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SSB Antenna connection
"Meindert Sprang" wrote
"Jack Painter" wrote in message news:p3lvc.5786$Y21.4832@lakeread02... C'mon ol' salt, you should know the inside of copper pipe is electrically identical to both sides of copper strap when a bonding connection is made to either. Skin effect of electrical current is felt equally on both in _that_ condition. No it isn't. Consider a massive rod of 1". RF flows at the outside due to skin effect. No remove the innards of the rod, leaving, say 1/16" of wall. Why would current suddenly flow at the inner surface? It isn't, for the same reason it was on the outside when the rod was massive. Besides, heavy coils in radio stations are all tubes and cooled by running water through them. Due to the skinn effect, the water is not 'touched' by the RF. Electromagnetic induction on a material from one outside direction sees skin effect on the outside surface only of a closed structure, cabinet, pipe, etc. But we are not talking about EMF's. Yes we are. And EMF is exactly the reason why the electrons start to repell eachother. And the only place where they are as far apart as possible is on the outside of the tube. Meindert, water is not a good conductor, with average tap water having 100,000 ohms resistance across 1 meter of 15mm plastic pipe filled with water. Even at RF frequencies, where skin effect is most pronounced, a bonded connection made equally to both inside and outside of a copper pipe should exhibit skin effect throughout most of the entire cross section of the copper pipe. This is because the wall thickness of the copper pipe is not materially different from copper strap. Example: For copper tubing used as a inductor in antenna tuners: coil length R= --------------------------------------- conductivity *skindepth*2pi*coil radius Now, applying voltage to the outer surface only of copper tubing with closed ends, whether by EMF attachment or bonded connection to the outside only, would exhibit surface-only skin effect similar to if a faraday cage was constructed of the same copper strap we are talking about. The outside surface would carry most current. But if the voltage connection was bonded to both inside and outside of an opening of the faraday box or the copper tubing, then current via skin effect would be nearly constant on the inside and outside surfaces of the box, defeating the faraday effect. The condition I originally described, that of a bonded connection, applies voltage equally and carries current equally on the entire skin of the conductor, inside and out, 360 degrees, as efficiently as a piece of copper strap of similar cross section. Best regards, Jack Painter Virginia Beach, Va |
SSB Antenna connection
In article Wmnvc.6104$Y21.5577@lakeread02,
"Jack Painter" wrote: Meindert, water is not a good conductor, with average tap water having 100,000 ohms resistance across 1 meter of 15mm plastic pipe filled with water. Even at RF frequencies, where skin effect is most pronounced, a bonded connection made equally to both inside and outside of a copper pipe should exhibit skin effect throughout most of the entire cross section of the copper pipe. This is because the wall thickness of the copper pipe is not materially different from copper strap. Example: For copper tubing used as a inductor in antenna tuners: coil length R= --------------------------------------- conductivity *skindepth*2pi*coil radius Now, applying voltage to the outer surface only of copper tubing with closed ends, whether by EMF attachment or bonded connection to the outside only, would exhibit surface-only skin effect similar to if a faraday cage was constructed of the same copper strap we are talking about. The outside surface would carry most current. But if the voltage connection was bonded to both inside and outside of an opening of the faraday box or the copper tubing, then current via skin effect would be nearly constant on the inside and outside surfaces of the box, defeating the faraday effect. The condition I originally described, that of a bonded connection, applies voltage equally and carries current equally on the entire skin of the conductor, inside and out, 360 degrees, as efficiently as a piece of copper strap of similar cross section. Best regards, Jack Painter Virginia Beach, Va Jeeezzz Louise Jack, where did you learn all this BS that your spreading. But if the voltage connection was bonded to both inside and outside of an opening of the faraday box or the copper tubing, then current via skin effect would be nearly constant on the inside and outside surfaces of the box, defeating the faraday effect. Please explain how one "BONDS" a connection to only the inside of a copper pipe. All of the Physic Professors of the World would really like to know. Are you saying that if one made a "RF Connection", to only the inside of a copper tube, that no RF would flow on the outside of the tube? That is just plain wrong, and a stupid statement on it's face. ok, enough of this BS, CFR!!! (Call for Reference) Let's see if old Jack can actually come up with some documentation that RF flows on the inside of a connected copper tube or pipe. Lets go for some Peer Reviewed Documentation here, the straight, No ****, Textbook, kind of documentation, written by some really Qualified Physics Phd's. Hmmmm, all the PhdEE's that I asked, just laughed and ask how the weather and fishing was......... Bruce in alaska -- add a 2 before @ |
SSB Antenna connection
"Bruce in Alaska" wrote
"Jack Painter" wrote: Meindert, water is not a good conductor, with average tap water having 100,000 ohms resistance across 1 meter of 15mm plastic pipe filled with water. Even at RF frequencies, where skin effect is most pronounced, a bonded connection made equally to both inside and outside of a copper pipe should exhibit skin effect throughout most of the entire cross section of the copper pipe. This is because the wall thickness of the copper pipe is not materially different from copper strap. Example: For copper tubing used as a inductor in antenna tuners: coil length R= --------------------------------------- conductivity *skindepth*2pi*coil radius Now, applying voltage to the outer surface only of copper tubing with closed ends, whether by EMF attachment or bonded connection to the outside only, would exhibit surface-only skin effect similar to if a faraday cage was constructed of the same copper strap we are talking about. The outside surface would carry most current. But if the voltage connection was bonded to both inside and outside of an opening of the faraday box or the copper tubing, then current via skin effect would be nearly constant on the inside and outside surfaces of the box, defeating the faraday effect. The condition I originally described, that of a bonded connection, applies voltage equally and carries current equally on the entire skin of the conductor, inside and out, 360 degrees, as efficiently as a piece of copper strap of similar cross section. Best regards, Jack Painter Virginia Beach, Va Jeeezzz Louise Jack, where did you learn all this BS that your spreading. But if the voltage connection was bonded to both inside and outside of an opening of the faraday box or the copper tubing, then current via skin effect would be nearly constant on the inside and outside surfaces of the box, defeating the faraday effect. Please explain how one "BONDS" a connection to only the inside of a copper pipe. All of the Physic Professors of the World would really like to know. Are you saying that if one made a "RF Connection", to only the inside of a copper tube, that no RF would flow on the outside of the tube? That is just plain wrong, and a stupid statement on it's face. ok, enough of this BS, CFR!!! (Call for Reference) Let's see if old Jack can actually come up with some documentation that RF flows on the inside of a connected copper tube or pipe. Lets go for some Peer Reviewed Documentation here, the straight, No ****, Textbook, kind of documentation, written by some really Qualified Physics Phd's. Hmmmm, all the PhdEE's that I asked, just laughed and ask how the weather and fishing was......... Bruce, you're making a totally off the wall argument now, with opposite assumptions that were never asserted or offered by any of the posters to this thread. Taking your questions literally as you phrased them would generate a laugh by all, indeed. If a laugh was your intention, we'll all have a good one. But I doubt that you are confused about skin effect, or why a faraday cage works, and specifically what would defeat it's protection (ie: an opening). So if you seriously think that for instance, a c-clamp applied across an open end of thin walled copper tubing, contacting the inner and outer wall in it's grip, would apply voltage differently to the inside versus the outside of this tubing, then it will be easy to explain your error in thinking. And since I did not make a joke of your obvious geometry and math errors in determining the surface area of an object, one which you continue to be confused about, I would suggest that we either: end the thread if you do not desire pleasant and professional discussion, or, omitting the snide comments that do not reflect well on the group or it's interested participants. Respectfully, Jack Painter Virginia Beach, Va |
SSB Antenna connection
"Meindert Sprang" wrote in
: Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of about 200 ohms at 4 MHz) does to a high impedance (several kOhms at 4MHz) antenna connection: right... almost short circuit it to ground. NEVER use coax between the ATU and the antenna. That's just about as bad as neatly tywrapping the wire from the tuner to the bottom insulator on the backstay to the grounded backstay part UNDER the bottom insulator. Trying to get them to let that wire HANG away from everything to lower the capacitance to ground is like trying to get 5200 adhesive that's hardened out of a crack in the decking. They don't care what it does to the signal output, as long as it looks "neat and tidy". Larry W4CSC |
SSB Antenna connection
"Meindert Sprang" wrote in
: Indeed, it will radiate as much as the antenna does. Therefore it is best to place the ATU immediately at the feed point of the backstay. The best practical place would be directly below deck, underneath the backstay. Every effort to keep the GTO15 as short as possible is best. Meindert Where'd this "high voltage neon wire" nonsense come from? The tiny wire inside there is way too small for when the 50' backstay nears 1/4 wavelength at 5 Mhz where its impedance will be REALLY LOW and its antenna current at 150 watts will be REALLY HIGH.....SAY 15 OHMS and THREE amps! There are many frequencies at which the impedance of any sailboat backstay antenna is LOW, not high! around 5-6 Mhz, around 15-16 Mhz where it becomes 3/4 wavelength resonant. I don't like this thin high voltage wire idea. Lionheart has a 8" piece of #10 copperweld antenna wire connecting her AT-150 tuner to the base of the backstay. This makes 40 meters just work fantastic with a good ground on 7 Mhz where the antenna's complex impedance is still very low. 73, Larry W4CSC Sigs 5/8 to 9 in Moldova, Moscow, Czech Republic, Brazil on 7 and 14 Mhz ham bands. Great fun working DX from Florida from the backstay. |
SSB Antenna connection
The central conductor of GTO15 isn;t all that thin. Seems to work
well and also seems to be the standard fopr the purpose. I'm not sure what neon wire looks like. Doug, k3qt s/v Callista "Larry W4CSC" wrote in message ... "Meindert Sprang" wrote in : Indeed, it will radiate as much as the antenna does. Therefore it is best to place the ATU immediately at the feed point of the backstay. The best practical place would be directly below deck, underneath the backstay. Every effort to keep the GTO15 as short as possible is best. Meindert Where'd this "high voltage neon wire" nonsense come from? The tiny wire inside there is way too small for when the 50' backstay nears 1/4 wavelength at 5 Mhz where its impedance will be REALLY LOW and its antenna current at 150 watts will be REALLY HIGH.....SAY 15 OHMS and THREE amps! There are many frequencies at which the impedance of any sailboat backstay antenna is LOW, not high! around 5-6 Mhz, around 15-16 Mhz where it becomes 3/4 wavelength resonant. I don't like this thin high voltage wire idea. Lionheart has a 8" piece of #10 copperweld antenna wire connecting her AT-150 tuner to the base of the backstay. This makes 40 meters just work fantastic with a good ground on 7 Mhz where the antenna's complex impedance is still very low. 73, Larry W4CSC Sigs 5/8 to 9 in Moldova, Moscow, Czech Republic, Brazil on 7 and 14 Mhz ham bands. Great fun working DX from Florida from the backstay. |
SSB Antenna connection
Normally, when tywrapping the feedline to the backstay below
the insulator, the lower part of the backstay is not grounded. Otherwise small standoff are used. Doug. k3qt s/v Callista "Larry W4CSC" wrote in message ... "Meindert Sprang" wrote in : Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of about 200 ohms at 4 MHz) does to a high impedance (several kOhms at 4MHz) antenna connection: right... almost short circuit it to ground. NEVER use coax between the ATU and the antenna. That's just about as bad as neatly tywrapping the wire from the tuner to the bottom insulator on the backstay to the grounded backstay part UNDER the bottom insulator. Trying to get them to let that wire HANG away from everything to lower the capacitance to ground is like trying to get 5200 adhesive that's hardened out of a crack in the decking. They don't care what it does to the signal output, as long as it looks "neat and tidy". Larry W4CSC |
SSB Antenna connection
In article ,
"Doug Dotson" wrote: Normally, when tywrapping the feedline to the backstay below the insulator, the lower part of the backstay is not grounded. Otherwise small standoff are used. Doug. k3qt s/v Callista "Larry W4CSC" wrote in message ... "Meindert Sprang" wrote in : Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of about 200 ohms at 4 MHz) does to a high impedance (several kOhms at 4MHz) antenna connection: right... almost short circuit it to ground. NEVER use coax between the ATU and the antenna. That's just about as bad as neatly tywrapping the wire from the tuner to the bottom insulator on the backstay to the grounded backstay part UNDER the bottom insulator. Trying to get them to let that wire HANG away from everything to lower the capacitance to ground is like trying to get 5200 adhesive that's hardened out of a crack in the decking. They don't care what it does to the signal output, as long as it looks "neat and tidy". Larry W4CSC I liked the idea, I saw here a while back, of using the new Kevlar based Backstay material, and not worring about having to ground or not. Seemed like the logical answer to me. Then just helical wrap the antenna wire around the Kevlar Backstay and have a really nice "Fully Loaded Antenna with alot of electrical length........ Bruce in alaska -- add a 2 before @ |
SSB Antenna connection
On Thu, 3 Jun 2004 14:56:44 -0400, "Jack Painter"
wrote: Bruce, you're making a totally off the wall argument now, with opposite assumptions that were never asserted or offered by any of the posters to this thread. Taking your questions literally as you phrased them would generate a laugh by all, indeed. If a laugh was your intention, we'll all have a good one. But I doubt that you are confused about skin effect, or why a faraday cage works, and specifically what would defeat it's protection (ie: an opening). So if you seriously think that for instance, a c-clamp applied across an open end of thin walled copper tubing, contacting the inner and outer wall in it's grip, would apply voltage differently to the inside versus the outside of this tubing, then it will be easy to explain your error in thinking. And since I did not make a joke of your obvious geometry and math errors in determining the surface area of an object, one which you continue to be confused about, I would suggest that we either: end the thread if you do not desire pleasant and professional discussion, or, omitting the snide comments that do not reflect well on the group or it's interested participants. Respectfully, Jack Painter Virginia Beach, Va Oh boy! I just got back from vacation and am just now reading this stuff. Jack, Bruce and the others are entirely right. I once had a hard time figuring out why RF would not flow on the inside of a tube too. It would seem logical that it would do as you say but it doesn't. Look up "wave guide beyond cutoff". That will answer your question about why rf dose not flow on the inside of a tube. It will flow on the inside for only a very short distance from the opening. Then it gets canceled. This is how many signal generator attenuater work. They use a tube of 6 or so inches long with a sliding probe inside fed from one end. On the other open end is a fixed pickup probe. When the movable probe is close to the fixed probe on the other end, maximum signal coupling is obtained. As the other probe is moved away inside the tube the signal becomes highly attenuated. It is operating as a wave guide that is much too small for the frequency involved. If the tube diameter was made large enough to be a quarter wave length in diameter then the rf would propagate through it. But that would be in a different mode than the skin effect conduction being discussed. By the way did you know that skin effect even comes into play in 60 hz distribution systems? Regards Gary |
SSB Antenna connection
On Wed, 26 May 2004 11:38:26 -0400, "Jack Painter"
wrote: "Steve (another one)" wrote in message ... Dear Folks, What is the recommended wire to connect my insulated backstay to my AT-120 tuner ? I see references to GTO15 for this purpose in American publications, but no-one here in the UK seems to know what GTO15 is. Could someone please suggest an equivalent, or at least a description ! Also if the ground connection has to be broad copper strip because RF won't run down a wire like a conventional dc current, how can the antenna be wire ? Doesn't RF have to run along the cable to the base of the antenna and then up the antenna wire itself ? I'm confused ! Thanks for your help. Steve Steve, you have asked about two distinctly different forms of connection that require equally different conductors. Additionally, within your grounding questions there also are two different issues, addressed below: 1. RF feedline from ATU to antenna. This should be coaxial cable with dialectric and shielding designed for RF. Never improvise with something such as spark plug wires. 2.(a) Grounding: RF This does not have to be wide surface area copper, but doing so will not hurt, and it will allow the combination-use of the RF ground connection to serve as a lightning protection ground. RF ground does not require a dc- connection to ground, and is often designed to use capacitive coupling to ground for sailing vessels and other marine applications where isolation for galvanic protection is adviseable. 2. (b) Grounding: Lightning protection Also does not require a dc-connection to ground, but may not use low valued capacitors such as would be acceptable for RF ground. Lightning protection DOES require the widest surface area possible, this provides a lower impedance path to ground. But your radio and auto-tuner and other equipment are most importantly bonded to each other, and that may be of any standard braid, #8 wire, etc. Only the single connection of all your bonded equipment to ship's ground must be of the highest surface area possible. If more than one connection from bonded equipment to ground must be made, then each of those connections should be wide surface area conductors. Hope this helps, Jack Painter Virginia Beach, VA A good lightning ground is also a good RF ground. But a good RF ground is not always a good lightning ground. (as in the case of elevated radials) Most lightning energy is concentrated in the DC to 1 mhz range with some energy going much higher in frequency. So the ground conductors and ground system must be treated the same as an RF ground system with with regard to low impedance leads (large surface area) and, in the case of lightning, low DC resistance connections. Even a low resistance connection can develop many thousands of volts across it with the high current lightning. An RF ground requires a low impedance conductor as well. Regards Gary |
SSB Antenna connection
On Wed, 26 May 2004 03:42:24 GMT, Bruce in Alaska
wrote: In article , "Steve (another one)" wrote: Dear Folks, What is the recommended wire to connect my insulated backstay to my AT-120 tuner ? I see references to GTO15 for this purpose in American publications, but no-one here in the UK seems to know what GTO15 is. Could someone please suggest an equivalent, or at least a description ! Also if the ground connection has to be broad copper strip because RF won't run down a wire like a conventional dc current, how can the antenna be wire ? Doesn't RF have to run along the cable to the base of the antenna and then up the antenna wire itself ? I'm confused ! Thanks for your help. Steve Others have covered the GTO-15 question, very well. There are a number of reasons that copper strap is used for RF Grounding in the Maritime Radio Installations. One being, that it is desireable for the RF Ground to have the lowest possible Impedance at the transmitted frequency. Two being, that it is desirable that the surface area of the RF Ground System be as large as practicable, to maximise coupling to the seawater. Three being, That RF flows on the surface of the conductor, and more surface area means lower impedance on the Ground. The antenna wire isn't supposed to couple into the seawater, but into the ethos, so it should have the least surface area as can practically handle the RF Current of the transmitter and be tuned to resonance by the tuner, and as low of resistance as practicable, so that RF Current can propagate along it's length. Bruce in alaska Gary S. can chime in anytime on this..... Hi Bruce, The diameter of the antenna wire is not too important. Actually the larger it is the less resistive loss it has and less power will be wasted in heat. But unless the antenna is significantly shorter than a quarter wavelength that loss is negligible in the antenna as the radiation resistance (radiation resistance is where the power goes to be radiated) is usually much higher than the resistive loss of the wire. However in a very short antenna the radiation resistance can be only an ohm or a few ohms. Then the resistance of the wire would be a larger percentage and the heat loss would be greater thus warranting a larger diameter wire. Otherwise a larger diameter wire has the advantage of greater bandwidth for given tuner settings. But the difference between #10 and # 16 would probably not be noticeable. As you well know, in the case of the ground system as we have said many times before, it needs to be as short as possible or it becomes part of the antenna and radiates. "The antenna starts at ground". Anything above ground is antenna. Regards Gary |
SSB Antenna connection
On Fri, 28 May 2004 19:10:14 -0400, "Jack Painter"
wrote: "Chuck" wrote in message ... Bruce, I am asking why there is apparently such difference between feeding an ungrounded dipole with coax from an ATU (my shore station) and feeding an insulated (hence ungrounded) backstay from an ATU? I work Alaska bareback in the summertime with that setup and I just can't understand what GTO-15 does that hardline doesn't. If you could explain or reference a document that specifies the reasoning I would try to correct my misunderstanding. Thanks, Jack Painter Virginia Beach, Va If I can jump in, the quick answer is that the coax is approximately the same impedance as the center of your ungrounded dipole, at least at the frequency for which it is resonant. Thus, from the perspective of the transmitter and the antenna, the transmission line is "invisible." I'm exaggerating, of course. In the case of a backstay used as an antenna, the feedpoint impedance can be anywhere from a small fraction of an ohm at low frequencies to thousands of ohms where it approximates a half-wavelength. In those cases, the coax will most certainly not be invisible and will most likely either burn up or greatly attenuate your signal (incoming as well as outgoing, actually). If you tried to end-feed your half-wavelength dipole with coax, you would see a similar problem because the impedance at the ends is in the thousands of ohms range. Hope that helps. Chuck, as with Meindert's answer, yes that helps, thank you. I do end-feed a long wire as I said earlier, but it uses a 4:1 Balun, and additionally, has one side of that Balun shorted to ground. This is a noise-limiting design, and while the nice folks at Radio Works (Portsmouth, Va) maintain that it cannot possibly work this way (their Baluns), the CG aircraft I worked in Ecuador with it thought otherwise. So does it's designer, whose name slips my mind at the moment but he was a primary contributer to "Proceedings", and a Phd in EE with many patented antenna designs. Anyway, it would be interesting to see some modelling done with backstay antennas using various feedline approaches. I suspect the difference varies greatly with wavelength, height above ground (water), angle, and frequency. 73, Jack Painter Virginia Beach, Va Jack, Using a balun to feed an end fed wire may help and it may hurt the situation. It depends on the length of the wire verses frequency. If the wavelength is greater than a quarter wave length and the impedance of the wire is high, the balun will transform it down to a sometimes easier to match impedance. However if you use the antenna on different bands and you chose a band where the impedance of the antenna is low, then the 4:1 balun will step the impedance down even lower than the already low impedance of the antenna. It may well be that it is too low to match efficiently. As a general rule that type of balun is not a good idea when using that type of antenna on multiple bands. The only good a 1:1 balun would do with that type of antenna would be to decouple the feed line from the antenna (assuming coax feed line) and keep the feed line from radiating and or picking up unwanted signals. Regards Gary |
SSB Antenna connection
I am the one who posted that idea. I implemented it and used the setup on a
recent Mexico trip. I am a newbie in this arena, so I can only tell you that my rig was probably the best in the fleet of several boats. On the subject of antenna feed wire, I found an old reference on this NG recommending stripping the braid from coax(RG-8 is what I used) as a substitute for GTO-15. I was unable to locate a local source for GTO-15, so I went with the stripped coax. I was unable to do a good job on standoffs for the coax because of the hydraulics, but it didn't seem to matter a great deal. I did not think to do a helical wrap of the antenna wire which incidentally was just standard insulated #16 Ancor about 45' in length. On larger boats, the antenna wire is buried beneath the UV shield; on mine the wire was taped to the exterior of the UV shield. A lot of racing sailboats are switching their rod or wire backstays to Aramid at this time. The weight savings is dramatic, and the cost is roughly half of what a backstay with insulators would cost. I liked the idea, I saw here a while back, of using the new Kevlar based Backstay material, and not worring about having to ground or not. Seemed like the logical answer to me. Then just helical wrap the antenna wire around the Kevlar Backstay and have a really nice "Fully Loaded Antenna with alot of electrical length........ Bruce in alaska -- add a 2 before @ |
SSB Antenna connection
"Gary Schafer" wrote
Oh boy! I just got back from vacation and am just now reading this stuff. Jack, Bruce and the others are entirely right. I once had a hard time figuring out why RF would not flow on the inside of a tube too. It would seem logical that it would do as you say but it doesn't. Look up "wave guide beyond cutoff". That will answer your question about why rf dose not flow on the inside of a tube. It will flow on the inside for only a very short distance from the opening. Then it gets canceled. This is how many signal generator attenuater work. They use a tube of 6 or so inches long with a sliding probe inside fed from one end. On the other open end is a fixed pickup probe. When the movable probe is close to the fixed probe on the other end, maximum signal coupling is obtained. As the other probe is moved away inside the tube the signal becomes highly attenuated. It is operating as a wave guide that is much too small for the frequency involved. If the tube diameter was made large enough to be a quarter wave length in diameter then the rf would propagate through it. But that would be in a different mode than the skin effect conduction being discussed. By the way did you know that skin effect even comes into play in 60 hz distribution systems? Regards Gary Hi Gary, welcome back, and thanks for your replies. Right principles, wrong application. Trying to apply high power microwave principles (3-15 gHz) to low power 2-30 mHz) is not the same. Now at 100 mHz and below, while there would still a small but measurable difference of skin effect at high transmit power, it ain't much and has nothing to do with low power 2-30 mHz where a thin walled copper tube has ZERO measurable difference in skin effect to a copper strap of even slightly smaller gage. That has been my never paid attention to point all along, that skin effect involves the entire cross section of thin material, and copper tubing is more than thin enough to carry current in it's entire (that means from outer to inner surface) cross section. That's exactly why copper tube is used so much in AM broadcast components. This is not even related to waveguides which must by design AVOID all skin effect which causes great resistance and heating at the current and velocites involved in microwave transmission. As we eventually got around to research rather than blindly arguing positions of opinion, then the participants hopefully learned something. I've learned that applying the math from formulas for skin effect in conductors of known ohmic value and used with a known frequency can determine the wall thickness of a conductor which has full cross sectional current on it. Guess what? The original poster's question about using copper tubing remains answered. A 1" copper tube has more surface area and carries just as much low power RF on it's entire cross section as a 1" wide piece of copper strap that is nearly the same gage. Best, Jack Painter Virginia Beach Va |
SSB Antenna connection
Bruce in Alaska wrote in
: Hmmmm, all the PhdEE's that I asked, just laughed and ask how the weather and fishing was......... Bruce in alaska While you PhdEE's are on a roll, a little question...... A 6" wide, 1" thick solid copper strap 20 ft long connects an antenna tuner at the base of a 58' 3" insulated backstay on deck to a 30' long, 6" wide grounding block under the keel of a boat. What ground impedance does the tuner see on the 12 Mhz band? Larry W4CSC |
SSB Antenna connection
Gary Schafer wrote in
: A good lightning ground is also a good RF ground. Welcome home, Gary. Missed your dissertations, really. Ah, but once again, BZZZT...WRONG..... I got two real-world examples to show you from my Navy experiences...... 1 - Aboard a wooden MSO (minesweeper, ocean), a sailor was nearly burned alive when he touched a metal handrail just outside the bridge while on watch! His hands had bad burns, as did his hip, which was touching a pipe not connected to the handrail. An electrical inspection found the handrail heavily grounded, per Navy requirements, to the boat's electrical grounding system, a good installation with no problems found. However, the burning continued. I found out about it from the boat's ET gang because I was in MINELANT's Mine Force Support Group electronics shop, at the time, around 1970? My EMO asked me my opinion and for me to take a look. Not far from the handrail was the antenna tuner and 35' whip of the boat's AN/URC-32 500W HF transmitter. Curious, I got a list of the frequencies the boat transmitted on the day he got burned. They operated only three that day, all on RTTY (FSK at full power). I took a tape measure and, as best we could, measured the length of the ground strap down into the bilge where it connected to the ship's grounding system. It was around 31 feet, total length, and didn't really connect to any other points on the way down into the engine room. One of the frequencies in question was on the 4 Mhz band just above the 75 meter ham band. At this frequency, the 31' ground strap was quite close to a 1/4 wavelength resonant ANTENNA with the open end right under our burned sailor's forearm and coffee cup he threw when the FSK started. So, let's test this theory. I took a scope probe with a 6' ground lead on it and connected the scope between the pipe he was leaning against, itself some length of antenna at some other frequency, and our burning handrail. "Key the transmitter.", I called down the passageway. WOW! The trace of the 4 Mhz RF was TOO BIG TO MEASURE! I could feel the RF in my fingers! So, moral, this great lightning ground was NOT ANYWHERE NEAR a good RF ground on 4 Mhz, or any other odd multiple of 1/4 wavelength. It was a resonant antenna with a handrail capacitor hat waiting to bite someone! Solution - After months of fighting the electrical engineers at NAVSEA about SHIPALTs to allow us to install them, we finally won and installed RF Chokes into all handrail grounds at the handrails themselves to keep them from becoming antennas resonant at any HF freq the ship used. 2 - Charleston Naval Shipyard, Metrology Laboratory of the Quality Assurance Office (Code 132.1). I was asked to look at a crazy alarm problem at the nuclear refueling docks where we pulled out the reactors from nuclear subs and replaced them with refuelled reactors. (The hulls are cut open and the core is swapped by a specially-equipped huge crane that runs on big rail tracks around the docks). Every time the crane lowered its big hook down into the hull, all the radiation alarms went crazy, even before the hook got to where it was supposed to go! Electrical Engineers (not RF engineers by a long shot) added more and more ground straps between the rails the huge crane sat on and the hull of the sub to "make sure" we had a "good ground" on everything. (More grounds were always their answer to everything.) I made arrangements to get the crane to where it would normally operate, with the operator at the controls, but with the hook first hanging over the rail of the crane, then over the hull of the sub in the drydock for testing. I snatched a portable Tektronix scope from the shop's inventory that was battery powered so it wouldn't be part of the grounding systems and met the crane at the appropriate time. I grounded the scope to the track at a handy pad eye used to hook the sub ground to it and as I approached this huge steel hook the trace on the scope went off my screen. My AC voltmeter read over 80VAC between "ground" and that hook. But wait! What's this MODULATION all about?? I ran back to the shop to retrieve my portable radio and quickly returned to the test point. Watching the AM modulation on my scope while tuning around on the AM band, I matched up the modulation envelope with WNCG AM 910Khz, a 5KW AM radio station some IDIOT at the FCC allowed them to construct right outside the hospital gate less than a mile from where I was standing. THE CRANE WAS A GIANT LOOP ANTENNA and I was standing at the high-impedance FEEDPOINT of that loop! Identifying the problem was easy. DOING something about the problem was NOT! NOONE in Rickover's Navy makes any CHANGES to anything without a fight. This fight I left, gladly, to much higher powers than me, but it also resulted in a huge strain insulator added to the cable of the crane to INSULATE the offending signal from the hook lowered into the sub. Wonder whatever happened to it, now that it's all gone bye-bye....?? Moral....a great lightning or AC line or DC ground is hardly EVER a good RF ground..... Ok, as usual, your turn..... Larry |
SSB Antenna connection
Gary Schafer wrote in
: The diameter of the antenna wire is not too important. Actually the larger it is the less resistive loss it has and less power will be wasted in heat. But unless the antenna is significantly shorter than a quarter wavelength that loss is negligible in the antenna as the radiation resistance (radiation resistance is where the power goes to be radiated) is usually much higher than the resistive loss of the wire. The diameter of the antenna wire is very important in the antenna's BANDWIDTH. Go by the CG shore station and look at how WIDE the conical monopole antenna is: http://www.tpub.com/content/et/14092/css/14092_35.htm The whole reason for the wide cone of these broadband HF antennas is to make it look as if the conductor were several FEET across to the RF from the feedpoint. Multiple, parallel conductors are also used to increase antenna wire apparent diameter in broadband rhombic antennas such as: http://www.smc-comms.com/rhombic_antenna.htm To quote the text: "The simple one wire system has a bandwidth of approximately 2: 1, however SMC have wide experience in the design of this type of antenna and are able to offer arrays with 1, 2 or 3 wires per leg to give a bandwidth of up to 4: 1 and, by careful design, gains of 22 dBi are possible." However in a very short antenna the radiation resistance can be only an ohm or a few ohms. Then the resistance of the wire would be a larger percentage and the heat loss would be greater thus warranting a larger diameter wire. Huh?? ANY antenna under 1/4 wavelength long exhibits HIGHER and HIGHER impedance the SHORTER it gets. The first low impedance of a wire antenna occurs when its radiator (against a ground, artificial or real) is 1/4 wavelength long. A very short antenna, i.e. a 6' whip on the handrail, has a very HIGH impedance as frequency decreases on the HF band. That's why we use an L network to match it to 50 ohms....coil in series, cap to ground to lower its impedance. Otherwise a larger diameter wire has the advantage of greater bandwidth for given tuner settings. But the difference between #10 and # 16 would probably not be noticeable. True, that's why we use multiple parallel conductors above. As you well know, in the case of the ground system as we have said many times before, it needs to be as short as possible or it becomes part of the antenna and radiates. "The antenna starts at ground". Anything above ground is antenna. Actually, in a plastic boat, the radiation from the ground strap is useful radiation. You've just moved the FEEDPOINT up the radiating element above the sea. My feedpoint is about 4.8' above ground on Lionheart. It's signal strength 5, readability 8 in Moscow, Belarus, UAE, Japan, Brazil, most of Western Europe on 40 meters and 20 meters. Works pretty good! 73, Larry W4CSC |
SSB Antenna connection
On Tue, 8 Jun 2004 17:05:53 -0400, "Jack Painter" wrote: "Gary Schafer" wrote Oh boy! I just got back from vacation and am just now reading this stuff. Jack, Bruce and the others are entirely right. I once had a hard time figuring out why RF would not flow on the inside of a tube too. It would seem logical that it would do as you say but it doesn't. Look up "wave guide beyond cutoff". That will answer your question about why rf dose not flow on the inside of a tube. It will flow on the inside for only a very short distance from the opening. Then it gets canceled. This is how many signal generator attenuater work. They use a tube of 6 or so inches long with a sliding probe inside fed from one end. On the other open end is a fixed pickup probe. When the movable probe is close to the fixed probe on the other end, maximum signal coupling is obtained. As the other probe is moved away inside the tube the signal becomes highly attenuated. It is operating as a wave guide that is much too small for the frequency involved. If the tube diameter was made large enough to be a quarter wave length in diameter then the rf would propagate through it. But that would be in a different mode than the skin effect conduction being discussed. By the way did you know that skin effect even comes into play in 60 hz distribution systems? Regards Gary Hi Gary, welcome back, and thanks for your replies. Right principles, wrong application. Trying to apply high power microwave principles (3-15 gHz) to low power 2-30 mHz) is not the same. Sorry Jack but you are wrong. It has nothing to do with microwave frequencies. A wave guide beyond cutoff is the mode that the tube is operating in and it simply tells you that the frequency is too low for the given size tube to propagate through. The energy inside the tube gets shorted out. Many 2-30 mhz signal generators use that type attenuator. Now at 100 mHz and below, while there would still a small but measurable difference of skin effect at high transmit power, it ain't much and has nothing to do with low power 2-30 mHz where a thin walled copper tube has ZERO measurable difference in skin effect to a copper strap of even slightly smaller gage. It has everything to do with it. Skin effect is ever present in all conductors at ALL frequencies. Note my reference to 60 hz power transmission where it is also important. That has been my never paid attention to point all along, that skin effect involves the entire cross section of thin material, and copper tubing is more than thin enough to carry current in it's entire (that means from outer to inner surface) cross section. That's exactly why copper tube is used so much in AM broadcast components. That is a contradiction to your point. You say that current flows entirely through the walls of copper tubing and then say that is why it is used in AM broadcast components. If that were true then they would not use copper tubing but instead they would use solid copper rod for better conduction. The reason copper tubing is used is that there is no current of any significance past a certain depth and to use solid rod would be a waste of copper. This is not even related to waveguides which must by design AVOID all skin effect which causes great resistance and heating at the current and velocites involved in microwave transmission. Well, microwave transmissions don't travel any faster than HF transmissions. But you might note that most wave guide inner surfaces are silver plated to reduce skin losses. As we eventually got around to research rather than blindly arguing positions of opinion, then the participants hopefully learned something. I've learned that applying the math from formulas for skin effect in conductors of known ohmic value and used with a known frequency can determine the wall thickness of a conductor which has full cross sectional current on it. Guess what? The original poster's question about using copper tubing remains answered. A 1" copper tube has more surface area and carries just as much low power RF on it's entire cross section as a 1" wide piece of copper strap that is nearly the same gage. While skin effect is a gradient and not an absolute barrier, there is current that flows at all levels in a conductor. Even on the inner surface of your copper tube. But the amount of current there is so small that it is immeasurable. It decreases exponentially. One skin depth is defined as the depth at which the current has dropped to about .37 times the current at the surface. (If you notice, this is the same decay rate that a capacitor has when it charges or discharges.) When you go that same distance (deeper) again the remaining current will again drop to .37 times the current that it was at the first skin depth. So you can see that the current never reaches zero as you go deeper but it only takes a few skin depths to decrease the current to a very small value which is insignificant. ..0058" is the skin depth in copper at 200 khz. Skin depth decreases by 10 for each 100 times increase in frequency. So at 20 mhz the skin depth would decrease by 100 from that. It gets pretty thin! Skin effect is the reason coax cable works as it does. None of the RF on the inside of the cable appears on the outside of the cable. Other than leakage between strands of the shield of the cable. Those wire strands on coax cable are pretty thin. Much thinner than your copper pipe. Hard line has no leakage. Regards Gary Best, Jack Painter Virginia Beach Va |
SSB Antenna connection
On Tue, 08 Jun 2004 23:39:09 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : A good lightning ground is also a good RF ground. Welcome home, Gary. Missed your dissertations, really. Ah, but once again, BZZZT...WRONG..... I got two real-world examples to show you from my Navy experiences...... 1 - Aboard a wooden MSO (minesweeper, ocean), a sailor was nearly burned alive when he touched a metal handrail just outside the bridge while on watch! His hands had bad burns, as did his hip, which was touching a pipe not connected to the handrail. An electrical inspection found the handrail heavily grounded, per Navy requirements, to the boat's electrical grounding system, a good installation with no problems found. However, the burning continued. I found out about it from the boat's ET gang because I was in MINELANT's Mine Force Support Group electronics shop, at the time, around 1970? My EMO asked me my opinion and for me to take a look. Not far from the handrail was the antenna tuner and 35' whip of the boat's AN/URC-32 500W HF transmitter. Curious, I got a list of the frequencies the boat transmitted on the day he got burned. They operated only three that day, all on RTTY (FSK at full power). I took a tape measure and, as best we could, measured the length of the ground strap down into the bilge where it connected to the ship's grounding system. It was around 31 feet, total length, and didn't really connect to any other points on the way down into the engine room. One of the frequencies in question was on the 4 Mhz band just above the 75 meter ham band. At this frequency, the 31' ground strap was quite close to a 1/4 wavelength resonant ANTENNA with the open end right under our burned sailor's forearm and coffee cup he threw when the FSK started. So, let's test this theory. I took a scope probe with a 6' ground lead on it and connected the scope between the pipe he was leaning against, itself some length of antenna at some other frequency, and our burning handrail. "Key the transmitter.", I called down the passageway. WOW! The trace of the 4 Mhz RF was TOO BIG TO MEASURE! I could feel the RF in my fingers! So, moral, this great lightning ground was NOT ANYWHERE NEAR a good RF ground on 4 Mhz, or any other odd multiple of 1/4 wavelength. It was a resonant antenna with a handrail capacitor hat waiting to bite someone! Solution - After months of fighting the electrical engineers at NAVSEA about SHIPALTs to allow us to install them, we finally won and installed RF Chokes into all handrail grounds at the handrails themselves to keep them from becoming antennas resonant at any HF freq the ship used. 2 - Charleston Naval Shipyard, Metrology Laboratory of the Quality Assurance Office (Code 132.1). I was asked to look at a crazy alarm problem at the nuclear refueling docks where we pulled out the reactors from nuclear subs and replaced them with refuelled reactors. (The hulls are cut open and the core is swapped by a specially-equipped huge crane that runs on big rail tracks around the docks). Every time the crane lowered its big hook down into the hull, all the radiation alarms went crazy, even before the hook got to where it was supposed to go! Electrical Engineers (not RF engineers by a long shot) added more and more ground straps between the rails the huge crane sat on and the hull of the sub to "make sure" we had a "good ground" on everything. (More grounds were always their answer to everything.) I made arrangements to get the crane to where it would normally operate, with the operator at the controls, but with the hook first hanging over the rail of the crane, then over the hull of the sub in the drydock for testing. I snatched a portable Tektronix scope from the shop's inventory that was battery powered so it wouldn't be part of the grounding systems and met the crane at the appropriate time. I grounded the scope to the track at a handy pad eye used to hook the sub ground to it and as I approached this huge steel hook the trace on the scope went off my screen. My AC voltmeter read over 80VAC between "ground" and that hook. But wait! What's this MODULATION all about?? I ran back to the shop to retrieve my portable radio and quickly returned to the test point. Watching the AM modulation on my scope while tuning around on the AM band, I matched up the modulation envelope with WNCG AM 910Khz, a 5KW AM radio station some IDIOT at the FCC allowed them to construct right outside the hospital gate less than a mile from where I was standing. THE CRANE WAS A GIANT LOOP ANTENNA and I was standing at the high-impedance FEEDPOINT of that loop! Identifying the problem was easy. DOING something about the problem was NOT! NOONE in Rickover's Navy makes any CHANGES to anything without a fight. This fight I left, gladly, to much higher powers than me, but it also resulted in a huge strain insulator added to the cable of the crane to INSULATE the offending signal from the hook lowered into the sub. Wonder whatever happened to it, now that it's all gone bye-bye....?? Moral....a great lightning or AC line or DC ground is hardly EVER a good RF ground..... Ok, as usual, your turn..... Larry Hi Larry, Hope you had a good sail. Well this is an easy one! Your hand rail was not a good lightning ground even though it may have had a large ground strap connected to it. The path to ground was too long providing a high impedance. Same for the crane. Too long a ground lead at the hook. A good lightning ground has to have a low DC resistance as well as a low impedance to AC. Remember that lightning has a large AC component that is very strong. Any impedance in it's path despite how well the DC ground may be will allow a large voltage to develop on it. A good antenna ground must also have a low impedance. Regards Gary |
SSB Antenna connection
I'm having trouble imaging a 6" wide by 1" thick piece of
copper as a "strap" :) Doug, k3qt s/v Callista "Larry W4CSC" wrote in message ... Bruce in Alaska wrote in : Hmmmm, all the PhdEE's that I asked, just laughed and ask how the weather and fishing was......... Bruce in alaska While you PhdEE's are on a roll, a little question...... A 6" wide, 1" thick solid copper strap 20 ft long connects an antenna tuner at the base of a 58' 3" insulated backstay on deck to a 30' long, 6" wide grounding block under the keel of a boat. What ground impedance does the tuner see on the 12 Mhz band? Larry W4CSC |
SSB Antenna connection
On Wed, 09 Jun 2004 00:00:34 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : The diameter of the antenna wire is not too important. Actually the larger it is the less resistive loss it has and less power will be wasted in heat. But unless the antenna is significantly shorter than a quarter wavelength that loss is negligible in the antenna as the radiation resistance (radiation resistance is where the power goes to be radiated) is usually much higher than the resistive loss of the wire. The diameter of the antenna wire is very important in the antenna's BANDWIDTH. Go by the CG shore station and look at how WIDE the conical monopole antenna is: http://www.tpub.com/content/et/14092/css/14092_35.htm The whole reason for the wide cone of these broadband HF antennas is to make it look as if the conductor were several FEET across to the RF from the feedpoint. Multiple, parallel conductors are also used to increase antenna wire apparent diameter in broadband rhombic antennas such as: http://www.smc-comms.com/rhombic_antenna.htm To quote the text: "The simple one wire system has a bandwidth of approximately 2: 1, however SMC have wide experience in the design of this type of antenna and are able to offer arrays with 1, 2 or 3 wires per leg to give a bandwidth of up to 4: 1 and, by careful design, gains of 22 dBi are possible." However in a very short antenna the radiation resistance can be only an ohm or a few ohms. Then the resistance of the wire would be a larger percentage and the heat loss would be greater thus warranting a larger diameter wire. Huh?? ANY antenna under 1/4 wavelength long exhibits HIGHER and HIGHER impedance the SHORTER it gets. The first low impedance of a wire antenna occurs when its radiator (against a ground, artificial or real) is 1/4 wavelength long. A very short antenna, i.e. a 6' whip on the handrail, has a very HIGH impedance as frequency decreases on the HF band. That's why we use an L network to match it to 50 ohms....coil in series, cap to ground to lower its impedance. Otherwise a larger diameter wire has the advantage of greater bandwidth for given tuner settings. But the difference between #10 and # 16 would probably not be noticeable. True, that's why we use multiple parallel conductors above. As you well know, in the case of the ground system as we have said many times before, it needs to be as short as possible or it becomes part of the antenna and radiates. "The antenna starts at ground". Anything above ground is antenna. Actually, in a plastic boat, the radiation from the ground strap is useful radiation. You've just moved the FEEDPOINT up the radiating element above the sea. My feedpoint is about 4.8' above ground on Lionheart. It's signal strength 5, readability 8 in Moscow, Belarus, UAE, Japan, Brazil, most of Western Europe on 40 meters and 20 meters. Works pretty good! 73, Larry W4CSC Oh oh, here we go again. :) Remember I said that the radiation resistance drops as the antenna gets shorter. That is the reason the losses go up with a shorter antenna. Higher current in the antenna and loading coil means more I squared R loss. (radiation resistance is equal to the equivalent resistor that would dissipate the same amount of power that is being radiated) Lower radiation resistance requires more current for the same amount of power verses a higher radiation resistance and less current. The reactance does indeed get higher the shorter the antenna is. With an antenna shorter than a quarter wave length as you know it looks like a capacitor. (capacitive reactance) The less capacitance (shorter antenna) the higher the reactance. The coil in series provides an equal but opposite inductive reactance to cancel the capacitive reactance in the antenna. That leaves only the radiation resistance to feed power to. The coil AC resistance (not reactance now)is then effectively in series with the radiation resistance of the antenna. The same current must flow in both the antenna and coil losses. While the antenna radiates most of the power it gets, the coil dissipates power in heat equal to the I squared R loss in the coil. The capacitor to ground on the other side of the coil and part of the coil form an L network to match the impedance to the feed line. Actually we could say that the L network portion really matches the radiation resistance plus the coil resistance to the feed line. Because when the coil reactance and antenna reactance are equal we have resonance and the only component left is purely resistive. The high reactance in the antenna causes the voltage to go high. But there is also a phase shift due to the reactance. So the current is not in phase with the voltage developed across the reactance. That is why the voltage is high. Regards Gary |
SSB Antenna connection
In article ,
Gary Schafer wrote: Hi Bruce, The diameter of the antenna wire is not too important. Actually the larger it is the less resistive loss it has and less power will be wasted in heat. But unless the antenna is significantly shorter than a quarter wavelength that loss is negligible in the antenna as the radiation resistance (radiation resistance is where the power goes to be radiated) is usually much higher than the resistive loss of the wire. However in a very short antenna the radiation resistance can be only an ohm or a few ohms. Then the resistance of the wire would be a larger percentage and the heat loss would be greater thus warranting a larger diameter wire. Otherwise a larger diameter wire has the advantage of greater bandwidth for given tuner settings. But the difference between #10 and # 16 would probably not be noticeable. As you well know, in the case of the ground system as we have said many times before, it needs to be as short as possible or it becomes part of the antenna and radiates. "The antenna starts at ground". Anything above ground is antenna. Regards Gary Yep, absolutly right Gary. Bruce in alaska -- add a 2 before @ |
SSB Antenna connection
This topic is interesting. I've seen a lot of opinions expressed,
some pretty startingly. Can you posters to this thread provide some math and/or references? Thanks, Norm B |
SSB Antenna connection
"Gary Schafer" wrote
On Tue, 8 Jun 2004 17:05:53 -0400, "Jack Painter" wrote: "Gary Schafer" wrote Look up "wave guide beyond cutoff". That will answer your question about why rf dose not flow on the inside of a tube. Right principles, wrong application. Trying to apply high power microwave principles (3-15 gHz) to low power 2-30 mHz) is not the same. Sorry Jack but you are wrong. It has nothing to do with microwave frequencies. A wave guide beyond cutoff is the mode that the tube is operating in and it simply tells you that the frequency is too low for the given size tube to propagate through. The energy inside the tube gets shorted out. Many 2-30 mhz signal generators use that type attenuator. Hi Gary, the difference that is relevant, I believe, is a waveguide for microwave broadcast through the inside space of the guide, and there is minmal current intentionally allowed on the waveguide. As I did explain, skin effect must be avoided in microwave and it is due to the frequencies, however it may be exploited in HF conductors which can eliminate wasted center-core weight and cost. This is because of the drastically different behavior of microwave from HF. And velocities inside a waveguide are much faster than HF on a conductor. The attenuator you are describing allows skin effect (it cannot avoid it either) but the true waveguide avoids it, with the microwave reflecting off the walls of the guide. Hams can use a tubing-shield to fox hunt in a building, but it is a stretch of the phrase to call hiding a hh in the tube a wave guide beyond cutoff. Now at 100 mHz and below, while there would still a small but measurable difference of skin effect at high transmit power, it ain't much and has nothing to do with low power 2-30 mHz where a thin walled copper tube has ZERO measurable difference in skin effect to a copper strap of even slightly smaller gage. It has everything to do with it. Skin effect is ever present in all conductors at ALL frequencies. Note my reference to 60 hz power transmission where it is also important. Sorry Gary, that is not accurate. There is none in DC and very little until VHF. It has no measureable difference to us for purposes of our discussion between copper strap and copper tube at HF. Lightning would discover a different impedance and pick the lower one, whichever that was. You or I or any of our 150w or 1,000w radio equpment cannot tell the difference. By the same math, 60hz has no skin effect for home wiring. Long, high power transmission lines do not enter into a discussion about home wiring, and neither should mircrowave or skin effect of copper tubing (which there is none) enter into discussion about an RF ground on a sailboat or other low power station. It is irrelevant between any copper conductors of similar surface area and cross section. While skin effect is a gradient and not an absolute barrier, there is current that flows at all levels in a conductor. Even on the inner surface of your copper tube. But the amount of current there is so small that it is immeasurable. It decreases exponentially. One skin depth is defined as the depth at which the current has dropped to about .37 times the current at the surface. (If you notice, this is the same decay rate that a capacitor has when it charges or discharges.) When you go that same distance (deeper) again the remaining current will again drop to .37 times the current that it was at the first skin depth. So you can see that the current never reaches zero as you go deeper but it only takes a few skin depths to decrease the current to a very small value which is insignificant. .0058" is the skin depth in copper at 200 khz. Skin depth decreases by 10 for each 100 times increase in frequency. So at 20 mhz the skin depth would decrease by 100 from that. It gets pretty thin! Please check your premises. There is no standard depth for any frequency, rather it varies drastically from one ohmic value of a given material (conductor) to another. Since we're talking about copper, it's skin depth is considered fully cross sectional at below 100 megahertz and a thickness of ..0025". At 15mhz on tubing or strap, it is using a full cross section to carry power, not stray eddy currents. Design of course uses no more than the proper combination of surface area and cross section to handle the required frequency and power. Paper thin copper tape has limited usefulness to us, because it can handle so little current, no matter how great it's surface area. Copper tape amounts to roughly 1/3 the possible skin depth for copper at HF, so it is just a cheap and poor alternative for copper strap. Thicker than that, and we would be wasting center area that would carry little current. Nobody said coax was the best conductor, it's just the most economical. ;-) Cheers, Jack |
SSB Antenna connection
"Larry W4CSC" wrote
Actually, in a plastic boat, the radiation from the ground strap is useful radiation. You've just moved the FEEDPOINT up the radiating element above the sea. My feedpoint is about 4.8' above ground on Lionheart. It's signal strength 5, readability 8 in Moscow, Belarus, UAE, Japan, Brazil, most of Western Europe on 40 meters and 20 meters. Works pretty good! Larry, we've probably had the details of this antenna system in pieces across various posts, but would you mind putting in one place here? Sounds like an intersting and well thought out setup. Thanks, Jack |
SSB Antenna connection
"Jack Painter" wrote in message
news:7exxc.5734$5B2.1970@lakeread04... Hi Gary, the difference that is relevant, I believe, is a waveguide for microwave broadcast through the inside space of the guide, and there is minmal current intentionally allowed on the waveguide. Wrong Jack. Electromagnetic waves in a waveguide are only possible when voltages and currents are present. The maximum voltage is between the two larger sides while currents flow from one side to the other. The entire field is contained inside the waveguide and therefore the inside surface must have a low resistance and is silver plated to achieve this. You can read this in any textbook on microwave transmission. As I did explain, skin effect must be avoided in microwave and it is due to the frequencies, however it may be exploited in HF conductors which can eliminate wasted center-core weight and cost. This is because of the drastically different behavior of microwave from HF. And velocities inside a waveguide are much faster than HF on a conductor. The attenuator you are describing allows skin effect (it cannot avoid it either) but the true waveguide avoids it, with the microwave reflecting off the walls of the guide. Why do you think a microwave reflects on the wall of the waveguide? Because current flows on the inside wall, which has to have the lowest resistance possible. It is all skin effect what makes a waveguide tick! Meindert |
SSB Antenna connection
"engsol" wrote
This topic is interesting. I've seen a lot of opinions expressed, some pretty startingly. Can you posters to this thread provide some math and/or references? Thanks, Norm B Norm, because acsii graphics for the formulas you requested do not display well in newsgroups, here is a collection of the formulas and text from various websites regarding skin effect: http://members.cox.net/pc-usa/station/skineffect.htm Best regards, Jack |
SSB Antenna connection
"Meindert Sprang" wrote
"Jack Painter" wrote Hi Gary, the difference that is relevant, I believe, is a waveguide for microwave broadcast through the inside space of the guide, and there is minmal current intentionally allowed on the waveguide. Wrong Jack. Electromagnetic waves in a waveguide are only possible when voltages and currents are present. The maximum voltage is between the two larger sides while currents flow from one side to the other. The entire field is contained inside the waveguide and therefore the inside surface must have a low resistance and is silver plated to achieve this. You can read this in any textbook on microwave transmission. Hi Meindert, how is that skin effect when, as you said, the currents must flow from one side to the other? Skin effect would hold currents _on_ the surface, slow them down, and reduce the reflection that is required for propagation through the guide. Why do you think a microwave reflects on the wall of the waveguide? Because current flows on the inside wall, which has to have the lowest resistance possible. It is all skin effect what makes a waveguide tick! That sounds like a contradiction (current flows from one side to the other, and current flows on the inside wall, [the latter of which would be skin effect] ), can you explain please? Thanks, Jack |
SSB Antenna connection
"Jack Painter" wrote in message
news:r_yxc.3506$K45.1736@fed1read02... Hi Meindert, how is that skin effect when, as you said, the currents must flow from one side to the other? Skin effect would hold currents _on_ the surface, slow them down, and reduce the reflection that is required for propagation through the guide. With "one side to the other" I meant from the top inside to the bottom inside, if you lay the waveguide flat on the table. The maximum voltage inside the waveguide exists between top and bottom of the inside. Of course, the current never travels from the inside to the outside of the waveguide. Below the minimum frequency of a waveguide, no energy can be transported inside the waveguide and thus no currents will flow at the inside. Meindert |
SSB Antenna connection
On Wed, 9 Jun 2004 01:28:26 -0400, "Jack Painter"
wrote: Hi Gary, the difference that is relevant, I believe, is a waveguide for microwave broadcast through the inside space of the guide, and there is minmal current intentionally allowed on the waveguide. As I did explain, skin effect must be avoided in microwave and it is due to the frequencies, however it may be exploited in HF conductors which can eliminate wasted center-core weight and cost. This is because of the drastically different behavior of microwave from HF. And velocities inside a waveguide are much faster than HF on a conductor. The attenuator you are describing allows skin effect (it cannot avoid it either) but the true waveguide avoids it, with the microwave reflecting off the walls of the guide. Hams can use a tubing-shield to fox hunt in a building, but it is a stretch of the phrase to call hiding a hh in the tube a wave guide beyond cutoff. Please check your premises. There is no standard depth for any frequency, rather it varies drastically from one ohmic value of a given material (conductor) to another. Jack, what velocities are you talking about that are different at microwaves? The frequency has nothing to do with how fast energy propagates in a transmission line or anywhere else, regardless of what you may think you read somewhere. Electron movement may slow as frequency increases because of the magnetic forces developed in the conductor but that does not slow the energy transfer. It only forces the electrons to flow closer to the surface of the conductor. (skin effect) The electrons deeper in the conductor are stopped from moving by the counter magnetic fields developed in the conductor. That is what you are reading about that is moving slower. The only reason I even mention wave guides here is that I mentioned "WAVE GUIDE BEYOND CUTOFF" that is the proper electrical term to describe why RF does not flow on the inside of a copper tube even if the end of the tube is open and connected to the outside of the tube. When the frequency is too low for the diameter of the tube to function as a wave guide then it is said to be acting as a wave guide that is beyond the cutoff frequency. Meaning RF will not propagate through it. And propagation in the wave guide mode is the ONLY way that current will flow on the inside of a copper tube. Coax cable must have a center conductor in it in order for current to flow on the inside of a coax cable. Otherwise it will perform just like the copper tube. By the way there are very high currents that flow on the inside walls of a wave guide. That is why they are usually silver plated inside. It is a transmission line. Jack, I don't know what you have been reading in regards to skin effect but it is very real and present. Any time the frequency is above DC it is present. In some cases at low frequencies it can be ignored because it is insignificant but at radio frequencies it does come into play. And also as I mentioned in power transmission it is a factor to be considered even though the frequency is only 60 hz. In home wiring it is not a factor to be concerned with as the conductors are too small but in large transmission lines it is of concern. At HF frequencies skin effect is enough that the RF does not penetrate even the thinnest cable shield of a coax cable. Even typical "hard line" coax has a thinner shield than typical copper pipe that you are saying "conducts clear through". Why do you think then that there can be no RF energy on the outside of a coax cable?? I don't know what you mean "there is no standard depth for any frequency"? It is well known. At 60 hz the skin depth is around 1/3 of an inch. Very significant in a power transmission cable. Or a lightning ground cable.. Look up any large power cable ratings and you will usually find a DC resistance specified and an AC resistance also specified. The AC resistance is due to skin effect. Here are some figures on skin depth for copper: Skin depth (in mils) = 2.602/(sq. root of frequency in Mhz). At 1.8 Mhz it's 1.94 mils or ..00194 inches, just under 2 thousandths. It decreases as the inverse square root of frequency so at twice the frequency it will be .707 times as deep, and half as deep at 4 times the frequency. At 29.7 Mhz it's about half a thousandth. At 4 or 5 skin depths any additional thickness ceases to have additional value. Now how can you argue with that! :) Regards Gary |
SSB Antenna connection
"Gary Schafer" wrote
Jack, I don't know what you have been reading in regards to skin effect but it is very real and present. Hi Gary, when a poster asked for the formulas for this discussion, I could not display them in the newsgroup (ascii) so I pasted several of them on a website..... http://members.cox.net/pc-usa/station/skineffect.htm I don't know what you mean "there is no standard depth for any frequency"? It is well known. The resistance of a particular conductor, not just it's material, must be known to calculate skin depth. Averaging it with constants will produce the wide variety of depths that are seen in different formulas and tables. At 60 hz the skin depth is around 1/3 of an inch. Very significant in a power transmission cable. Or a lightning ground cable.. Look up any large power cable ratings and you will usually find a DC resistance specified and an AC resistance also specified. The AC resistance is due to skin effect. Yes I agreed with you it is relevant only at very high power or long lengths when inductive reactance becomes as important as DC resistance. Here are some figures on skin depth for copper: Skin depth (in mils) = 2.602/(sq. root of frequency in Mhz). At 1.8 Mhz it's 1.94 mils or .00194 inches, just under 2 thousandths. It decreases as the inverse square root of frequency so at twice the frequency it will be .707 times as deep, and half as deep at 4 times the frequency. At 29.7 Mhz it's about half a thousandth. At 4 or 5 skin depths any additional thickness ceases to have additional value. Gary, the problem with using those constants is, again, it will allow you to reduce the skin depth to nearly nothing, when in fact below a certain cross section at HF frequencies, formula predictions for skin depth cease to be relevant. The current, assumed to be constant, cannot continue to use less and less cross section until it has nothing to work with. The formulas are an approximation that allows designers to consider the resistance casued by skin effect and use an appropriately sized conductor. For instance, I could not use 1,000w on thin RG-8X if your application from a table using constants was accurate. At 5 mhz there is considerable cross section of that small diameter center conductor carrying current. That is why the center conductors are not paper-thin hollow tubes the way the outer shield _can_ be. Do you agree? Best, Jack |
SSB Antenna connection
On Wed, 9 Jun 2004 13:40:29 -0400, "Jack Painter" wrote: "Gary Schafer" wrote Jack, I don't know what you have been reading in regards to skin effect but it is very real and present. Hi Gary, when a poster asked for the formulas for this discussion, I could not display them in the newsgroup (ascii) so I pasted several of them on a website..... http://members.cox.net/pc-usa/station/skineffect.htm I don't know what you mean "there is no standard depth for any frequency"? It is well known. The resistance of a particular conductor, not just it's material, must be known to calculate skin depth. Averaging it with constants will produce the wide variety of depths that are seen in different formulas and tables. Yes it depends on the shape too. A round conductor will be slightly different than a flat conductor but for our purposes it is in the ball park. The constant comes from actual calculations. The constant makes it easier than going through all the math to obtain the constant. At 60 hz the skin depth is around 1/3 of an inch. Very significant in a power transmission cable. Or a lightning ground cable.. Look up any large power cable ratings and you will usually find a DC resistance specified and an AC resistance also specified. The AC resistance is due to skin effect. Yes I agreed with you it is relevant only at very high power or long lengths when inductive reactance becomes as important as DC resistance. The AC resistance that I am referring to has nothing to do with any reactance due to cable length. Reactance is of course another factor that enters into the picture but AC resistance in this case is referring to that resistance caused by skin effect. Not reactance. Here are some figures on skin depth for copper: Skin depth (in mils) = 2.602/(sq. root of frequency in Mhz). At 1.8 Mhz it's 1.94 mils or .00194 inches, just under 2 thousandths. It decreases as the inverse square root of frequency so at twice the frequency it will be .707 times as deep, and half as deep at 4 times the frequency. At 29.7 Mhz it's about half a thousandth. At 4 or 5 skin depths any additional thickness ceases to have additional value. Gary, the problem with using those constants is, again, it will allow you to reduce the skin depth to nearly nothing, when in fact below a certain cross section at HF frequencies, formula predictions for skin depth cease to be relevant. The current, assumed to be constant, cannot continue to use less and less cross section until it has nothing to work with. The formulas are an approximation that allows designers to consider the resistance casued by skin effect and use an appropriately sized conductor. For instance, I could not use 1,000w on thin RG-8X if your application from a table using constants was accurate. At 5 mhz there is considerable cross section of that small diameter center conductor carrying current. That is why the center conductors are not paper-thin hollow tubes the way the outer shield _can_ be. Do you agree? RG-8X will get a little warm with 1000 watts on it. The main reason the center conductors are not paper thin hollow tubes is because of physical restraints. If your argument would hold up then none of the hard line coax would have hollow tubing for their center conductors. Some of it is used in extremely high power at HF as well as UHF. Only the outer surface of the center conductor is of much importance in conduction. While it is true that it gets more complicated to predict actual skin effect on a thin conductor because as said before, the current does not completely stop at a certain depth. It decreases exponentially. But usually 4 or 5 skin depths are sufficient for all practical purposes. At that depth of 4 skin depths less than 2% of the current on the surface will be present. We use .37 as a skin depth but .368 is closer to what it works out to. .368 x .368 x .368 x .368 = .183 or 1.83% But I think the original argument was whether or not the same current or any current would flow on the inside of a copper tube at HF. It goes away quickly and can't propagate inside as explained earlier. Regards Gary Best, Jack |
SSB Antenna connection
In article ,
Gary Schafer wrote: snipped because we all know this stuff.......right? Now how can you argue with that! :) Regards Gary Gary, I think that your "Beating a Dead Horse" here....Jack just isn't going to get it. Seems he can't wrap his mind around Physics 101. Very nice explanations, though....... Bruce in alaska -- add a 2 before @ |
SSB Antenna connection
On Thu, 10 Jun 2004 03:09:50 GMT, Bruce in Alaska
wrote: In article , Gary Schafer wrote: snipped because we all know this stuff.......right? Now how can you argue with that! :) Regards Gary Gary, I think that your "Beating a Dead Horse" here....Jack just isn't going to get it. Seems he can't wrap his mind around Physics 101. Very nice explanations, though....... Bruce in alaska Thanks Bruce. I do think he has the blinders tightly strapped on. Regards Gary |
SSB Antenna connection
"Jack Painter" wrote in
news:Vlxxc.5736$5B2.5631@lakeread04: Larry, we've probably had the details of this antenna system in pieces across various posts, but would you mind putting in one place here? Sounds like an intersting and well thought out setup. Thanks, Jack It isn't very fancy, actually. The Icom AT-140 tuner is screwed to the top of the aft cabin just aft of the mizzen mast, which is deck stepped. The HV RF output post is about 8" from the base of the insulated backstay on the main and a short, smoothly bent piece of #12 Copperweld antenna wire is hose clamped to the Amel's backstay jack out of the way of the winch handle socket. The insulator is about a ft from the mast at the top and every time I look up there I want an insulator on each end of the triatic stay with an interconnecting Copperweld wire connecting the top of the backstay antenna to the center of the insulated triatic to make it a capacitor hat on top of the 50' sloping vertical for the lower frequency bands. If it ever goes back into the yard for demasting, it will have it...(c; But, for now, it just has the backstay. When Geoffrey got the boat, the previous owner reported poor performance (he was a ham, too) from the backstay antenna, which I traced down to loading from the stainless cable topping lift on the large main boom, sucking off the signal to the mast because when the boom was centered, it was only a few inches from the backstay. Not good. So, we changed the stainless to nylon and now no metal gets near the antenna, no matter where the boom is set. Signal reports came up a LOT! Directly beneath the tuner, in the support for the deck stepped mast, are several storage holes I can put wires into. So, I got a #8 battery wire, black of course, and put a ring terminal to fit the ground post on the tuner on one end. As straight as I could, I routed it down through the openings in the mount into the engine compartment which is right under the mast. Directly under the tuner, too, is the DC shunt used for the ampere- hour meter on the house batteries under the shunt. This great ground, to the big 700 AH house batteries against the hull, and the whole house ground system, is tied in at the shunt, then the cable drops straight down to the engine block for more grounding and capacitive coupling through the hull. Antenna current came way up as did signal reports from this installation. Dropping a bare Copperweld wire over the side I use for even more grounding while underway at sea, I measure only about 1.5 ohms from the bare wire laying on the bottom of the marina and this ground connection above. Something's got a great connection to the ocean down there. I musta got lucky. That's it. The radio is grounded to a ground strap Amel installed behind the panel behind the chart table. It's a common ground strap where all my instrumentation, navigation and communications is tied with small wire. There is a direct connection between that strap at the nav station and the engine block and house ground, too. I like to think it may bypass some static hits, but haven't been through any on this boat....yet. Let's not rush the testing of this theory. Larry W4CSC |
SSB Antenna connection
Gary Schafer wrote in
: Sorry Jack but you are wrong. It has nothing to do with microwave frequencies. A wave guide beyond cutoff is the mode that the tube is operating in and it simply tells you that the frequency is too low for the given size tube to propagate through. The energy inside the tube gets shorted out. Many 2-30 mhz signal generators use that type attenuator. And, if a Navy sailor has used them, the 50 ohm 1/8W resistors are cooked from having transmitters keyed into the attenuators, too, negating any possibility of CALIBRATION....Been there, fixed them for years for a living...(c; Put your ohmmeter from the center pin of the output cable to the shield and see if it measures 50 ohms....quick test. It has everything to do with it. Skin effect is ever present in all conductors at ALL frequencies. Note my reference to 60 hz power transmission where it is also important. Skin effect musta been why RG-8A melted when I keyed those twin 4-1000A home brew linears I used to build into them...hee hee. I got accused of hooking them up to the AC line to blow them at my ham club meeting. No, wait, I think that was "dielectric heating" at 6KW....sorry. RG-17A/U didn't melt. That is a contradiction to your point. You say that current flows entirely through the walls of copper tubing and then say that is why it is used in AM broadcast components. If that were true then they would not use copper tubing but instead they would use solid copper rod for better conduction. The reason copper tubing is used is that there is no current of any significance past a certain depth and to use solid rod would be a waste of copper. Hogwash. They use copper tubing because it's cheap at the local air conditioner supply house and because, if the station is above 5KW, copper tubing COOLS itself better because it has a bigger radiating surface than copper wire of the same cross section. Skin effect is immeasurable at 550- 1600 Khz.....or 20 Mhz, actually. Skin effect starts rearing its head up in the VHF to UHF range where my 2 meter kilowatt used 2" copper plumbing tubes and Ts for a plate tank for the 4CX250Bs in push pull. As we eventually got around to research rather than blindly arguing positions of opinion, then the participants hopefully learned something. I've learned that applying the math from formulas for skin effect in conductors of known ohmic value and used with a known frequency can determine the wall thickness of a conductor which has full cross sectional current on it. Guess what? The original poster's question about using copper tubing remains answered. A 1" copper tube has more surface area and carries just as much low power RF on it's entire cross section as a 1" wide piece of copper strap that is nearly the same gage. Skin effect is the reason coax cable works as it does. None of the RF on the inside of the cable appears on the outside of the cable. Other than leakage between strands of the shield of the cable. Those wire strands on coax cable are pretty thin. Much thinner than your copper pipe. Hard line has no leakage. Geez, all this time I was told it worked in TEM mode, with the H field around the center conductor perpendicular to the E field from center conductor to shield, with the RF flowing up the dielectric, like RF fields will. I never heard of skin effect at, say, 20 Khz, where coax also works just fine, properly terminated of course. I'm gonna call WWVB and warn 'em! Lots of RF appears on the outside of cheap coax with chinzy braid, which is why we double shield RG-6 on cable systems and use aluminum hardline to keep the FCC from kicking our asses on the Aircraft Band near the airport. Regards Larry |
SSB Antenna connection
On Fri, 11 Jun 2004 23:03:16 -0000, Larry W4CSC wrote: Gary Schafer wrote in : Sorry Jack but you are wrong. It has nothing to do with microwave frequencies. A wave guide beyond cutoff is the mode that the tube is operating in and it simply tells you that the frequency is too low for the given size tube to propagate through. The energy inside the tube gets shorted out. Many 2-30 mhz signal generators use that type attenuator. And, if a Navy sailor has used them, the 50 ohm 1/8W resistors are cooked from having transmitters keyed into the attenuators, too, negating any possibility of CALIBRATION....Been there, fixed them for years for a living...(c; Put your ohmmeter from the center pin of the output cable to the shield and see if it measures 50 ohms....quick test. It has everything to do with it. Skin effect is ever present in all conductors at ALL frequencies. Note my reference to 60 hz power transmission where it is also important. Skin effect musta been why RG-8A melted when I keyed those twin 4-1000A home brew linears I used to build into them...hee hee. I got accused of hooking them up to the AC line to blow them at my ham club meeting. No, wait, I think that was "dielectric heating" at 6KW....sorry. RG-17A/U didn't melt. You were right the first time. Dielectric loss is not a factor below 100 mhz. Only lack of large enough conductor surface area causes heating / loss. That is a contradiction to your point. You say that current flows entirely through the walls of copper tubing and then say that is why it is used in AM broadcast components. If that were true then they would not use copper tubing but instead they would use solid copper rod for better conduction. The reason copper tubing is used is that there is no current of any significance past a certain depth and to use solid rod would be a waste of copper. Hogwash. They use copper tubing because it's cheap at the local air conditioner supply house and because, if the station is above 5KW, copper tubing COOLS itself better because it has a bigger radiating surface than copper wire of the same cross section. Skin effect is immeasurable at 550- 1600 Khz.....or 20 Mhz, actually. Skin effect starts rearing its head up in the VHF to UHF range where my 2 meter kilowatt used 2" copper plumbing tubes and Ts for a plate tank for the 4CX250Bs in push pull. Nooo ooo, not you too Larry. Did it occur to you that copper tubing with the same cross section as copper wire has much greater SURFACE AREA? That would help with cooling and also, believe it or not reduce skin effect so it didn't get as hot in the first place. Ever heard of litz wire? I am sure you have. It is often used in small coils to reduce skin effect losses. And guess what, it is most effective below frequencies of 1 mhz. So if skin effect was not a factor at those low frequencies what would be the need for litz wire? Got any old 10khz or 50 khz coils laying around? I bet you will find some litz wire in them. The old command set receivers with the 85 khz IF's are wound with litz wire. Wanna guess why. As we eventually got around to research rather than blindly arguing positions of opinion, then the participants hopefully learned something. I've learned that applying the math from formulas for skin effect in conductors of known ohmic value and used with a known frequency can determine the wall thickness of a conductor which has full cross sectional current on it. Guess what? The original poster's question about using copper tubing remains answered. A 1" copper tube has more surface area and carries just as much low power RF on it's entire cross section as a 1" wide piece of copper strap that is nearly the same gage. Skin effect is the reason coax cable works as it does. None of the RF on the inside of the cable appears on the outside of the cable. Other than leakage between strands of the shield of the cable. Those wire strands on coax cable are pretty thin. Much thinner than your copper pipe. Hard line has no leakage. Geez, all this time I was told it worked in TEM mode, with the H field around the center conductor perpendicular to the E field from center conductor to shield, with the RF flowing up the dielectric, like RF fields will. I never heard of skin effect at, say, 20 Khz, where coax also works just fine, properly terminated of course. I'm gonna call WWVB and warn 'em! Oh I am sure they already know about it! Next time you are playing with your big amp tuning your mobile antenna, try swapping out your solid wire loading coil with the same size copper tubing for a coil and see if either one gets any hotter. If skin effect doesn't exist then your solid copper coil should be much cooler of the two. Regards Gary Lots of RF appears on the outside of cheap coax with chinzy braid, which is why we double shield RG-6 on cable systems and use aluminum hardline to keep the FCC from kicking our asses on the Aircraft Band near the airport. Regards Larry |
SSB Antenna connection
"Larry W4CSC" wrote
It isn't very fancy, actually. The Icom AT-140 tuner is screwed to the top of the aft cabin just aft of the mizzen mast, which is deck stepped. The HV RF output post is about 8" from the base of the insulated backstay on the main and a short, smoothly bent piece of #12 Copperweld antenna wire is hose clamped to the Amel's backstay jack out of the way of the winch handle socket. The insulator is about a ft from the mast at the top and every time I look up there I want an insulator on each end of the triatic stay with an interconnecting Copperweld wire connecting the top of the backstay antenna to the center of the insulated triatic to make it a capacitor hat on top of the 50' sloping vertical for the lower frequency bands. If it ever goes back into the yard for demasting, it will have it...(c; But, for now, it just has the backstay. When Geoffrey got the boat, the previous owner reported poor performance (he was a ham, too) from the backstay antenna, which I traced down to loading from the stainless cable topping lift on the large main boom, sucking off the signal to the mast because when the boom was centered, it was only a few inches from the backstay. Not good. So, we changed the stainless to nylon and now no metal gets near the antenna, no matter where the boom is set. Signal reports came up a LOT! Directly beneath the tuner, in the support for the deck stepped mast, are several storage holes I can put wires into. So, I got a #8 battery wire, black of course, and put a ring terminal to fit the ground post on the tuner on one end. As straight as I could, I routed it down through the openings in the mount into the engine compartment which is right under the mast. Directly under the tuner, too, is the DC shunt used for the ampere- hour meter on the house batteries under the shunt. This great ground, to the big 700 AH house batteries against the hull, and the whole house ground system, is tied in at the shunt, then the cable drops straight down to the engine block for more grounding and capacitive coupling through the hull. Antenna current came way up as did signal reports from this installation. Dropping a bare Copperweld wire over the side I use for even more grounding while underway at sea, I measure only about 1.5 ohms from the bare wire laying on the bottom of the marina and this ground connection above. Something's got a great connection to the ocean down there. I musta got lucky. That's it. The radio is grounded to a ground strap Amel installed behind the panel behind the chart table. It's a common ground strap where all my instrumentation, navigation and communications is tied with small wire. There is a direct connection between that strap at the nav station and the engine block and house ground, too. I like to think it may bypass some static hits, but haven't been through any on this boat....yet. Let's not rush the testing of this theory. Larry W4CSC Sounds great Larry, Thanks. Seen in a Univ of Florida study, paraphrased: 1. All boats can be struck by lightning, protected or not, and 2. Protected boats and unprotected boats both suffer damage when hit, and 3. Unprotected boats suffer significantly more damage than protected boats. It sounds like you and Lionheart are well protected. I remember a night of terrible line squalls that wrecked several yachts in Block Island Salt Harbor. I had stayed up on deck with gear on as I knew it was coming as I returned from a night on the town. It was worse than any summer line squall should have been! By the time I roused my family the winds had the entire harbor dragging anchor. Anyne who has been there can imagine the panic of watching your Out Island 41 heading toward mega-million yachts both dragging along with you, and lining the docks for a busy weekend. The Westerbeke diesel with one anchor could not hold us, and I went forward to set a second anchor and lots of chain with it. I think there must have been hundreds of lightning srtikes all around us without any break between them. Night turned to day, and that helped avoid touching shrouds while on deck. Everything around us seemed to be getting hit, and of course it was one of those moments when (at least I) thought I was going to die from lightning at any moment. But the second anchor and the diesel held us just short of one of the hundred-footers at the outer docks. In the aftermath, we heard there was a lot more damage from collisions than from lightning, and that is amazing considering how many yachts I saw get struck that night. Best, Jack |
SSB Antenna connection
"Jack Painter" wrote in
news:16syc.157$Jk5.41@lakeread02: outer docks. In the aftermath, we heard there was a lot more damage from collisions than from lightning, and that is amazing considering how many yachts I saw get struck that night. I've read the webpage from FL. Very interesting research. The mast looks tall when you're standing at the bottom of it looking up, but in the overall height of a thunderstorm FIVE MILES HIGH, our masts are like a dimple on the dining room table, and not much of a "target". I was at the transmitter shack of WRJA-TV, the PBS station in Sumter, SC, visiting an old friend who was chief engineer, Bill Jones, one night. We were building the first weather radio repeater after Bill had applied for, and gotten, an FCC license for that band to simply repeat the signal from Columbia, SC's weather station to the local Sumter area which had trouble hearing it. We made it out of kit ham radio repeater boards from VHF Engineering in Binghamton, NY, as we had a local repeater. A huge thunderstorm cell moved across Sumter and actually went THROUGH the 1800' WRJA-TV tower while we watched out the back door as lightning went SIDEWAYS 10 miles in the cloud just to hit that big 1800' ground rod sticking up out of the table-flat terrain of eastern Sumter County. I'm standing there watching the light show and suddenly Bill taps me on the shoulder and hands me a big yellow rain coat, saying, "Come on. I wanna show you something neat." We followed the huge hardline coaxial cables from the 35KW TV transmitter out to the base of the antenna and Bill says, "You're standing in the safest place in Sumter County. There is a cone of protection against being hit by lightning provided by my tower and you're now standing in the middle of it. Hang onto the tower leg and feel the current going through it." I burned my hand a couple of times as the huge BOOMs went off over my head a thousand feet up. The huge bridge cables JUMPED from the surge of electrical EMP hit them, many times. The lights went out and we had to go back in the building to reset the transmitters when the power came back on. Though the "tower" on the sailboat is very short, in comparison, I like to think that if you have a proper grounding system, like the professor describes on his webpages, you are also in a tiny cone where the blast will mostly be shunted AROUND you, which is why your car is so safe in a thunderstorm. The current surge that kills goes AROUND the the steel body of the car....Steel ships and boats do that....Plastic, not so good. Larry |
SSB Antenna connection
(sigh)
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