Re: Topband: Radials on ground v FCP
On 1/10/2022 1:13 PM, Jim Brown wrote: As usual, I agree with Rick. But I'd like to observe that an extensive study of loaded mobile whips published in two parts in QEX about ten years ago showed that inductive loading, especially at the base, was a 73, Jim K9YC I wasn't clear. I assumed that the vertical has top loading wires, and the base loading inductor is added to get resonance. According to W8JI, once you have enough top loading to get uniform current in the vertical, then it is OK to have a base mounted tuning inductor. For short verticals, making the top wires extremely long to achieve resonance without a loading coil is sub optimal because it reduces the radiation resistance too much. I once resonated a 60 foot vertical on 160 meters using two 100 foot top umbrella wires, because it was a temporary antenna and I didn't want to fool with a loading coil. The drive impedance was very low. 73 Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
According to Roy Lewallens Eznec site there are no more expensive versions of his Eznec software. He is retiring and is leaving a last version for free download. Take a look at Eznec.com for details. Lee K7TJR OR -Original Message- From: Topband On Behalf Of Jim Brown Sent: Monday, January 10, 2022 1:13 PM To: topband@contesting.com Subject: Re: Topband: Radials on ground v FCP As usual, I agree with Rick. But I'd like to observe that an extensive study of loaded mobile whips published in two parts in QEX about ten years ago showed that inductive loading, especially at the base, was a bad idea, and that the closer loading moved to the top, the more efficient was the radiated field. The published work included extensive measurements of various positions of the loading, with top loading being the best. Which is what we're doing with both the L and the T. One fly in the ointment in our understanding is that most modeling software, especially if it models inductive loading as a lumped element, fails to correctly model the phase of current through the inductor. Some years ago, W7EL added a method of modeling inductors using his EZNEC interface as a large number of small inductors in a spiral geometry, in an attempt to correct for this. Thus a practical inductor could include hundreds of (or even a thousand) elements, so it requires one of the more expensive versions of his software, and takes a while to crank. 73, Jim K9YC On 1/10/2022 11:24 AM, Richard (Rick) Karlquist wrote: > Actually, you are kidding yourself making the inverted L long enough > to be resonant. That has the effect of moving more current into the > horizontal part of the inverted L, which is also not desirable. The > solution to this dilemma is to use a top loaded (T type) vertical, and > a loading coil if necessary. The resonant inverted L is "elegant" but > not optimal. _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
As usual, I agree with Rick. But I'd like to observe that an extensive study of loaded mobile whips published in two parts in QEX about ten years ago showed that inductive loading, especially at the base, was a bad idea, and that the closer loading moved to the top, the more efficient was the radiated field. The published work included extensive measurements of various positions of the loading, with top loading being the best. Which is what we're doing with both the L and the T. One fly in the ointment in our understanding is that most modeling software, especially if it models inductive loading as a lumped element, fails to correctly model the phase of current through the inductor. Some years ago, W7EL added a method of modeling inductors using his EZNEC interface as a large number of small inductors in a spiral geometry, in an attempt to correct for this. Thus a practical inductor could include hundreds of (or even a thousand) elements, so it requires one of the more expensive versions of his software, and takes a while to crank. 73, Jim K9YC On 1/10/2022 11:24 AM, Richard (Rick) Karlquist wrote: Actually, you are kidding yourself making the inverted L long enough to be resonant. That has the effect of moving more current into the horizontal part of the inverted L, which is also not desirable. The solution to this dilemma is to use a top loaded (T type) vertical, and a loading coil if necessary. The resonant inverted L is "elegant" but not optimal. _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
On 1/10/2022 10:42 AM, Kenny Silverman wrote: N6BT’s ring is pretty flexible in its dimensions. It can be 3 or 4 sides (or anywhere in between) and can handle some variation in symmetry. I’ve been having issues finding a solution to the high tree attenuation on my property and I had an inverted L with the ring and another inverted L 340’ away with 60 x 100’ radials. The model showed there was some interaction between the 2 antennas so exact difference was not known. But basically the ring was very close to the 60 radial version. One of the key issues is making sure the inverted L section is close to resonance. If it’s short, more current is moved into the ring which is not desirable. Regards , Kenny K2KW _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector Actually, you are kidding yourself making the inverted L long enough to be resonant. That has the effect of moving more current into the horizontal part of the inverted L, which is also not desirable. The solution to this dilemma is to use a top loaded (T type) vertical, and a loading coil if necessary. The resonant inverted L is "elegant" but not optimal. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
N6BT’s ring is pretty flexible in its dimensions. It can be 3 or 4 sides (or anywhere in between) and can handle some variation in symmetry. I’ve been having issues finding a solution to the high tree attenuation on my property and I had an inverted L with the ring and another inverted L 340’ away with 60 x 100’ radials. The model showed there was some interaction between the 2 antennas so exact difference was not known. But basically the ring was very close to the 60 radial version. One of the key issues is making sure the inverted L section is close to resonance. If it’s short, more current is moved into the ring which is not desirable. Regards , Kenny K2KW _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
I took my inspiration for the one turn counterpoise idea from HF Antenna For All Locations page 155, Fig 11.9(m). David G3UNA > On 09 January 2022 at 17:09 CUTTER DAVID via Topband > wrote: > > > Thanks, Rick. > > My particular circumstances limit me to a small triangle of ground in the > corner of a field and the FCP suits that very well. It would be interesting > to know how the FCP compares to something well known, like a broadcast > station ground. > > I like the idea of the spiral counterpoise: I experimented with a one turn > counterpoise in EZNEC > at 3 m above ground level. It looked workable but too big for my space, so, > I could make that into a spiral and perhaps not be too concerned about > symmetry. However, looking to Guy's idea of stacking the wires vertically so > they shade the ground underneath might be worth a try. Compressing things > always seems to limit bandwidth, so, that's something to be wary of. > > David G3UNA > > > > On 09 January 2022 at 16:22 "Richard (Rick) Karlquist" > > wrote: > > > > > > > > On 1/9/2022 4:51 AM, CUTTER DAVID via Topband wrote: > > > Hi Rob > > > > > > I see copper prices have doubled in the last year. > > > > > > My intention is to compare and contrast the cost and performance of short > > > verticals over a large field of ground radials v the very modest amount > > > of wire required for the FCP. In Guy's article > > > > > > > This is a false dichotomy between FCP and a broadcast station ground > > screen. The best use of wire is to have a small number of elevated > > tuned radials with proper RF choking. As shown by N6LF, you can do well > > with just 8 radials, about 100 feet long each. On 160 meters, they > > should be 20 feet high for optimum performance. BTW, cheap aluminum > > electric fence wire works perfectly for elevated radials Also consider > > N6BT's single spiral radial configuration as an alternative to FCP. > > > > Rick N6RK > _ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
On 1/9/2022 8:22 AM, Richard (Rick) Karlquist wrote: electric fence wire works perfectly for elevated radials Also consider N6BT's single spiral radial configuration as an alternative to FCP. Rick N6RK _ See: https://nextgenerationantennas.com/presentations-1 Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
Thanks, Rick. My particular circumstances limit me to a small triangle of ground in the corner of a field and the FCP suits that very well. It would be interesting to know how the FCP compares to something well known, like a broadcast station ground. I like the idea of the spiral counterpoise: I experimented with a one turn counterpoise in EZNEC at 3 m above ground level. It looked workable but too big for my space, so, I could make that into a spiral and perhaps not be too concerned about symmetry. However, looking to Guy's idea of stacking the wires vertically so they shade the ground underneath might be worth a try. Compressing things always seems to limit bandwidth, so, that's something to be wary of. David G3UNA > On 09 January 2022 at 16:22 "Richard (Rick) Karlquist" > wrote: > > > > On 1/9/2022 4:51 AM, CUTTER DAVID via Topband wrote: > > Hi Rob > > > > I see copper prices have doubled in the last year. > > > > My intention is to compare and contrast the cost and performance of short > > verticals over a large field of ground radials v the very modest amount of > > wire required for the FCP. In Guy's article > > > > This is a false dichotomy between FCP and a broadcast station ground > screen. The best use of wire is to have a small number of elevated > tuned radials with proper RF choking. As shown by N6LF, you can do well > with just 8 radials, about 100 feet long each. On 160 meters, they > should be 20 feet high for optimum performance. BTW, cheap aluminum > electric fence wire works perfectly for elevated radials Also consider > N6BT's single spiral radial configuration as an alternative to FCP. > > Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
On 1/9/2022 4:51 AM, CUTTER DAVID via Topband wrote: Hi Rob I see copper prices have doubled in the last year. My intention is to compare and contrast the cost and performance of short verticals over a large field of ground radials v the very modest amount of wire required for the FCP. In Guy's article This is a false dichotomy between FCP and a broadcast station ground screen. The best use of wire is to have a small number of elevated tuned radials with proper RF choking. As shown by N6LF, you can do well with just 8 radials, about 100 feet long each. On 160 meters, they should be 20 feet high for optimum performance. BTW, cheap aluminum electric fence wire works perfectly for elevated radials Also consider N6BT's single spiral radial configuration as an alternative to FCP. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
Hi Rob I see copper prices have doubled in the last year. My intention is to compare and contrast the cost and performance of short verticals over a large field of ground radials v the very modest amount of wire required for the FCP. In Guy's article https://k2av.com/Olinger_NCJ_article_on_FCP.pdf he says "The reason for the FCP is twofold: minimal space and a low-loss alternative to radials." I would add that it is also lower cost, to your point. I interpret his analysis as saying that the layout of the FCP minimises its own ground loss so well that only the radiator's ground loss is left to compare to the "gold standard" of 120 ground radials. I hope someone will jump in and correct me if I've misinterpreted that. If not, would it be correct to say that the FCP method of loss reduction differs only by 1.7 dB (from Guy's article) compared to the "gold standard" of 120 ground radials? I don't have that Griffith book, so, would you summarise the difference between 120 ground radials and the fewer radials proposed when using <1/4 w vertical? I'd like to get a feel for how it compares to the FCP method. 73 David G3UNA > On 08 January 2022 at 18:14 Rob Atkinson wrote: > > > I can't comment on the folded counterpoise because I am not familiar > with it. The "broadcast model" which I take to mean 120 radials is > used because in the case of a 90 degree tower on medium wave, the > earth current intensity is far enough from the feed point to > necessitate a higher number of radials so that as they diverge, they > are not so far apart from each other that the earth losses are > unacceptable. Few hams have 1/4 w. towers for 160 m., and instead > employ shorter vertical radiators such as inverted Ls* and Ts, (1/8 w. > for example) so the ground current intensity is high much closer to > the feedpoint. This means that fewer radials can be used because they > are shorter and at their ends, are still an acceptable separation from > each other. Of course, ground conductivity plays a part also. This > is good news for hams who want to save money on expensive wire. All > of this is detailed in the Griffith book I referenced previously. > > 73 > Rob > K5UJ > > *Unlike the T, the horizontal portion of the inverted L radiates. > W1BB recommended extending radials that run along underneath it if > possible, and I think that was good advice. > > On Sat, Jan 8, 2022 at 9:27 AM CUTTER DAVID wrote: > > > > Rob > > > > I recall a discussion on here some years ago which proposed that, whilst > > being an amazing antenna for top band, if you could achieve it, the > > broadcast model was not necessarily the best use of resources for amateur > > purposes, on the basis that broadcasters are mainly interested in ground > > wave to cover a defined relatively short range service area, whereas > > amateurs a more interested in dx. > > > > I don't recall how that discussion ended, but for purposes of saving wire, > > at least, the K2AV folded counterpoise (FCP) must be about as good as > > anyone could attain. How it performs against that broadcast model would be > > of interest. > > > > David G3UNA > _ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
Hi Frank, It was definitely Cleveland. Got my abbreviations wrong after 60 years. :) Thanks, Jim On 1/8/2022 12:10 PM, Frank W3LPL wrote: Hi Jim, Didn't Carl Smith run CIE (Cleveland Institute of Electronics) and not CREI (Capitol Radio Engineering Institute)? 73 Frank W3LPL - Original Message - From: "K9YC" To: "topband" Sent: Saturday, January 8, 2022 5:36:03 PM Subject: Re: Topband: Radials on ground v FCP On 1/8/2022 7:27 AM, CUTTER DAVID via Topband wrote: I recall a discussion on here some years ago which proposed that, whilst being an amazing antenna for top band, if you could achieve it, the broadcast model was not necessarily the best use of resources for amateur purposes, on the basis that broadcasters are mainly interested in ground wave to cover a defined relatively short range service area, whereas amateurs a more interested in dx. The function of radial systems under a vertical radiator is solely to minimize loss in the very near field. That has nothing to do with the means of propagation -- i.e., ground wave vs skywave. With directional arrays of verticals, widely used it broadcasting as well as ham radio, they have a second function, directly related to the first, of controlling the nulls in the pattern by minimizing differences the contribution of each element by making those losses as small as possible. Radial systems in broadcasting are (or at least were) controlled because licenses were granted on the basis of carefully controlled coverage areas, and for protection of other stations on the same or adjacent channels. I learned about this as an EE student, working in the consulting office of Pete Johnson, whose practice was designing these arrays to fit new stations into the AM band that had been full for 20 years. Pete and Carl Smith (who ran CREI) wrote FCC AM technical Rules after WWII. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
On 1/8/2022 8:27 AM, CUTTER DAVID via Topband wrote: Rob I recall a discussion on here some years ago which proposed that, whilst being an amazing antenna for top band, if you could achieve it, the broadcast model was not necessarily the best use of resources for amateur purposes, on the basis that broadcasters are mainly interested in ground wave to cover a defined relatively short range service area, whereas amateurs a more interested in dx. Without arguing the "best use of resources" issue, work on the ground screen that improves ground wave will also improve sky wave (DX) I don't recall how that discussion ended, but for purposes of saving wire, at least, the K2AV folded counterpoise (FCP) must be about as good as anyone could attain. How it performs against that broadcast model would be of interest. David G3UNA Maybe it saves wire, but IMHO, it's a terrible ground screen. To see what I mean by "ground screen" I quote a post to this reflector by my friend Eric, N7CL, from a long time ago. Wes N7WS Quote: To: Subject: TopBand: Elevated GP vs. Vertical Antennas From: n...@mmsi.com (Eric Gustafson Courtesy Account) Date: Fri, 13 Mar 1998 17:14:28 -0700 I apologize for this but I'm not directly responding to the post of yours referred to in the header of this message. I Just grabbed it to respond to because it was a convenient way to get the subject references correct. I don't believe that the quoted insert from Tom is taken from that message. >In a message dated 98-03-08 19:05:39 EST, W8JI writes: > >> The 160 meter skin depth (distance where current drops to 37% >> of the value traveling in the conductor) is about 30 meters in >> poor soil, ten meters in good soil, and about a foot in salt >> water. Current effectively goes to zero at about 10 skin >> depths. > > The above is a very interesting statement. Let me see if I can make use of it to illuminate _why_ the full ground screen (either on or in the ground surface) provides a system with less loss than a system of six or fewer elevated radials. First, I'd like to separate the discussion to a strict comparison of one ground system versus the other when used to provide the ground system for (nearly at least) identical vertical radiators. Please note that I'm NOT saying that elevated radials don't work, or that they don't work well enough to make a useful antenna. Only that when used near the earth's surface, they cannot provide the same high level of efficiency as the canonical full size sufficiently dense ground screen under the same radiator. We are talking about ground mounted (less than 1/8 wave above grade) vertical radiators which are less than or equal to 1/4 wave long. The quantity of DX that can be worked with tuned rain gutters is irrelevant to this discussion. The only thing we are talking about is how many dB stronger (or weaker) is the same radiator with ground system (A) versus the same antenna with ground system (B). Frequently it is possible to work DX effectively even on topband with an antenna that is 25 dB weaker than a full size, full effeciency vertical. This is because the fade margin for the big antenna is 50 or 60 dB and -25 dB doesn't take the link SNR below zero. Here we are talking about two systems which are within 4 to 6 dB of each other. OK Now, from Tom's statement above it is pretty clear that unless some means is taken to prevent the antenna's near field zone from "seeing" the earth under the antenna, a large volume of earth will be involved in the near field interaction. The poorer the earth conductivity is, the larger the volume will be that is involved. As the apparent surface conductivity of the earth's surface increases (or is artificially increased with radials), the volume of lossy earth exposed to the near fields decreases. Eventually a point is reached where further surface conductivity increases do not produce lower losses because the dominant loss mechanism for the antenna system is no longer the near field interaction loss with the earth material. The effect of increasing the surface conductivity has been to prevent the fields from penetrating into the earth material under the antenna. Hence the name "ground screen". The ground system when sufficiently dense has "screened" or shielded the earth material from the antenna's near fields. Sufficiently dense means that the greatest distance between conductors in the screen is 0.015 wavelengths or less. For 1/4 wavelength radials, this requirement is met with 104 radials. Now, as a practical matter, relaxing the criteria to 0.03 wavelengths for a radial system results in only about a 0.5 dB reduction in measured field strength. So 60 radials this long would produce a system which is very nearly as good as one meeting the full density criteria. For radials only 1/8 wavelength long, the requirement is met with only 52 radials (26 if you are willing to give up 0.5 dB). Note that these numbers are very
Re: Topband: Radials on ground v FCP
I can't comment on the folded counterpoise because I am not familiar with it. The "broadcast model" which I take to mean 120 radials is used because in the case of a 90 degree tower on medium wave, the earth current intensity is far enough from the feed point to necessitate a higher number of radials so that as they diverge, they are not so far apart from each other that the earth losses are unacceptable. Few hams have 1/4 w. towers for 160 m., and instead employ shorter vertical radiators such as inverted Ls* and Ts, (1/8 w. for example) so the ground current intensity is high much closer to the feedpoint. This means that fewer radials can be used because they are shorter and at their ends, are still an acceptable separation from each other. Of course, ground conductivity plays a part also. This is good news for hams who want to save money on expensive wire. All of this is detailed in the Griffith book I referenced previously. 73 Rob K5UJ *Unlike the T, the horizontal portion of the inverted L radiates. W1BB recommended extending radials that run along underneath it if possible, and I think that was good advice. On Sat, Jan 8, 2022 at 9:27 AM CUTTER DAVID wrote: > > Rob > > I recall a discussion on here some years ago which proposed that, whilst > being an amazing antenna for top band, if you could achieve it, the broadcast > model was not necessarily the best use of resources for amateur purposes, on > the basis that broadcasters are mainly interested in ground wave to cover a > defined relatively short range service area, whereas amateurs a more > interested in dx. > > I don't recall how that discussion ended, but for purposes of saving wire, at > least, the K2AV folded counterpoise (FCP) must be about as good as anyone > could attain. How it performs against that broadcast model would be of > interest. > > David G3UNA _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
On 1/8/2022 7:27 AM, CUTTER DAVID via Topband wrote: I recall a discussion on here some years ago which proposed that, whilst being an amazing antenna for top band, if you could achieve it, the broadcast model was not necessarily the best use of resources for amateur purposes, on the basis that broadcasters are mainly interested in ground wave to cover a defined relatively short range service area, whereas amateurs a more interested in dx. The function of radial systems under a vertical radiator is solely to minimize loss in the very near field. That has nothing to do with the means of propagation -- i.e., ground wave vs skywave. With directional arrays of verticals, widely used it broadcasting as well as ham radio, they have a second function, directly related to the first, of controlling the nulls in the pattern by minimizing differences the contribution of each element by making those losses as small as possible. Radial systems in broadcasting are (or at least were) controlled because licenses were granted on the basis of carefully controlled coverage areas, and for protection of other stations on the same or adjacent channels. I learned about this as an EE student, working in the consulting office of Pete Johnson, whose practice was designing these arrays to fit new stations into the AM band that had been full for 20 years. Pete and Carl Smith (who ran CREI) wrote FCC AM technical Rules after WWII. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Radials on ground v FCP
Rob I recall a discussion on here some years ago which proposed that, whilst being an amazing antenna for top band, if you could achieve it, the broadcast model was not necessarily the best use of resources for amateur purposes, on the basis that broadcasters are mainly interested in ground wave to cover a defined relatively short range service area, whereas amateurs a more interested in dx. I don't recall how that discussion ended, but for purposes of saving wire, at least, the K2AV folded counterpoise (FCP) must be about as good as anyone could attain. How it performs against that broadcast model would be of interest. David G3UNA > On 08 January 2022 at 14:02 Rob Atkinson wrote: > > > For medium wave, every ham who transmits with a base excited vertical > radiator should get a copy of _Radio-Electronic Transmission > Fundamentals_ by B. Whitfield Griffith, Jr. 2nd ed., Noble Pub. Co., > Atlanta Ga., c2000, ISBN 1884932134. 638 p. Griffith is a retired > principal engineer with Continental. This classic college broadcast > engineer textbook explains many fundamentals involving medium wave > transmission in an easy to understand way. Getting the most out of > your valuable copper wire is more important now than ever because > copper has risen to insanely high prices. > > The book is probably out of print but might be available used from ABE > Books https://www.abebooks.com/ > > 73 > Rob > K5UJ > _ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
