|
Fuel tanks and SSB counterpoise.
In the process of laying up the hull I incorporated a couple hundred sq.
ft of bronze bug screen to serve as a counterpoise. In addition two runs of 2" copper foil run down the center of the hull to the keel area. Capacitors between the foil and the keel bolts isolate any DC from getting back into the counterpoise. That is probably enough but as I am installing two aluminum tanks, I wonder how kosher it would be to tie them into the counterpoise with more capacitors. It would add another 14 sq ft of coupling area but would it be introducing other problems? -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
Fuel tanks and SSB counterpoise.
Glenn Ashmore wrote in message news:JRxob.119973$sp2.25191@lakeread04...
In the process of laying up the hull I incorporated a couple hundred sq. ft of bronze bug screen to serve as a counterpoise. In addition two runs of 2" copper foil run down the center of the hull to the keel area. Capacitors between the foil and the keel bolts isolate any DC from getting back into the counterpoise. That is probably enough but as I am installing two aluminum tanks, I wonder how kosher it would be to tie them into the counterpoise with more capacitors. It would add another 14 sq ft of coupling area but would it be introducing other problems? Glenn, I think you are overdoing it....I just have a copper strap from the ground of the antenna tuner to one keel bolt (external lead keel) and when I tested the syste,after installation (in New York), I got a 55 report from a ham in NW Spain. The only time Herb (Southbound II) did not hear me loud and clear was because my copper strrap had become corroded/ john N2ZOA/MM |
Fuel tanks and SSB counterpoise.
I concur. I have internal ballast, so I drilled in and tapped in a bronze
bolt to attach the foil. I had no problems on the most recent Marion to Bermuda Race. -- Dennis Gibbons S/V Dark Lady CN35-207 email: dennis dash gibbons at worldnet dot att dot net "john s." wrote in message om... Glenn Ashmore wrote in message news:JRxob.119973$sp2.25191@lakeread04... In the process of laying up the hull I incorporated a couple hundred sq. ft of bronze bug screen to serve as a counterpoise. In addition two runs of 2" copper foil run down the center of the hull to the keel area. Capacitors between the foil and the keel bolts isolate any DC from getting back into the counterpoise. That is probably enough but as I am installing two aluminum tanks, I wonder how kosher it would be to tie them into the counterpoise with more capacitors. It would add another 14 sq ft of coupling area but would it be introducing other problems? Glenn, I think you are overdoing it....I just have a copper strap from the ground of the antenna tuner to one keel bolt (external lead keel) and when I tested the syste,after installation (in New York), I got a 55 report from a ham in NW Spain. The only time Herb (Southbound II) did not hear me loud and clear was because my copper strrap had become corroded/ john N2ZOA/MM |
Fuel tanks and SSB counterpoise.
Okay, here's another question on antenna configuration. I have just gone
through the pricing out of backstay insulators, and received the suggestion that a good, less expensive alternative would be to substitute a Kevlar backstay for the rod that I have presently, and wind a piece bare of wire around the Kevlar, up to near the masthead as an antenna. It is significantly less expensive, and the Kevlar has the advantage of being stronger and lighter than the wire. Anyone know of any disadvantages to this approach?? "john s." wrote in message om... Glenn Ashmore wrote in message news:JRxob.119973$sp2.25191@lakeread04... In the process of laying up the hull I incorporated a couple hundred sq. ft of bronze bug screen to serve as a counterpoise. In addition two runs of 2" copper foil run down the center of the hull to the keel area. Capacitors between the foil and the keel bolts isolate any DC from getting back into the counterpoise. That is probably enough but as I am installing two aluminum tanks, I wonder how kosher it would be to tie them into the counterpoise with more capacitors. It would add another 14 sq ft of coupling area but would it be introducing other problems? Glenn, I think you are overdoing it....I just have a copper strap from the ground of the antenna tuner to one keel bolt (external lead keel) and when I tested the syste,after installation (in New York), I got a 55 report from a ham in NW Spain. The only time Herb (Southbound II) did not hear me loud and clear was because my copper strrap had become corroded/ john N2ZOA/MM |
Fuel tanks and SSB counterpoise.
This doesn't address your antenna question specifically, but I have to say
that the idea of replacing a stainless wire backstay with rope just creeps me out. Sure Kevlar, in the appropriate size, could be stronger and still lighter than the wire, but its long-term durability raises some significant questions. The lifetime of stainless steel 1x19 and rod is well understood, as is the response to shock loading; I doubt that the same could be said for Kevlar. Your backstay's a pretty important rigging component - I wouldn't be inclined to screw around with it. You might also consider the long-term cost of more frequent replacement of the Kevlar, versus the cost of the wire and insulators for about a twenty-year lifetime expectancy of the SS wire and insulator combination. I'm not against Kevlar in standing rigging per se, although I'd be inclined to use it in a "supporting role", so to speak. In fact, I'm thinking of replacing my 7x19 SS wire running backstays on my 41' 3/4-rigged sloop with Kevlar the next time I re-rig, not so much to save weight as to keep down the chafing on my spreaders when the running backstays are housed at the after shrouds. I just wouldn't use in in a single-point-of-failure application such as the backstay. Tom Dacon "maxlynn" wrote in message news:hDVob.49689$hp5.39655@fed1read04... Okay, here's another question on antenna configuration. I have just gone through the pricing out of backstay insulators, and received the suggestion that a good, less expensive alternative would be to substitute a Kevlar backstay for the rod that I have presently, and wind a piece bare of wire around the Kevlar, up to near the masthead as an antenna. It is significantly less expensive, and the Kevlar has the advantage of being stronger and lighter than the wire. Anyone know of any disadvantages to this approach?? "john s." wrote in message om... Glenn Ashmore wrote in message news:JRxob.119973$sp2.25191@lakeread04... In the process of laying up the hull I incorporated a couple hundred sq. ft of bronze bug screen to serve as a counterpoise. In addition two runs of 2" copper foil run down the center of the hull to the keel area. Capacitors between the foil and the keel bolts isolate any DC from getting back into the counterpoise. That is probably enough but as I am installing two aluminum tanks, I wonder how kosher it would be to tie them into the counterpoise with more capacitors. It would add another 14 sq ft of coupling area but would it be introducing other problems? Glenn, I think you are overdoing it....I just have a copper strap from the ground of the antenna tuner to one keel bolt (external lead keel) and when I tested the syste,after installation (in New York), I got a 55 report from a ham in NW Spain. The only time Herb (Southbound II) did not hear me loud and clear was because my copper strrap had become corroded/ john N2ZOA/MM |
Fuel tanks and SSB counterpoise.
Composite stays are the big thing with multihull sailors but when I
checked it out for monohulls it seems that stretch will be a problem. High tech line seems to be strong enough but it evidently still stretches more than stainless wire. Tom Dacon wrote: This doesn't address your antenna question specifically, but I have to say that the idea of replacing a stainless wire backstay with rope just creeps me out. Sure Kevlar, in the appropriate size, could be stronger and still lighter than the wire, but its long-term durability raises some significant questions. The lifetime of stainless steel 1x19 and rod is well understood, as is the response to shock loading; I doubt that the same could be said for Kevlar. Your backstay's a pretty important rigging component - I wouldn't be inclined to screw around with it. You might also consider the long-term cost of more frequent replacement of the Kevlar, versus the cost of the wire and insulators for about a twenty-year lifetime expectancy of the SS wire and insulator combination. I'm not against Kevlar in standing rigging per se, although I'd be inclined to use it in a "supporting role", so to speak. In fact, I'm thinking of replacing my 7x19 SS wire running backstays on my 41' 3/4-rigged sloop with Kevlar the next time I re-rig, not so much to save weight as to keep down the chafing on my spreaders when the running backstays are housed at the after shrouds. I just wouldn't use in in a single-point-of-failure application such as the backstay. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
Fuel tanks and SSB counterpoise.
Okay, now that you have given your opinion on Kevlar as a backstay, how
about addressing the original question - i.e., is there any conceptual problem with wrapping a bare copper wire around it and using it for an antenna? Has anyone done this? And, oh by the way, how would you feel about using Kevlar as a substitute for 1x19 in steering cables? Would it shock you to know that many boats are using Kevlar in this highly critical application? And have been doing it successfully for over ten years now? Use as a backstay is pretty mundane by comparison. And others have been using it for a similar period as backstay material. And contrary to what you suggest, the lifetime and other properties of Kevlar are well understood. "Tom Dacon" wrote in message ... This doesn't address your antenna question specifically, but I have to say that the idea of replacing a stainless wire backstay with rope just creeps me out. Sure Kevlar, in the appropriate size, could be stronger and still lighter than the wire, but its long-term durability raises some significant questions. The lifetime of stainless steel 1x19 and rod is well understood, as is the response to shock loading; I doubt that the same could be said for Kevlar. Your backstay's a pretty important rigging component - I wouldn't be inclined to screw around with it. You might also consider the long-term cost of more frequent replacement of the Kevlar, versus the cost of the wire and insulators for about a twenty-year lifetime expectancy of the SS wire and insulator combination. I'm not against Kevlar in standing rigging per se, although I'd be inclined to use it in a "supporting role", so to speak. In fact, I'm thinking of replacing my 7x19 SS wire running backstays on my 41' 3/4-rigged sloop with Kevlar the next time I re-rig, not so much to save weight as to keep down the chafing on my spreaders when the running backstays are housed at the after shrouds. I just wouldn't use in in a single-point-of-failure application such as the backstay. Tom Dacon "maxlynn" wrote in message news:hDVob.49689$hp5.39655@fed1read04... Okay, here's another question on antenna configuration. I have just gone through the pricing out of backstay insulators, and received the suggestion that a good, less expensive alternative would be to substitute a Kevlar backstay for the rod that I have presently, and wind a piece bare of wire around the Kevlar, up to near the masthead as an antenna. It is significantly less expensive, and the Kevlar has the advantage of being stronger and lighter than the wire. Anyone know of any disadvantages to this approach?? "john s." wrote in message om... Glenn Ashmore wrote in message news:JRxob.119973$sp2.25191@lakeread04... In the process of laying up the hull I incorporated a couple hundred sq. ft of bronze bug screen to serve as a counterpoise. In addition two runs of 2" copper foil run down the center of the hull to the keel area. Capacitors between the foil and the keel bolts isolate any DC from getting back into the counterpoise. That is probably enough but as I am installing two aluminum tanks, I wonder how kosher it would be to tie them into the counterpoise with more capacitors. It would add another 14 sq ft of coupling area but would it be introducing other problems? Glenn, I think you are overdoing it....I just have a copper strap from the ground of the antenna tuner to one keel bolt (external lead keel) and when I tested the syste,after installation (in New York), I got a 55 report from a ham in NW Spain. The only time Herb (Southbound II) did not hear me loud and clear was because my copper strrap had become corroded/ john N2ZOA/MM |
Fuel tanks and SSB counterpoise.
More elegant would be to use a single braid Vectran. It would take some
patience but you could feed the wire up through the core. I still see several potential problems. The first is the termination. Arimids and other high tech lines like PBO require equal tension on all fibers to maintain rated strength. Small eye splices will cut strength considerably. Special terminations that pot the fibers inside a hollow steel fitting are available but cost more than an insulator and must be factory installed. The second is stretch. No matter how high the modulus of the fiber, braided line will creep. The Kevlar 49 stays on boats like the Volvo Ocean 70's is parallel fiber inside a polyethylene cover. A backstay cost as much as a pretty decent crosscut mainsail. BTW, composite steering cables are rarely Kevlar. With the exception of Technora, arimid fibers have a tendency to chafe against each other when the line is routinely flexed under tension as around steering sheaves. Vectran and Technora are the preferred fibers for that application. maxlynn wrote: Okay, now that you have given your opinion on Kevlar as a backstay, how about addressing the original question - i.e., is there any conceptual problem with wrapping a bare copper wire around it and using it for an antenna? Has anyone done this? And, oh by the way, how would you feel about using Kevlar as a substitute for 1x19 in steering cables? Would it shock you to know that many boats are using Kevlar in this highly critical application? And have been doing it successfully for over ten years now? Use as a backstay is pretty mundane by comparison. And others have been using it for a similar period as backstay material. And contrary to what you suggest, the lifetime and other properties of Kevlar are well understood. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
Fuel tanks and SSB counterpoise.
"maxlynn" wrote in message news:Ygppb.52870$hp5.43787@fed1read04... Okay, now that you have given your opinion on Kevlar as a backstay, how about addressing the original question - i.e., is there any conceptual problem with wrapping a bare copper wire around it and using it for an antenna? Has anyone done this? The original question (Glenn's), has to do with extending the SSB foil lattice to the fuel tanks. In response to that, the consensus of the sources I've referenced for my SSB ground system is that running the foil to the tops of the tanks is a good thing to do. I've done this on my tanks, and merely laid the foil on top of the tank surface with an adhesive bonding agent (it was probably Sikaflex). I don't believe there's any need for an electrical bond, since induction should do the job nicely. Tom Dacon |
Fuel tanks and SSB counterpoise.
In article ,
"Tom Dacon" wrote: I don't believe there's any need for an electrical bond, since induction should do the job nicely. The above doesn't take into account that we are dealing with impedance in the frequency domain. By not having an good electrial bond, you induce capacative coupling to additional surface area for your RF Ground, That means that this coupling is frequency sensative, and then the RF Grounding System will react significantly different depending on the frequency being transmitted. Autotune Antenna Couples have very specific tuning firmware, and this code doesn't react very well to a highly variable Rg Ground impedance. They are designed to operate against a FLAT RF Ground Impedance, and the more bumps in the RF Gropund impedance the harder the tuner has to work to tune the antenna, and the more phantom, and quirky Low SWR points that the tuner will find, and lock on to. Bruce in alaska -- add a 2 before @ |
Fuel tanks and SSB counterpoise.
When I could not tune out the ground impedance bumps, I installed a cheap
manual antenna tuner in the ground circuit leg. Then I got perfect impedance matches at all frequencies into a long ground wire. This was in addition to the normal automatic antenna tuner for the antenna. Tuning was simple. Just adjust the ground tuner until the SWR was down to the lowest you could get. Larry DeMers Bruce in Alaska wrote: In article , "Tom Dacon" wrote: I don't believe there's any need for an electrical bond, since induction should do the job nicely. The above doesn't take into account that we are dealing with impedance in the frequency domain. By not having an good electrial bond, you induce capacative coupling to additional surface area for your RF Ground, That means that this coupling is frequency sensative, and then the RF Grounding System will react significantly different depending on the frequency being transmitted. Autotune Antenna Couples have very specific tuning firmware, and this code doesn't react very well to a highly variable Rg Ground impedance. They are designed to operate against a FLAT RF Ground Impedance, and the more bumps in the RF Gropund impedance the harder the tuner has to work to tune the antenna, and the more phantom, and quirky Low SWR points that the tuner will find, and lock on to. Bruce in alaska -- add a 2 before @ |
Fuel tanks and SSB counterpoise.
Bare copper will corrode rather quickly. Insulated copper would be
better but the insulation will probably degrade in the UV. Bare SS would probably be best. I have a split backstay where the split is fairly high up. I ran a separate antenna from the masthead using thin SS wire, small insulator at the top. Bottom had a small insulator and a spring to absorb any mast pumping. Attached it to the radar arch. It worked well, but not any better than the 23' fiberglass whip mounted to the transome. Doug "maxlynn" wrote in message news:Ygppb.52870$hp5.43787@fed1read04... Okay, now that you have given your opinion on Kevlar as a backstay, how about addressing the original question - i.e., is there any conceptual problem with wrapping a bare copper wire around it and using it for an antenna? Has anyone done this? And, oh by the way, how would you feel about using Kevlar as a substitute for 1x19 in steering cables? Would it shock you to know that many boats are using Kevlar in this highly critical application? And have been doing it successfully for over ten years now? Use as a backstay is pretty mundane by comparison. And others have been using it for a similar period as backstay material. And contrary to what you suggest, the lifetime and other properties of Kevlar are well understood. "Tom Dacon" wrote in message ... This doesn't address your antenna question specifically, but I have to say that the idea of replacing a stainless wire backstay with rope just creeps me out. Sure Kevlar, in the appropriate size, could be stronger and still lighter than the wire, but its long-term durability raises some significant questions. The lifetime of stainless steel 1x19 and rod is well understood, as is the response to shock loading; I doubt that the same could be said for Kevlar. Your backstay's a pretty important rigging component - I wouldn' t be inclined to screw around with it. You might also consider the long-term cost of more frequent replacement of the Kevlar, versus the cost of the wire and insulators for about a twenty-year lifetime expectancy of the SS wire and insulator combination. I'm not against Kevlar in standing rigging per se, although I'd be inclined to use it in a "supporting role", so to speak. In fact, I'm thinking of replacing my 7x19 SS wire running backstays on my 41' 3/4-rigged sloop with Kevlar the next time I re-rig, not so much to save weight as to keep down the chafing on my spreaders when the running backstays are housed at the after shrouds. I just wouldn't use in in a single-point-of-failure application such as the backstay. Tom Dacon "maxlynn" wrote in message news:hDVob.49689$hp5.39655@fed1read04... Okay, here's another question on antenna configuration. I have just gone through the pricing out of backstay insulators, and received the suggestion that a good, less expensive alternative would be to substitute a Kevlar backstay for the rod that I have presently, and wind a piece bare of wire around the Kevlar, up to near the masthead as an antenna. It is significantly less expensive, and the Kevlar has the advantage of being stronger and lighter than the wire. Anyone know of any disadvantages to this approach?? "john s." wrote in message om... Glenn Ashmore wrote in message news:JRxob.119973$sp2.25191@lakeread04... In the process of laying up the hull I incorporated a couple hundred sq. ft of bronze bug screen to serve as a counterpoise. In addition two runs of 2" copper foil run down the center of the hull to the keel area. Capacitors between the foil and the keel bolts isolate any DC from getting back into the counterpoise. That is probably enough but as I am installing two aluminum tanks, I wonder how kosher it would be to tie them into the counterpoise with more capacitors. It would add another 14 sq ft of coupling area but would it be introducing other problems? Glenn, I think you are overdoing it....I just have a copper strap from the ground of the antenna tuner to one keel bolt (external lead keel) and when I tested the syste,after installation (in New York), I got a 55 report from a ham in NW Spain. The only time Herb (Southbound II) did not hear me loud and clear was because my copper strrap had become corroded/ john N2ZOA/MM |
Fuel tanks and SSB counterpoise.
In article ,
"Doug Dotson" wrote: It worked well, but not any better than the 23' fiberglass whip mounted to the transome. At what frequency? All Frequencies? A 23' fiberglass whip is a VERY short antenna at 2182Khz, and m ost autotuners will not even get a tuned Indication with such an antenna system. Bruce in alaska -- add a 2 before @ |
Fuel tanks and SSB counterpoise.
In article , Larry Demers
wrote: When I could not tune out the ground impedance bumps, I installed a cheap manual antenna tuner in the ground circuit leg. Then I got perfect impedance matches at all frequencies into a long ground wire. This was in addition to the normal automatic antenna tuner for the antenna. Tuning was simple. Just adjust the ground tuner until the SWR was down to the lowest you could get. Larry DeMers If your going to use a manual tuner in the ground system, and have to readjust it for every large frequency change, why would you not just put the manual tuner on the antenna and just do manual tuning??? Kind of redudndent isn't it. The whole point of a autotuner is so that the operator doen't have to know or understand what the tuner is doing. That, and so appliance operators could install their own SSB Radio's systems and cut the Marine Electronics Tech's out of their Installation Money. Same thing, as when the FCC changed the rules for Radar Installations, by users, only with many more consequencies. Bruce in alaska -- add a 2 before @ |
Fuel tanks and SSB counterpoise.
Since no one answered your question,,
Yes it would be a problem winding a wire around the line. That is if you make very many turns of the wire. It will act like a choke to the RF and only the very bottom part of the "coil" of wire will be effective as an antenna. The rest of it will be electrically disconnected as far as the RF is concerned due to the inductance of the choke that you have made. This is of course at the higher frequencies. It may work fairly well at 2182. The old AM whip antennas that were used on 2 and sometimes on 4 mhz and not on higher frequencies had a center loading coil wound on them. This increased their efficiency over just a straight whip and putting all the loading coil in the antenna tuner. With the coil higher up on the antenna it provided a little higher feed point impedance and resulted in a more efficient antenna. This worked well when only 2 and 4 mhz was involved. But when higher frequencies are fed to such an antenna that loading coil that worked wonders on the low frequencies acts like a choke at the higher frequencies and effectively disconnects everything above the coil, including part or most of the coil. You then have only a very short antenna working for you making it very inefficient. You could fasten a straight piece of wire to the kevlar and it should work fine. Regards Gary On Sat, 1 Nov 2003 13:32:36 -0800, "maxlynn" wrote: Okay, here's another question on antenna configuration. I have just gone through the pricing out of backstay insulators, and received the suggestion that a good, less expensive alternative would be to substitute a Kevlar backstay for the rod that I have presently, and wind a piece bare of wire around the Kevlar, up to near the masthead as an antenna. It is significantly less expensive, and the Kevlar has the advantage of being stronger and lighter than the wire. Anyone know of any disadvantages to this approach?? "john s." wrote in message . com... Glenn Ashmore wrote in message news:JRxob.119973$sp2.25191@lakeread04... In the process of laying up the hull I incorporated a couple hundred sq. ft of bronze bug screen to serve as a counterpoise. In addition two runs of 2" copper foil run down the center of the hull to the keel area. Capacitors between the foil and the keel bolts isolate any DC from getting back into the counterpoise. That is probably enough but as I am installing two aluminum tanks, I wonder how kosher it would be to tie them into the counterpoise with more capacitors. It would add another 14 sq ft of coupling area but would it be introducing other problems? Glenn, I think you are overdoing it....I just have a copper strap from the ground of the antenna tuner to one keel bolt (external lead keel) and when I tested the syste,after installation (in New York), I got a 55 report from a ham in NW Spain. The only time Herb (Southbound II) did not hear me loud and clear was because my copper strrap had become corroded/ john N2ZOA/MM |
Fuel tanks and SSB counterpoise.
The coil in the center of an antenna is not a choke it is just an
inductor that electrically lengthens the antenna. This method is used well above 2-4 mhz in mobile radio. It is not used much above VHF because a full wave length is already relatively small. Ron |
Fuel tanks and SSB counterpoise.
The coil in the center of a marine antenna that is designed to be used
on 2 mhz is indeed a choke at anything above 7 mhz or so. It is not intended to be such but that is what it is when the antenna is used above its intended range. All of the antenna above the coil is electrically disconnected from the lower part of the antenna. You could physically remove that upper portion and notice little if any difference at higher frequencies. That is the reason that type of antenna is not used on any system that operates above 4 mhz. A straight whip (no coil involved) is the only thing that will work satisfactorily in a multi band system. (trap antenna being the exception) Those old antennas with the loading coil in them perform much better on 2 mhz than the straight whip antenna of the same physical length but they are very poor on the higher bands as part of the antenna is not there electrically. It is then a very short antenna at the higher frequencies. Regards Gary On Thu, 20 Nov 2003 21:37:05 -0500 (EST), (Ron Thornton) wrote: The coil in the center of an antenna is not a choke it is just an inductor that electrically lengthens the antenna. This method is used well above 2-4 mhz in mobile radio. It is not used much above VHF because a full wave length is already relatively small. Ron |
Fuel tanks and SSB counterpoise.
Well I guess if I tried to push 30 mhz thru a 2 mhz transmitter you
could call the transmitter a choke too. But in reality it ain't and the coil in the middle of an antenna ain't either. What you describe as a choke is a tuning inductor, the choking is an inconsequential behavior of the tuning at a frequency the antenna was never designed to operate at. Ron |
Fuel tanks and SSB counterpoise.
If it acts like a choke it must be a choke. :)
Regards Gary On Fri, 21 Nov 2003 09:52:46 -0500 (EST), (Ron Thornton) wrote: Well I guess if I tried to push 30 mhz thru a 2 mhz transmitter you could call the transmitter a choke too. But in reality it ain't and the coil in the middle of an antenna ain't either. What you describe as a choke is a tuning inductor, the choking is an inconsequential behavior of the tuning at a frequency the antenna was never designed to operate at. Ron |
Fuel tanks and SSB counterpoise.
In article ,
Gary Schafer wrote: The coil in the center of a marine antenna that is designed to be used on 2 mhz is indeed a choke at anything above 7 mhz or so. It is not intended to be such but that is what it is when the antenna is used above its intended range. All of the antenna above the coil is electrically disconnected from the lower part of the antenna. You could physically remove that upper portion and notice little if any difference at higher frequencies. That is the reason that type of antenna is not used on any system that operates above 4 mhz. A straight whip (no coil involved) is the only thing that will work satisfactorily in a multi band system. (trap antenna being the exception) Those old antennas with the loading coil in them perform much better on 2 mhz than the straight whip antenna of the same physical length but they are very poor on the higher bands as part of the antenna is not there electrically. It is then a very short antenna at the higher frequencies. Regards Gary On Thu, 20 Nov 2003 21:37:05 -0500 (EST), (Ron Thornton) wrote: The coil in the center of an antenna is not a choke it is just an inductor that electrically lengthens the antenna. This method is used well above 2-4 mhz in mobile radio. It is not used much above VHF because a full wave length is already relatively small. Ron Just a few comments here on this thread....... Gary is right on in his assesment of the operation of the end feed loaded antenna. The coil does indeed act as a choke on frequencies higher than 4XResonant. In the "Old Days" we used Morad 2800 and 3600 loaded whips with 15 to 35 ft of wire below them as antennas in the MF Frequency Range. They were just great below 5 Mhz, and not half bad above that as the coil only choked off the upper 102" whip and the coil itself, and left the bottom 10ft of antenna and 35 Ft of wire as an antenna for the HF Ranges above 5 Mhz. This 45 Ft of antenna did just fine as an antenna in those ranges as it would be tuned (Fixed tuned antenna tuner era) as 3/4 Wavelength at these higher frequencies. today's autotuners have a similar tuning firmware routine that adds output Capacitance untill it finds the 3/4 Wavelength point. They don't do as good of job as a Fixed tuned tuner due to the step size and the sense circuits, but they will get close, and be fairly effecent. The trick to make this type of antenna work is to get some wire under the antenna, so that you have an effective antenna length once the coil chokes off, as the frequency rises. Most of the North Pacific Fishing Fleet uses this type of antenna system for MF, and HF, comms. Bruce in alaska -- add a 2 before @ |
Fuel tanks and SSB counterpoise.
|
Fuel tanks and SSB counterpoise.
Wires with a big coil in the middle is what I'm talking about. I guess
this is a semantics thing. I can't get used to calling it a choke cause in fixed station if we wanted to change freq that much we went out and threw up another 3 curtain full wave Rhombic. You mobile guys are strange, you want one antenna to do it all. Ron |
Fuel tanks and SSB counterpoise.
Just can't figure out how to get a Rhombic on a sailboat. We don't expect
one antenna to do it all. I have separate antennas for HF, VHF, TV, GPS, WX SAT, DGPS, FM, HAM VHF, HAM UHF. If only a single antenna could do it all. Doug, k3qt s/v Callista "Ron Thornton" wrote in message ... Wires with a big coil in the middle is what I'm talking about. I guess this is a semantics thing. I can't get used to calling it a choke cause in fixed station if we wanted to change freq that much we went out and threw up another 3 curtain full wave Rhombic. You mobile guys are strange, you want one antenna to do it all. Ron |
Fuel tanks and SSB counterpoise.
|
Fuel tanks and SSB counterpoise.
I have five on my 26 foot sail boat. Marine VHF on the stern, Amateur on
the port spreader, TV on the starboard spreader, A scanner and a GPS on the mast head. One Ground in a square foot of copper clad on the keel. (Salt water sailor only) "Bruce in Alaska" wrote (Ron Thornton) wrote: Wires with a big coil in the middle is what I'm talking about. I guess this is a semantics thing. I can't get used to calling it a choke cause in fixed station if we wanted to change freq that much we went out and threw up another 3 curtain full wave Rhombic. You mobile guys are strange, you want one antenna to do it all. Ron Ron, on a vessel, you ostly only have room for one antenna..... |
Fuel tanks and SSB counterpoise.
"Roger Gt" wrote in message . com... I have five on my 26 foot sail boat. Marine VHF on the stern, Amateur on the port spreader, TV on the starboard spreader, A scanner and a GPS on the mast head. One Ground in a square foot of copper clad on the keel. (Salt water sailor only) "Bruce in Alaska" wrote (Ron Thornton) wrote: Wires with a big coil in the middle is what I'm talking about. I guess this is a semantics thing. I can't get used to calling it a choke cause in fixed station if we wanted to change freq that much we went out and threw up another 3 curtain full wave Rhombic. You mobile guys are strange, you want one antenna to do it all. Ron Ron, on a vessel, you ostly only have room for one antenna..... |
Fuel tanks and SSB counterpoise.
"Roger Gt" wrote in message . com... I have five on my 26 foot sail boat. Marine VHF on the stern, Amateur on the port spreader, TV on the starboard spreader, A scanner and a GPS on the mast head. Why would one mount a gps antenna on the masthead? Wouldn't the normal roll of the boat cause that antenna to travel several feet and cause the position to change on each cycle? I would think rail or arch mounted would be more stable. Ours is mounted in the overhead of the pilot house in the opening for the sliding hatch, which is lexan. Leanne S/V Fundy |
Fuel tanks and SSB counterpoise.
Sorry I miss-spoke.
GPS on the cabin roof. Scanner on the Mast head. "Leanne" wrote in message ... "Roger Gt" wrote in message . com... I have five on my 26 foot sail boat. Marine VHF on the stern, Amateur on the port spreader, TV on the starboard spreader, A scanner and a GPS on the mast head. Why would one mount a gps antenna on the masthead? Wouldn't the normal roll of the boat cause that antenna to travel several feet and cause the position to change on each cycle? I would think rail or arch mounted would be more stable. Ours is mounted in the overhead of the pilot house in the opening for the sliding hatch, which is lexan. Leanne S/V Fundy |
Fuel tanks and SSB counterpoise.
Roger Gt wrote:
One Ground in a square foot of copper clad on the keel. (Salt water sailor only) I guess the big steel/iron ballast keel (couple of thousand pounds AIUI) on bottom of my Westerly would make a 'good' RF ground? Connect to SS keel bolt/s accessible in bilge. Taking other precautions for elctrolysis and/or 'ground' currents from shore power? Terry. |
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