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: K9AY Loop Questions
Thank you Jose, Here's an earlier Ref.. R. Keen; Wireless Direction Finding and Directional Reception 1927 Page 75. Describes Heart-Shape Circuit (Societe Francaise Radio Electrique) using a two turn loop with a connexion to ground via a variable resistor. It is very much like the K9AY. A two turn K9AY with the a 1m separation at the horizontal ends of the triangle or diamond shape with give approx. 3dB gain increase providing that the loops total length doesn't exceed approx. Lambda/4. Great for MW and LF work. Size for size this antenna has the highest gain of all the terminate cardioid loops. J. A. Lambert G3FNZ RadCom Nov. 82 Describes the C & S Antennas Ltd Directional active loop receiving antenna system. The article describes how cardioid pattern is created from the loops figure of 8 pattern ( H field ) and the monpole mode ( E field ). 73 Andrew Hi Andrew In this case it is very important to consider that both antennas are close to the ground. It means the reflection from the ground is different for vertical vectors, that see a image below the ground in the same phase and the horizontal vector that see a 180 degree image that cancel the horizontal components in opposite phase. The vertical components adds because they are in phase. There are very few books about loaded loop receiver antennas, most because the WWII use. https://wwrof.org/webinar-archive/high-performance-rx-antennas-for-a-small-lot/ See the slides download. You will find a reference of the first loaded loop patent. 1938 Horizontal polarized. Harold Beverage patents 1938 1941 ( 80 years ago) •US 2138134 A Phasing antennas •US 2247743 A Broad Band RX Antenna • https://patentimages.storage.googleapis.com/73/83/00/14943032331cef/US2247743.pdf and 1940 vertical polarized 1940. Nearly all the newly re-invented compact receive antennas derive from the terminated loop, the earliest reference was in an appallingly mimeographed prewar training manual of W3EEE Dad‘s 1973 COMMUNICATIONS 74 CONFERENCE BRIGHTON Wednesday, June 5 1974 — Session 5 Equipment Design Paper 5.3: Loop Antennas for HF Reception Contributed by: B.S.Collins, C & S Antennas Ltd., 73’s JC N4IS _ 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
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: K9YC's comments on radials
I can only echo Jim's comments about mechanical issues with very thin wire. I use aluminum fence wire #17 guage, and have to coil/uncoil my radials for the mowing season. This wire works fine but tends to kink - and breaks fairly easily when uncoiling. Once Ive used up my supply, I'll be going back to jacketed stranded copper wire. Its much easier to use. For those who lay down aluminum radials of #17 or thinner, and leave it on the surface of the ground, there probably wouldnt be much of an issue. Im not so sure about buried aluminum of the lighter guages due to corrosion. My surface aluminum radials are now 5-7 years old and holding up fine other than the kinking/breaking issue. I take it nice and easy when coiling/uncoiling. - ** _ 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
Re: Topband: Radials on ground
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
