in this coil is NOT radiated as H field, so your signal stinks at the receiver as distance increases, even though your antenna system is resonant by the tuner's heavy inductance. Gary Schafer wrote in : Why do you think an antenna operates better if it is resonant? A self-resonant antenna, one that will load the transmitter without any tuner in the circuit (or bypassed if your tuner will do that), creates the maximum E and H fields at that frequency, when it is 1/4 wave, and at any length LONGER than 1/4 wave we can tune it to. Longer isn't much of an issue on a boat, unless you have room for the 107', quarter-wave tower on old 2182 marine HF emergency channel. Our antennas are always shorter, except above 12 Mhz where they become more reasonable in length. The amount of H-field it creates as a too-short wire is also VERY dependent on how much RF current we can make run to the ocean through its grounding system. Great grounding, lots of current. Poor grounding, poor current, poor H-field creation. E-fields are easy to make with tuner inductors. If you'd like to see the effect of BIG E-field creation, go to my ham radio callsign website on http://www.qrz.com/callsign/W4CSC and look at my picture. I'm holding the bottom half of a 300 KV RF feedthrough insulator, a souvenir of Reverend Stair (Overcomer Ministry's nut who broadcasts 24/7) from his pirate radio ship that was temporarily docked in Charleston before the FCC came to confiscate the 70KW HF transmitter that blew the hell out of this insulator when it flashed over right above my head! MOST impressive blast inside the fish hold of an old Canadian fishing trawler where the transmitters were mounted. E-field is that big black arc down the side of the porcelain...(c; 70KW on 41 meters is lots of fun. I love high powered transmitters. "POWER is our FRIEND." Sorry, I wandered off..... Now, we hams have other solutions than this crappy tuner at the base of your whip..... Marine radio does what it does because it's quick and dirty (not to mention yacht pretty with all its whitey fiberglass or stealth backstays). Tuners are NOT a good thing, like this. We try not to use tuners on mobile HF antennas on ham radio. Let's look at some that tune the ANTENNA to self- resonance to create big H fields..... http://www.texasbugcatcher.com/cata/tbcspec.htm Henry Allen, K5BUG, has always produced the finest "loading coils" for ham radio and other HF mobile antennas on the planet. My mobile antenna configuration has two of them, but only when I'm operating in the 1.8-2.0 Mhz ham band BELOW the 2 Mhz marine band right on top of the AM broadcast band. Above that band, I only use the #680 monstrous coil to tune an antenna I designed 25 years ago that DRAGS THE CURRENT UP THE ANTENNA. The antenna is 15' long, because the damned highway department says that's as high as a truck can be. There are two ways of getting more CURRENT up the antenna....put the antenna tuning coil about halfway up the length of it...or...put a capacitor hat near the top of it in the E-field area. The effect of doing this makes the antenna ELECTRICALLY LONGER, a lot longer, without making it physically longer. My antenna has both! King Hussein, JY1, the former King of Jordan, told my my signal was as strong as most fixed stations. I have the QSL card from His Majesty to prove it...(c; There is no tuner at the base of my antenna. The antenna is tuned to be ELECTRICALLY, 1/4 wavelength long by adjusting a shorting tap on the huge coil. Running 650 watts of RF power from a highly modified TenTec Hercules II linear amp that's not legal on marine radio, the base feedpoint impedance is about 18 ohms and produces over 6 AMPS of RF current to create huge H-fields heard on the other side of the planet! As you can see, no yachtie is going to let me put a 6" coil half way up the backstay, so we have to put up with poor signals from the damned tuners...(sigh) Geoffrey's "Lionheart", an Amel Sharki 41, does have something I want to get modified to simulate the effect of the capacitor hat of my ham antenna to make the HF wire longer. She has a triatic between the top of the main and mizzen right over the insulator of the HF insulated backstay on the main. I propose, if the masts ever get worked on, to add two insulators to the triatic, near the mast tops, to insulate it and connect a stainless cable from the antenna end of the backstay insulator to a clamp in the middle of the triatic, creating a "top hat" capacitor hat to DRAW UP that H-field current, making the antenna longer by a good bit, Electrically. Did this make more questions or answer them?? I love screwing around with antennas. I've been doing it since before I got my ham license in 1957 when I was 11. Antennas and HF propagation are fascinating subjects.... Larry W4CSC, old 1st Phone w/Radar endorsement when it meant something... S/V "Lionheart" WDB6254 366920680 |
SSB antenna
Larry
Thanks for the informative message. Your suggestion on feeding the backstay from both chainplates is interesting. Unfortunately I have a hydraulic backstay tensioner on one leg and a backstay radar mount on the other. Sooo I guess my alternatives a running the wire from the tuner along one leg of the split backstay (with stand-offs) to an insulated backstay going with a 23 ft whip BTY - I have already used up one chance on the MMSI code. I registered by VHF radio with Boat US prior to getting the SSB (thus now needing an FCC license). The FCC requires an new MMSI code. Larry W4CSC wrote in message ... (Roger) wrote in om: I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. In any HF radio installation, the closer the antenna is to resonance (1/4 wavelength long or 1/2 wavelength long) at the desired operating frequency, and the further it is located in the clear from CONDUCTIVE surfaces, the better it operates. 1/4 wavelength, in feet, is 234/frequency in megahertz. 234/8 Mhz = 29.25 ft. So, the 23' antenna at 8 Mhz requires less loading coil than the shorter one. quarter wavelength, or shorter, radiators require a good ground system to operate properly as that creates an "image antenna", in a boat underwater, to make a half wave dipole. Marine radio HF uses 2, 4, 6, 8, 12 and 18 Mhz, mostly the 4-8 Mhz frequency bands at night and 8 to 12 Mhz bands in the daytime is best. It's easy to get either whip to radiate on 12 or 18 Mhz. As of this particular period, you'll find few signals on 18 Mhz. Our ham 21 Mhz band has been dead, really dead, for weeks. So, the longer the whip, the better on these lower bands. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. "Lionheart" has a 50+ ft long insulated backstay length to the insulator near the mainmast. She had a very nasty problem as the boom's lifting was a stainless steel cable, grounded to the mast, which just sucked away the RF signal any time the boom was anywhere near centerlined. Replacing the steel cable with nylon eliminated this problem and still holds up the boom quite nicely. At 50 ft long, the resonant 1/4 wave freq of the backstay is around 4.6 Mhz, making her have great signals from that frequency up and a very respectible signal even in the 2 Mhz band when she has lots of loading coil inline (the tuner). This length of antenna is near 1/2 wavelength on the 8 Mhz band. A 1/2 wavelength antenna, end fed at the bottom by a good tuner, requires no ground at all to "get out" well. (The Metz VHF antenna, for instance, is an end-fed 1/2 wave on 156 Mhz Marine VHF. It requires no ground at all.) I sat at E-dock at Ashley Marina in Charleston, SC, and talked to Hawaii, Australia, Japan and New Zealand on the 14 Mhz ham band. Is the backstay grounded at the bottom end where it attaches to the fiberglass? Most aren't. So, you only need one insulator, about 2' from the top of the backstay to form the antenna. To feed the split configuration, which is fantastic for a wideband antenna, put the tuner between the two splits at the bottom, and run two, equal-length wires from the tuner's high voltage output antenna terminal to the bottom end of both port and starboard mountings. A good grounding strap to the battery negative terminal the shortest path possible, completes the installation. The longer backstay will easily outperform the short whips on the lower frequency bands. Another great improvement when you are cruising is to keep 100' of small cable attached to the ground terminal of the tuner. Throw this cable off the stern with a small drag on its open end to make it lay out in the sea behind the boat. This makes an AMAZING RF ground! Just don't forget to coil the cable back up before entering any port and backing into it under power. 100' of 1/4" or smaller stainless wire or "copperweld" antenna wire that won't corrode is great. Tie the wire to any handy handrail post or other tie point then run a slack wire to the ground terminal on the tuner. Retune every time you change from trailing wire ground to no-trailing-wire-ground condition as the impedance of the antenna system changes a lot with changes in grounding condition. It's always a good idea to push the tune button, even if the Icom is a happy camper.... Larry W4CSC S/V "Lionheart" Amel 41 ketch WDB6254 MMSI 366920680 PS - you only get TWO chances to put the MMSI into the Icom. Follow the instructions in the manual very carefully.... Call us on DSC HF...We'll do lunch!...(c; |
SSB antenna
Doug
What is the distance between the base of the antenna and the support clamp. I only have about 3 ft. Does the antenna bounce around much in rough seas. Roger "Doug Dotson" wrote in message ... Roger, We have the 23' whip and it works great. Also have a split backstay, but since the whip was on the boat when we bought it, I decided to stick with it. I'm not familiar with the 17' whip you mention. It would appear to me that you may not be abot to get good tuning acrosss the bands. The specs for the tuner say that a 23' minimum length is required if I recall correctly. Doug, k3qt s/v Callista "Roger" wrote in message om... I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. |
SSB antenna
Doug
What is the distance between the base of the antenna and the support clamp. I only have about 3 ft. Does the antenna bounce around much in rough seas. Roger "Doug Dotson" wrote in message ... Roger, We have the 23' whip and it works great. Also have a split backstay, but since the whip was on the boat when we bought it, I decided to stick with it. I'm not familiar with the 17' whip you mention. It would appear to me that you may not be abot to get good tuning acrosss the bands. The specs for the tuner say that a 23' minimum length is required if I recall correctly. Doug, k3qt s/v Callista "Roger" wrote in message om... I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. |
SSB antenna
Contrary to popular myth, an antenna does not radiate one bit better
or worse if it is resonant or not. With a short antenna the impedance gets to be really low. In the order of an ohm or so with a typical 2 mhz antenna. The problem is getting power to the low impedance antenna. Partly because of losses in matching networks and partly because of ground impedance losses. If you could get all the power into a 6" short antenna it would radiate just as well as a full quarter wave length antenna. The current is not less with a short antenna it is greater. That is the reason for the higher loss. With a very short antenna the high current in the antenna also causes losses. The current has to be greater because the impedance is lower. Nothing to do with the kind of fields that form around it. Another myth is that you can change the electrical length of an antenna by adding loading coils or other means. Electrical length of an antenna is the same as it's physical length. Plus a slight amount for propagation delay over it. The physical length of an antenna IS also it's electrical length. You can't change that. What you can change is the matching to that antenna with inductors and capacitors (or transmission line matching devices) to make the antennas impedance and reactance match your transmitter. There is no such thing as making a short antenna "look" like a quarter wave antenna by adding a coil to it. Example: If you have a physical 1/8 wave length antenna you can not make it into a quarter wave length antenna "electrically" by adding a loading coil to it. The coil may serve to help match the antenna to the transmitter but you still have an 1/8 wave length antenna electrically and physically. And again: if you can get the same amount of power into the 1/8 wave length antenna as you can get into a quarter wave length antenna, they will radiate equally as well. As far as using an antenna that is a quarter wave length long with a tuner, you are probably better off with an antenna that is something other than a quarter wave length as most tuners have a hard time dealing with resonant antennas. Regards Gary |
SSB antenna
Contrary to popular myth, an antenna does not radiate one bit better
or worse if it is resonant or not. With a short antenna the impedance gets to be really low. In the order of an ohm or so with a typical 2 mhz antenna. The problem is getting power to the low impedance antenna. Partly because of losses in matching networks and partly because of ground impedance losses. If you could get all the power into a 6" short antenna it would radiate just as well as a full quarter wave length antenna. The current is not less with a short antenna it is greater. That is the reason for the higher loss. With a very short antenna the high current in the antenna also causes losses. The current has to be greater because the impedance is lower. Nothing to do with the kind of fields that form around it. Another myth is that you can change the electrical length of an antenna by adding loading coils or other means. Electrical length of an antenna is the same as it's physical length. Plus a slight amount for propagation delay over it. The physical length of an antenna IS also it's electrical length. You can't change that. What you can change is the matching to that antenna with inductors and capacitors (or transmission line matching devices) to make the antennas impedance and reactance match your transmitter. There is no such thing as making a short antenna "look" like a quarter wave antenna by adding a coil to it. Example: If you have a physical 1/8 wave length antenna you can not make it into a quarter wave length antenna "electrically" by adding a loading coil to it. The coil may serve to help match the antenna to the transmitter but you still have an 1/8 wave length antenna electrically and physically. And again: if you can get the same amount of power into the 1/8 wave length antenna as you can get into a quarter wave length antenna, they will radiate equally as well. As far as using an antenna that is a quarter wave length long with a tuner, you are probably better off with an antenna that is something other than a quarter wave length as most tuners have a hard time dealing with resonant antennas. Regards Gary |
SSB antenna
Gary Schafer wrote in
: Contrary to popular myth, an antenna does not radiate one bit better or worse if it is resonant or not. It won't radiate much if it is not resonant. Try operating that 17' whip with no tuner. The only thing a tuner does is resonate the antenna. With a short antenna the impedance gets to be really low. In the order of an ohm or so with a typical 2 mhz antenna. The problem is getting power to the low impedance antenna. Partly because of losses in matching networks and partly because of ground impedance losses. Backwards. A 2' piece of wire on 2 Mhz has a feed point impedance damned near infinity. A resonant wire 117' long, on the other hand, has a feedpoint impedance of about 12-18 ohms if it's vertical close to ground. The reason the 2' wire won't radiate on 2 Mhz is its impedance along its entire length is so HIGH there isn't any antenna current to create an H- field to radiate. If you could get all the power into a 6" short antenna it would radiate just as well as a full quarter wave length antenna. Oh, if it were only true! All radio stations in the world could tear down those big beautiful towers that are so costly. I can get 50KW into a 6" antenna, but the voltage would be so high from the HIGH impedance we'd have trouble trying to keep it from flashing over. Been there, done that. The current is not less with a short antenna it is greater. That is the reason for the higher loss. With a very short antenna the high current in the antenna also causes losses. The current has to be greater because the impedance is lower. Nothing to do with the kind of fields that form around it. Would you like to lay your boat's title on that? A very short antenna has no current in it to speak of. Current in any radiator occurs at odd- multiples of 1/4 wavelength back from the open end (insulator). Another myth is that you can change the electrical length of an antenna by adding loading coils or other means. Electrical length of an antenna is the same as it's physical length. Plus a slight amount for propagation delay over it. Where DO you get this information? The entire purpose of adding series coils and parallel capacitor hats is to vary the ELECTRICAL length of a radiator, to make it electrically longer! The feedpoint impedance of my 15' long heavily-loaded (both with series coils and a large capacitor hat) on 3.9 Mhz is around 12 ohms....just like a 1/4 wavelength vertical radiator that is over 60 FEET long! The physical length is 15', the electrical length is 64 FEET! The physical length of an antenna IS also it's electrical length. You can't change that. What you can change is the matching to that antenna with inductors and capacitors (or transmission line matching devices) to make the antennas impedance and reactance match your transmitter. There is no such thing as making a short antenna "look" like a quarter wave antenna by adding a coil to it. Example: If you have a physical 1/8 wave length antenna you can not make it into a quarter wave length antenna "electrically" by adding a loading coil to it. The coil may serve to help match the antenna to the transmitter but you still have an 1/8 wave length antenna electrically and physically. And again: if you can get the same amount of power into the 1/8 wave length antenna as you can get into a quarter wave length antenna, they will radiate equally as well. As far as using an antenna that is a quarter wave length long with a tuner, you are probably better off with an antenna that is something other than a quarter wave length as most tuners have a hard time dealing with resonant antennas. Regards Gary Gary, which university did you learn this from? What schooling in RF engineering do you have? I'd like to take the course to expose them. Larry W4CSC "Boat electronics has nothing to do with PHYSICS and common sense." |
SSB antenna
Gary Schafer wrote in
: Contrary to popular myth, an antenna does not radiate one bit better or worse if it is resonant or not. It won't radiate much if it is not resonant. Try operating that 17' whip with no tuner. The only thing a tuner does is resonate the antenna. With a short antenna the impedance gets to be really low. In the order of an ohm or so with a typical 2 mhz antenna. The problem is getting power to the low impedance antenna. Partly because of losses in matching networks and partly because of ground impedance losses. Backwards. A 2' piece of wire on 2 Mhz has a feed point impedance damned near infinity. A resonant wire 117' long, on the other hand, has a feedpoint impedance of about 12-18 ohms if it's vertical close to ground. The reason the 2' wire won't radiate on 2 Mhz is its impedance along its entire length is so HIGH there isn't any antenna current to create an H- field to radiate. If you could get all the power into a 6" short antenna it would radiate just as well as a full quarter wave length antenna. Oh, if it were only true! All radio stations in the world could tear down those big beautiful towers that are so costly. I can get 50KW into a 6" antenna, but the voltage would be so high from the HIGH impedance we'd have trouble trying to keep it from flashing over. Been there, done that. The current is not less with a short antenna it is greater. That is the reason for the higher loss. With a very short antenna the high current in the antenna also causes losses. The current has to be greater because the impedance is lower. Nothing to do with the kind of fields that form around it. Would you like to lay your boat's title on that? A very short antenna has no current in it to speak of. Current in any radiator occurs at odd- multiples of 1/4 wavelength back from the open end (insulator). Another myth is that you can change the electrical length of an antenna by adding loading coils or other means. Electrical length of an antenna is the same as it's physical length. Plus a slight amount for propagation delay over it. Where DO you get this information? The entire purpose of adding series coils and parallel capacitor hats is to vary the ELECTRICAL length of a radiator, to make it electrically longer! The feedpoint impedance of my 15' long heavily-loaded (both with series coils and a large capacitor hat) on 3.9 Mhz is around 12 ohms....just like a 1/4 wavelength vertical radiator that is over 60 FEET long! The physical length is 15', the electrical length is 64 FEET! The physical length of an antenna IS also it's electrical length. You can't change that. What you can change is the matching to that antenna with inductors and capacitors (or transmission line matching devices) to make the antennas impedance and reactance match your transmitter. There is no such thing as making a short antenna "look" like a quarter wave antenna by adding a coil to it. Example: If you have a physical 1/8 wave length antenna you can not make it into a quarter wave length antenna "electrically" by adding a loading coil to it. The coil may serve to help match the antenna to the transmitter but you still have an 1/8 wave length antenna electrically and physically. And again: if you can get the same amount of power into the 1/8 wave length antenna as you can get into a quarter wave length antenna, they will radiate equally as well. As far as using an antenna that is a quarter wave length long with a tuner, you are probably better off with an antenna that is something other than a quarter wave length as most tuners have a hard time dealing with resonant antennas. Regards Gary Gary, which university did you learn this from? What schooling in RF engineering do you have? I'd like to take the course to expose them. Larry W4CSC "Boat electronics has nothing to do with PHYSICS and common sense." |
SSB antenna
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SSB antenna
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SSB antenna
On Sat, 24 Apr 2004 19:05:15 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : Contrary to popular myth, an antenna does not radiate one bit better or worse if it is resonant or not. It won't radiate much if it is not resonant. Try operating that 17' whip with no tuner. The only thing a tuner does is resonate the antenna. No, what the tuner does is match your feed line to your antenna. With a short antenna the impedance gets to be really low. In the order of an ohm or so with a typical 2 mhz antenna. The problem is getting power to the low impedance antenna. Partly because of losses in matching networks and partly because of ground impedance losses. Backwards. A 2' piece of wire on 2 Mhz has a feed point impedance damned near infinity. A resonant wire 117' long, on the other hand, has a feedpoint impedance of about 12-18 ohms if it's vertical close to ground. The reason the 2' wire won't radiate on 2 Mhz is its impedance along its entire length is so HIGH there isn't any antenna current to create an H- field to radiate. Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. That resistance will be a very low value. A quarter wave vertical antenna has an impedance of around 36 ohms by the way. If you could get all the power into a 6" short antenna it would radiate just as well as a full quarter wave length antenna. Oh, if it were only true! All radio stations in the world could tear down those big beautiful towers that are so costly. I can get 50KW into a 6" antenna, but the voltage would be so high from the HIGH impedance we'd have trouble trying to keep it from flashing over. Been there, done that. Please tell us how you can get 50 kw into a 6" antenna at HF? This is the problem that I am telling you. Losses are so high in the antenna and matching network that little power makes it to the antenna. But what power you do get into it will radiate just as well as the same amount of power in a larger antenna. The current is not less with a short antenna it is greater. That is the reason for the higher loss. With a very short antenna the high current in the antenna also causes losses. The current has to be greater because the impedance is lower. Nothing to do with the kind of fields that form around it. Would you like to lay your boat's title on that? A very short antenna has no current in it to speak of. Current in any radiator occurs at odd- multiples of 1/4 wavelength back from the open end (insulator). You are confusing reactive power with real power. Remember in tech school when they showed you an inductor and a capacitor in series and applied a specific amount of AC voltage. You were asked if the voltage across the inductor or capacitor could be higher than the applied voltage? Another myth is that you can change the electrical length of an antenna by adding loading coils or other means. Electrical length of an antenna is the same as it's physical length. Plus a slight amount for propagation delay over it. Where DO you get this information? The entire purpose of adding series coils and parallel capacitor hats is to vary the ELECTRICAL length of a radiator, to make it electrically longer! The feedpoint impedance of my 15' long heavily-loaded (both with series coils and a large capacitor hat) on 3.9 Mhz is around 12 ohms....just like a 1/4 wavelength vertical radiator that is over 60 FEET long! The physical length is 15', the electrical length is 64 FEET! If that were true then why wouldn't the feed point impedance of your 15 foot antenna be around 36 ohms like the full quarter wave length vertical? Sorry but your electrical length is only 15 feet. The same as the physical length. Your coil only serves as a matching device between the two sections of antenna. It is canceling out the capacitive reactance. The physical length of an antenna IS also it's electrical length. You can't change that. What you can change is the matching to that antenna with inductors and capacitors (or transmission line matching devices) to make the antennas impedance and reactance match your transmitter. There is no such thing as making a short antenna "look" like a quarter wave antenna by adding a coil to it. Example: If you have a physical 1/8 wave length antenna you can not make it into a quarter wave length antenna "electrically" by adding a loading coil to it. The coil may serve to help match the antenna to the transmitter but you still have an 1/8 wave length antenna electrically and physically. And again: if you can get the same amount of power into the 1/8 wave length antenna as you can get into a quarter wave length antenna, they will radiate equally as well. As far as using an antenna that is a quarter wave length long with a tuner, you are probably better off with an antenna that is something other than a quarter wave length as most tuners have a hard time dealing with resonant antennas. Regards Gary Gary, which university did you learn this from? What schooling in RF engineering do you have? I'd like to take the course to expose them. Read any of your mobile radio antenna handbooks. They will explain the basics in there on short antennas. Also in your regular antenna handbook read about an all band 112' dipole fed with open wire feed line. Not resonent on ANY band. Regards Gary Larry W4CSC "Boat electronics has nothing to do with PHYSICS and common sense." |
SSB antenna
On Sat, 24 Apr 2004 19:05:15 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : Contrary to popular myth, an antenna does not radiate one bit better or worse if it is resonant or not. It won't radiate much if it is not resonant. Try operating that 17' whip with no tuner. The only thing a tuner does is resonate the antenna. No, what the tuner does is match your feed line to your antenna. With a short antenna the impedance gets to be really low. In the order of an ohm or so with a typical 2 mhz antenna. The problem is getting power to the low impedance antenna. Partly because of losses in matching networks and partly because of ground impedance losses. Backwards. A 2' piece of wire on 2 Mhz has a feed point impedance damned near infinity. A resonant wire 117' long, on the other hand, has a feedpoint impedance of about 12-18 ohms if it's vertical close to ground. The reason the 2' wire won't radiate on 2 Mhz is its impedance along its entire length is so HIGH there isn't any antenna current to create an H- field to radiate. Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. That resistance will be a very low value. A quarter wave vertical antenna has an impedance of around 36 ohms by the way. If you could get all the power into a 6" short antenna it would radiate just as well as a full quarter wave length antenna. Oh, if it were only true! All radio stations in the world could tear down those big beautiful towers that are so costly. I can get 50KW into a 6" antenna, but the voltage would be so high from the HIGH impedance we'd have trouble trying to keep it from flashing over. Been there, done that. Please tell us how you can get 50 kw into a 6" antenna at HF? This is the problem that I am telling you. Losses are so high in the antenna and matching network that little power makes it to the antenna. But what power you do get into it will radiate just as well as the same amount of power in a larger antenna. The current is not less with a short antenna it is greater. That is the reason for the higher loss. With a very short antenna the high current in the antenna also causes losses. The current has to be greater because the impedance is lower. Nothing to do with the kind of fields that form around it. Would you like to lay your boat's title on that? A very short antenna has no current in it to speak of. Current in any radiator occurs at odd- multiples of 1/4 wavelength back from the open end (insulator). You are confusing reactive power with real power. Remember in tech school when they showed you an inductor and a capacitor in series and applied a specific amount of AC voltage. You were asked if the voltage across the inductor or capacitor could be higher than the applied voltage? Another myth is that you can change the electrical length of an antenna by adding loading coils or other means. Electrical length of an antenna is the same as it's physical length. Plus a slight amount for propagation delay over it. Where DO you get this information? The entire purpose of adding series coils and parallel capacitor hats is to vary the ELECTRICAL length of a radiator, to make it electrically longer! The feedpoint impedance of my 15' long heavily-loaded (both with series coils and a large capacitor hat) on 3.9 Mhz is around 12 ohms....just like a 1/4 wavelength vertical radiator that is over 60 FEET long! The physical length is 15', the electrical length is 64 FEET! If that were true then why wouldn't the feed point impedance of your 15 foot antenna be around 36 ohms like the full quarter wave length vertical? Sorry but your electrical length is only 15 feet. The same as the physical length. Your coil only serves as a matching device between the two sections of antenna. It is canceling out the capacitive reactance. The physical length of an antenna IS also it's electrical length. You can't change that. What you can change is the matching to that antenna with inductors and capacitors (or transmission line matching devices) to make the antennas impedance and reactance match your transmitter. There is no such thing as making a short antenna "look" like a quarter wave antenna by adding a coil to it. Example: If you have a physical 1/8 wave length antenna you can not make it into a quarter wave length antenna "electrically" by adding a loading coil to it. The coil may serve to help match the antenna to the transmitter but you still have an 1/8 wave length antenna electrically and physically. And again: if you can get the same amount of power into the 1/8 wave length antenna as you can get into a quarter wave length antenna, they will radiate equally as well. As far as using an antenna that is a quarter wave length long with a tuner, you are probably better off with an antenna that is something other than a quarter wave length as most tuners have a hard time dealing with resonant antennas. Regards Gary Gary, which university did you learn this from? What schooling in RF engineering do you have? I'd like to take the course to expose them. Read any of your mobile radio antenna handbooks. They will explain the basics in there on short antennas. Also in your regular antenna handbook read about an all band 112' dipole fed with open wire feed line. Not resonent on ANY band. Regards Gary Larry W4CSC "Boat electronics has nothing to do with PHYSICS and common sense." |
SSB antenna
Roger,
They way mine is installed is the base is secured to the transom with a standard mounting, but there is a clamp on the side of the radar arch that secures the lower portion about 6 feet above the base. No problems with excessive movement in a seaway. If you don't have an arch, them perhaps a couple of braces bay do the trick. Doug s/v Callista "Roger" wrote in message m... Doug What is the distance between the base of the antenna and the support clamp. I only have about 3 ft. Does the antenna bounce around much in rough seas. Roger "Doug Dotson" wrote in message ... Roger, We have the 23' whip and it works great. Also have a split backstay, but since the whip was on the boat when we bought it, I decided to stick with it. I'm not familiar with the 17' whip you mention. It would appear to me that you may not be abot to get good tuning acrosss the bands. The specs for the tuner say that a 23' minimum length is required if I recall correctly. Doug, k3qt s/v Callista "Roger" wrote in message om... I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. |
SSB antenna
Roger,
They way mine is installed is the base is secured to the transom with a standard mounting, but there is a clamp on the side of the radar arch that secures the lower portion about 6 feet above the base. No problems with excessive movement in a seaway. If you don't have an arch, them perhaps a couple of braces bay do the trick. Doug s/v Callista "Roger" wrote in message m... Doug What is the distance between the base of the antenna and the support clamp. I only have about 3 ft. Does the antenna bounce around much in rough seas. Roger "Doug Dotson" wrote in message ... Roger, We have the 23' whip and it works great. Also have a split backstay, but since the whip was on the boat when we bought it, I decided to stick with it. I'm not familiar with the 17' whip you mention. It would appear to me that you may not be abot to get good tuning acrosss the bands. The specs for the tuner say that a 23' minimum length is required if I recall correctly. Doug, k3qt s/v Callista "Roger" wrote in message om... I am installing an Icom 802 ssb with a 140 tuner. I am looking for advice/experience on the difference in performance between Shakespeare's 17'6" whip vs. the 23' whip. I have a sloop with a split backstay and probably will go with a whip.I only have about 3' between the antenna base and the mounting clamp on the transom. Insulating the backstay and running the feed wire along the split (through the bimini) is my second choice. |
SSB antenna
Gary Schafer wrote in
: Ok, uncle, you win...... Everything everyone teaches is wrong, including me.... |
SSB antenna
Gary Schafer wrote in
: Ok, uncle, you win...... Everything everyone teaches is wrong, including me.... |
SSB antenna
On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer
wrote: Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. ============================================= I follow what you are saying but isn't that also the definition of resonance, i.e., the point where capacitive reactance cancels inductive reactance? |
SSB antenna
On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer
wrote: Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. ============================================= I follow what you are saying but isn't that also the definition of resonance, i.e., the point where capacitive reactance cancels inductive reactance? |
SSB antenna
On Sun, 25 Apr 2004 08:56:23 -0400, Wayne.B
wrote: On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer wrote: Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. ============================================= I follow what you are saying but isn't that also the definition of resonance, i.e., the point where capacitive reactance cancels inductive reactance? When you cancel the capacitive reactance seen at the bottom of the antenna with an equal amount of inductive reactance you see a pure resistance at the other end of the coil (transmitter end). But that does not change anything in the antenna itself. The shorter an antenna is (from a quarter wave length) the lower it's radiation resistance is. If you want to put the same amount of power into it as you did when it was longer then you must put more current into it. Just simple ohms law at this point. As long as you are dealing with pure resistance, which you are when you cancel the reactance. However, you can not use simple ohms law when dealing with a reactance, which is what Larry is trying to do. Yes there will be very high voltages at the output of the antenna tuner with a short antenna connected to it. But it is because of the reactance of the coil. That voltage is not in phase with the current at that point. Take the example that I posed to Larry about the capacitor and inductor in series connected to an AC supply. There will be a specific amount of current flowing in the circuit. You will measure a voltage across the inductor. That voltage can be much higher than the voltage from the AC supply. If you multiply that voltage by the circuit current it will appear as though you have more power in the circuit than what the AC supply is actually putting out! That looks like free energy! You have to take into account the phase shift (also called power factor) that happens across the inductor. The same thing happens with the antenna tuner situation. You can not say "because the voltage is high the current must therefore be low", like Larry wants to do. The voltage is high and so is the current. BUT THEY ARE NOT IN PHASE. There are extremely high currents in the system. The high current in the coil is what causes I squared R loss (power lose). In the information in my other post about short antennas, the coil has a resistance of around 10 ohms and the radiation resistance of the short antenna was only .3 ohms. So you can see that the coil will suck up most of the power. That is why a short antenna is less efficient than a longer one. Not because a short antenna radiates poorer than a longer one. An antenna will radiate just as well if it is resonant or not. Provided you get the same amount of power to it. The E field and H field of an antenna aren't necessarily the same. They do balance themselves out as they propagate in free space. Has nothing to do with how well it radiates. Regards Gary |
SSB antenna
On Sun, 25 Apr 2004 08:56:23 -0400, Wayne.B
wrote: On Sat, 24 Apr 2004 21:45:17 GMT, Gary Schafer wrote: Your 2' piece of wire has a high capacitive REACTANCE. In order to get power into it you need an equal inductive reactance (coil) to cancel the capactive reactance to make it appear resistive. ============================================= I follow what you are saying but isn't that also the definition of resonance, i.e., the point where capacitive reactance cancels inductive reactance? When you cancel the capacitive reactance seen at the bottom of the antenna with an equal amount of inductive reactance you see a pure resistance at the other end of the coil (transmitter end). But that does not change anything in the antenna itself. The shorter an antenna is (from a quarter wave length) the lower it's radiation resistance is. If you want to put the same amount of power into it as you did when it was longer then you must put more current into it. Just simple ohms law at this point. As long as you are dealing with pure resistance, which you are when you cancel the reactance. However, you can not use simple ohms law when dealing with a reactance, which is what Larry is trying to do. Yes there will be very high voltages at the output of the antenna tuner with a short antenna connected to it. But it is because of the reactance of the coil. That voltage is not in phase with the current at that point. Take the example that I posed to Larry about the capacitor and inductor in series connected to an AC supply. There will be a specific amount of current flowing in the circuit. You will measure a voltage across the inductor. That voltage can be much higher than the voltage from the AC supply. If you multiply that voltage by the circuit current it will appear as though you have more power in the circuit than what the AC supply is actually putting out! That looks like free energy! You have to take into account the phase shift (also called power factor) that happens across the inductor. The same thing happens with the antenna tuner situation. You can not say "because the voltage is high the current must therefore be low", like Larry wants to do. The voltage is high and so is the current. BUT THEY ARE NOT IN PHASE. There are extremely high currents in the system. The high current in the coil is what causes I squared R loss (power lose). In the information in my other post about short antennas, the coil has a resistance of around 10 ohms and the radiation resistance of the short antenna was only .3 ohms. So you can see that the coil will suck up most of the power. That is why a short antenna is less efficient than a longer one. Not because a short antenna radiates poorer than a longer one. An antenna will radiate just as well if it is resonant or not. Provided you get the same amount of power to it. The E field and H field of an antenna aren't necessarily the same. They do balance themselves out as they propagate in free space. Has nothing to do with how well it radiates. Regards Gary |
SSB antenna
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SSB antenna
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