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Rhombics
On Sun, 1 Oct 2006 17:50:47 -0500, "Richard Fry"
wrote: no form of NEC and its Windows shells will show in a _single_ evaluation whether in tabular or graphical form, the net values of the surfacewave+spacewave elevation pattern at a user-specified distance over real earth, for all elevation angles in a given azimuth slice? I'm surprised that Roy didn't take credit for this where credit is due. The near-field table (which complete conforms to your constraints) can be expressed in a spherical coordinate system. I've used this feature often. 73's Richard Clark, KB7QHC |
Rhombics
Alan Peake wrote in
: Before I go to the trouble of putting up a rhombic, I've been using NEC to get an idea of the gain, radiation angle etc for various leg lengths. It all looks very promising on the computer but I'd be interested in real-world experiences. For example, how well does the real antenna approach the PC simulation when various factors like wire sag, uneven ground, presence of trees and shrubbery? I only ever had the use of one REAL rhombic. And that was on 60m in the high arctic (gov't freqs). It was properly designed for the specific path we were using and yes, it was VERY good. You could almost make your own band opening with 5kw! Properly designed, they have a good reputation for doing what the theory says they will do. Just remember, though, that you're going to have to sewer almost half your transmitted power into the terminating resistor. But that's the half that would be going the wrong way, basically. -- Dave Oldridge+ ICQ 1800667 |
Rhombics
"Roy Lewallen" wrote in message ... Antenna modeling tools aren't intended to model propagation effects. But the stronger the signal radiated in the right direction, the stronger the received signal will be. And the strength of the radiated signal in each direction is what the antenna modeling program shows. True, not argument there. As for the "effect of capture area", the "capture area" of an antenna is just another way of stating the gain. This information is what you get from an antenna modeling program. Roy Lewallen, W7EL What I had in mind is the difference in "capture area" related to physical size of antenna like rhombic vs. similar gain, say Yagi. It appears that rhombics perform better than corresponding Yagi thanks to larger physical size (5 - 10 wave lengths) interacting with the environment (more like diversity effect?). It seems that rhombics perform better than calculated gain/capture area figures. We will have opportunity to do some tests of rhombics farm vs. some classics soon. It will be interesting to see the results. 73 Yuri |
Rhombics
Yuri Blanarovich wrote:
What I had in mind is the difference in "capture area" related to physical size of antenna like rhombic vs. similar gain, say Yagi. It appears that rhombics perform better than corresponding Yagi thanks to larger physical size (5 - 10 wave lengths) interacting with the environment (more like diversity effect?). That's a commonly believed myth, but myth it is. It seems that rhombics perform better than calculated gain/capture area figures. So do EH, CFA, Isotron, Rai-beam, and more other antennas that I can count. That's because modeling programs just don't account for the magical effects. We will have opportunity to do some tests of rhombics farm vs. some classics soon. It will be interesting to see the results. Maybe. Even fairly simple RF measurements are very difficult to make with even modest accuracy. Antenna measurements are more difficult yet. Roy Lewallen, W7EL |
Rhombics
On Sun, 01 Oct 2006 20:27:47 -0700, Roy Lewallen
wrote: So do EH, CFA, Isotron, Rai-beam, and more other antennas that I can count. That's because modeling programs just don't account for the magical effects. To add to the list, secret / undescribed / proprietary components that impart the "special" features. Owen -- |
Rhombics
"Richard Clark" wrote:
I've been modeling for results at the horizon for as long as I've held a copy of EL/EZNEC. This and the Brown, Lewis, Epstein data confirm to within 1dB as I've reported on more than one occasion. _____________ Even the demo version of EZNEC, used judiciously, can do that. The link below leads to a screen clip of EZNEC output windows. EZNEC parameters were set for the 1937 BL&E study for a 90 degree monopole, and the r-f ground produced by ~113 radials each about 0.41 lambda long EZNEC shows an h-plane field of 189.76 mV/m at 1 mile for 1 kw of applied power. The BL&E paper shows about 191 mVm for those conditions (Figure 30). The EZNEC calculation for these conditions differs from the BL&E paper by less than 0.06 dB. http://i62.photobucket.com/albums/h8...EC-2Emulat.gif RF PS: And many thanks to Roy Lewallen for making a demo version of EZNEC available. |
Rhombics
"Roy Lewallen" wrote in message ... Yuri Blanarovich wrote: What I had in mind is the difference in "capture area" related to physical size of antenna like rhombic vs. similar gain, say Yagi. It appears that rhombics perform better than corresponding Yagi thanks to larger physical size (5 - 10 wave lengths) interacting with the environment (more like diversity effect?). That's a commonly believed myth, but myth it is. Perhaps "myth" based on actual experiences. W6AM had a rhombic farm and results in contests and comparison with locals using competitive antennas seem to give it edge over calculations. I had rhombic once also and experienced exceptional reports. I know it is anecdotal "evidence" but those who used it, know the difference. Professional installations used them and I have not seen them replacing it with the "same gain" Yagis. It seems that rhombics perform better than calculated gain/capture area figures. So do EH, CFA, Isotron, Rai-beam, and more other antennas that I can count. That's because modeling programs just don't account for the magical effects. I would not put rhombics in the same category, that is a stretch. We saw the "infallability" of modeling programs using lumped inductors as loading elements. We will have opportunity to do some tests of rhombics farm vs. some classics soon. It will be interesting to see the results. Maybe. Even fairly simple RF measurements are very difficult to make with even modest accuracy. Antenna measurements are more difficult yet. Roy Lewallen, W7EL Very simple RF measurement is when comparing two antennas, one hearing the signals, while another one is not. One example at VE1ZZ: he has few beverages for Eu. Regular one, phased pair, staggered pair and the "weird" one terminated on a stainless steel hubcap in the salt water, very similar to the Regular one. The SS beats all the others most of the time. They are about the same length ~870 ft, can the modeling figure out wasaaap? I am just trying to find excuse for seemingly superb performance of rhombics, attributing it perhaps to diversity effect by being stretched over large area. I am not selling any, but have access to about 30 of them over salt water marsh and will play with them. 73 Yuri, K3BU |
Rhombics
Dave Oldridge wrote: Properly designed, they have a good reputation for doing what the theory says they will do. Just remember, though, that you're going to have to sewer almost half your transmitted power into the terminating resistor. But that's the half that would be going the wrong way, basically. But it would get there - eventually :) Long or short path. But I don't know if both paths are ever open at the same time to the same extent. If not, then it may not be a problem. What about running a transmission line from where the terminating R would be, back to the feed point? Assuming you can match it all that is. Alan |
Rhombics
Alan Peake wrote:
Dave Oldridge wrote: Properly designed, they have a good reputation for doing what the theory says they will do. Just remember, though, that you're going to have to sewer almost half your transmitted power into the terminating resistor. But that's the half that would be going the wrong way, basically. But it would get there - eventually :) Long or short path. But I don't know if both paths are ever open at the same time to the same extent. If not, then it may not be a problem. What about running a transmission line from where the terminating R would be, back to the feed point? Assuming you can match it all that is. No problem. Pipe the signal back from the far end into the shack, feed it into a circulator, and add it to the outgoing signal. Cecil will explain what happens to the power :-) Replying to Yuri's point: from personal experience of using a rhombic 100 wavelengths long for 2m moonbounce, it had only about the same maximum gain as a box of 4 mid-size yagis - and that is only while the moon is passing through the very narrow main beam, which only happens for a magic 20 minutes on certain days of the month. In other words, the rhombic did work, but the performance was nowhere near as spectacular as we had expected from its huge electrical length. What is undeniably true is that it *looked* spectacular! I've used many kinds of antennas since then, up to an 85ft dish, but not one of them has given me the same buzz as that rhombic. And there is the trap: buzz isn't the same thing as performance. We need to be very careful about applying dual standards. An unavoidable feature of all very long rhombics is that the main beam is very narrow, because the edges of the main lobe are sliced away by large numbers of sidelobes that are not many dB down. If we saw that kind of E-plane pattern in a yagi, we wouldn't hesitate to call it a "bad design"... so what's "good" about the same feature in a rhombic? -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek |
Rhombics
Ian White GM3SEK wrote:
Pipe the signal back from the far end into the shack, feed it into a circulator, and add it to the outgoing signal. Cecil will explain what happens to the power :-) Dr. Best, VE9SRB, in his 2001 QEX articles explained what would happen. Based on his idea that 75w + 8.33w = 133.33w, one could route the unused Rhombic power back to the source, recycle it, and cause voltage superposition to multiply the power up to a factor of 4. :-) To anyone who thinks I am kidding about Dr. Best posting the above equation, it can probably be verified by Google circa May 2001 on this newsgroup. Dr. Best proved his assertions with the following power equation: Ptot = P1 + P2 + 2[SQRT(P1*P2)]cos(A) where A is the angle between V1 and V2. If we make the angle between V1 and V2 equal to zero, we can take the P1 power from the source and the P2 power routed back from the load and increase our total power output by a factor equal to 2[SQRT(P1*P2)]. Who says there is no such thing as a free lunch? :-) Discussed by me in May 2001 was the fact that his term, 2[SQRT(P1*P2)] is constructive interference energy which must necessarily be exactly balanced by 2[SQRT(P1*P2)] watts of destructive interference energy or else the conservation of energy principle is violated. At the time, Dr. Best did not understand where the necessary destructive interference energy was coming from. It comes from the Z0-match between the feedline and the source and it works exactly like the thin-film layer on non-reflective glass. Dr. Best's Ptot equation above is true for A = 0 if and only if Ptot is being supplied with destructive interference energy where A is probably equal to 180 degrees. -- 73, Cecil http://www.w5dxp.com |
Rhombics
Howdy Rhombic fans,
OK on Ian's rhombic experiences on V/UHF, but that I believe would be different situation, I.e. rhombic not working in conjunction with ground reflections/effects. With "normal" HF rhombic we have a situation where antenna is spread out over few wavelengths and interacting with ground. Spacing two antennas few wavelengths can give us diversity effect by the virtue of propagation and waves hitting them differently. Rhombic is kind of antenna/feeders spread out over few wavelengths over ground. Perhaps there is also some of traveling wave mode going on, like in a Beverage. You can't simulate that or use VHF analogy being many wavelength away from the ground effects. Don't forget that skywave polarization is all over and rolling around. I see big differences when trying to model vertical arrays destined to work on ground and modeled in "free space", different pattern and just plain ridiculous to do that. I know from my hardware experiments with Razors (quad - yagi) that if I changed height of the boom and I reoptimized the spacing/dimensions I would get different configuration. So my conclusion was that antenna has to be designed for the height it is going to be used at. Closer to ground, the more pronounced effect. What I am trying to say and not sell anything, is that perhaps the ground effect and rhombic's spread over it over few wavelengths might have something to do with it's good performance. I think that software modeling is a great tool, but I also know that it can not capture all the variables and effects that are happening around antennas, the ground and the sky. All I am pointing out that based on mine and other's experience, rhombic is a great antenna, performing perhaps better than modeling shows (W8JI web site downplays it). If I get the chance, I will try to do some real life tests and comparisons on HF. We have some 30 rhombics, some phased side by side and will try to model and compare them with other antennas. BTW our rhombics have a load resistor made of open (resistive?) wire stub, folded few times back and forth. They were used with 50 kW transmitters. see http://www.teslaradio.org/site_survey.htm I am just trying to bring attention to possible discrepancy that perhaps is worth exploring. If some believe in gospel of modeling and paper antennas, than enjoy it. I prefer reality. When I wrote my observations about propagation happening by ducting and refraction some 25 years ago, I was ridiculed. Now the propagation experts are accepting it and playing discoverers (only ON4UN gives me some credit :-). Yuri, K3BU Tesla RC N2EE "Ian White GM3SEK" wrote in message ... Alan Peake wrote: Dave Oldridge wrote: Properly designed, they have a good reputation for doing what the theory says they will do. Just remember, though, that you're going to have to sewer almost half your transmitted power into the terminating resistor. But that's the half that would be going the wrong way, basically. But it would get there - eventually :) Long or short path. But I don't know if both paths are ever open at the same time to the same extent. If not, then it may not be a problem. What about running a transmission line from where the terminating R would be, back to the feed point? Assuming you can match it all that is. No problem. Pipe the signal back from the far end into the shack, feed it into a circulator, and add it to the outgoing signal. Cecil will explain what happens to the power :-) Replying to Yuri's point: from personal experience of using a rhombic 100 wavelengths long for 2m moonbounce, it had only about the same maximum gain as a box of 4 mid-size yagis - and that is only while the moon is passing through the very narrow main beam, which only happens for a magic 20 minutes on certain days of the month. In other words, the rhombic did work, but the performance was nowhere near as spectacular as we had expected from its huge electrical length. What is undeniably true is that it *looked* spectacular! I've used many kinds of antennas since then, up to an 85ft dish, but not one of them has given me the same buzz as that rhombic. And there is the trap: buzz isn't the same thing as performance. We need to be very careful about applying dual standards. An unavoidable feature of all very long rhombics is that the main beam is very narrow, because the edges of the main lobe are sliced away by large numbers of sidelobes that are not many dB down. If we saw that kind of E-plane pattern in a yagi, we wouldn't hesitate to call it a "bad design"... so what's "good" about the same feature in a rhombic? 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek |
Rhombics
"Ian White GM3SEK" wrote in message ... Alan Peake wrote: Dave Oldridge wrote: Properly designed, they have a good reputation for doing what the theory says they will do. Just remember, though, that you're going to have to sewer almost half your transmitted power into the terminating resistor. But that's the half that would be going the wrong way, basically. But it would get there - eventually :) Long or short path. But I don't know if both paths are ever open at the same time to the same extent. If not, then it may not be a problem. What about running a transmission line from where the terminating R would be, back to the feed point? Assuming you can match it all that is. No problem. Pipe the signal back from the far end into the shack, feed it into a circulator, and add it to the outgoing signal. Cecil will explain what happens to the power :-) Replying to Yuri's point: from personal experience of using a rhombic 100 wavelengths long for 2m moonbounce, it had only about the same maximum gain as a box of 4 mid-size yagis - and that is only while the moon is passing through the very narrow main beam, which only happens for a magic 20 minutes on certain days of the month. In other words, the rhombic did work, but the performance was nowhere near as spectacular as we had expected from its huge electrical length. What is undeniably true is that it *looked* spectacular! I've used many kinds of antennas since then, up to an 85ft dish, but not one of them has given me the same buzz as that rhombic. And there is the trap: buzz isn't the same thing as performance. We need to be very careful about applying dual standards. An unavoidable feature of all very long rhombics is that the main beam is very narrow, because the edges of the main lobe are sliced away by large numbers of sidelobes that are not many dB down. If we saw that kind of E-plane pattern in a yagi, we wouldn't hesitate to call it a "bad design"... so what's "good" about the same feature in a rhombic? -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek |
Rhombics
Yuri Blanarovich wrote:
[snip] I am just trying to bring attention to possible discrepancy that perhaps is worth exploring. If some believe in gospel of modeling and paper antennas, than enjoy it. I prefer reality. When I wrote my observations about propagation happening by ducting and refraction some 25 years ago, I was ridiculed. Now the propagation experts are accepting it and playing discoverers (only ON4UN gives me some credit :-). Yuri, K3BU Yuri, I am a bit puzzled by your comment. Ducting and refraction received a lot of technical and mathematical study back at least to the mid-1930's. Terman's books show similar figures to those in your CQ article, and they give numerous technical references from the 1940's. You may have been ridiculed by the amateur radio community, but the pros accepted that sort of propagation explanation many decades earlier. 73, Gene W4SZ |
Rhombics
"Alan Peake" wrote in message ... Before I go to the trouble of putting up a rhombic, I've been using NEC to get an idea of the gain, radiation angle etc for various leg lengths. It all looks very promising on the computer but I'd be interested in real-world experiences. For example, how well does the real antenna approach the PC simulation when various factors like wire sag, uneven ground, presence of trees and shrubbery? Alan VK2ADB Back in the 70s a friend and I put up a rhombic antenna in a pecan orchard on 11M. If I remember correctly each leg was about 8 wl long. At first we thought we had done something wrong but then we began regularing talking with guy about 45 miles away west of Tifton Ga.that we could not talk to on his quad. Apparently the beam width is so narrow it makes it impractical except for point to point comunication. |
Rhombics
Ian, GM3SEK commented thoughtfully on many points regarding the rhombic.
It is an excellent antenna for fixed point communications. Unfortunately, the earth and moon are not stationary with respect to each other. The rhombic may not be so re-directable as antennas like the Yagi or corner reflector. For transmitting, the rhombic has a lower maximum voltage than a resonant standing-wave antenna. For high power, it`s a consideration. The power remaining at the far end of the rhombic has been recycled by some to eliminaate waste. Cecil does an excellent job of explaining where the power in a transmission line goes. Unfortunately, re-entrant rhombics tend to lose some of their advantages of simplicity and bandwidth in the elaboration process. On the subject of diversity, it works by switching to a better receiving system. Without switching, spaced antennas only provide a phased array in which destructive interference happens during some signal conditions. Where I worked, we used triple diversity receivers with 3 rhombic antennas spaced about 10 wavelengths apart at the low frequency end of the spectrum. A Crosby or Pioneer combiner selected the best of the 3 receiver outputs to feed a program line. Several receiving systems shared the same 3 rhombics for simultaneous program relay. Sidelobes are only a small problem when using triple diversity and selectable sideband in reception. Best regards, Richard Harrison, KB5WZI |
Rhombics
Jimmie D wrote:
Back in the 70s a friend and I put up a rhombic antenna in a pecan orchard on 11M. If I remember correctly each leg was about 8 wl long. Isn't that an illegal antenna on 11m? :-) -- 73, Cecil http://www.w5dxp.com |
Rhombics
Yuri Blanarovich wrote:
OK on Ian's rhombic experiences on V/UHF, but that I believe would be different situation, I.e. rhombic not working in conjunction with ground reflections/effects. With "normal" HF rhombic we have a situation where antenna is spread out over few wavelengths and interacting with ground. The same is true at VHF. All rhombics interact with ground, because their length is many times greater than their height above ground. The number of wavelengths above ground will change the details, but not the basic fact. Spacing two antennas few wavelengths can give us diversity effect by the virtue of propagation and waves hitting them differently. Rhombic is kind of antenna/feeders spread out over few wavelengths over ground. Perhaps there is also some of traveling wave mode going on, like in a Beverage. You can't simulate that Are you quite sure of that? In other words, do you have firm evidence and reasons why? or use VHF analogy being many wavelength away from the ground effects. That analogy was your assumption, never mine :-) Don't forget that skywave polarization is all over and rolling around. I see big differences when trying to model vertical arrays destined to work on ground and modeled in "free space", different pattern and just plain ridiculous to do that. I know from my hardware experiments with Razors (quad - yagi) that if I changed height of the boom and I reoptimized the spacing/dimensions I would get different configuration. So my conclusion was that antenna has to be designed for the height it is going to be used at. Closer to ground, the more pronounced effect. What I am trying to say and not sell anything, is that perhaps the ground effect and rhombic's spread over it over few wavelengths might have something to do with it's good performance. Maybe it does... but I tend not to believe such things unless they come with good solid reasons. I think that software modeling is a great tool, but I also know that it can not capture all the variables and effects that are happening around antennas, the ground and the sky. All I am pointing out that based on mine and other's experience, rhombic is a great antenna, performing perhaps better than modeling shows (W8JI web site downplays it). If I get the chance, I will try to do some real life tests and comparisons on HF. We have some 30 rhombics, some phased side by side and will try to model and compare them with other antennas. BTW our rhombics have a load resistor made of open (resistive?) wire stub, folded few times back and forth. They were used with 50 kW transmitters. see http://www.teslaradio.org/site_survey.htm I am just trying to bring attention to possible discrepancy that perhaps is worth exploring. If some believe in gospel of modeling and paper antennas, than enjoy it. I prefer reality. I don't ever see that as an "either-or" choice - I am not comfortable until both viewpoints agree. If modeling and 'reality' observations do not seem to agree, it means we're still missing some pieces of the puzzle. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Rhombics
Yuri, K3BU wrote:
"All I am pointing out that based on mine and other`s experience, rhombic is a great antenna,---." Agreed. I worked for an oil company on Tierra del Fuego. We frequently had no contact with our office in Buenos Aires. I put up a rhombic driven by a 20-watt Hallicrafters transmitter surplus from our Bolivian operations. They had upgraded to Collins 30-K5 transmtters there. The Argentine Post Office used a surplus 300-watt BC-610 into a dipole near our camp. When I called the same station in Buenos Aires used by the Post Office, they at first would not believe that I was as far away as Tierra del Fuego. Best regards, Richard Harrison, KB5WZI |
Rhombics
Sorry I mis-spoke in my story about Tierra del Fuego. The power into the
rhombic and dipole was about the same. Despite the size difference between a Hallicrafters HT-20, and the military surplus BC-610, both put out about 100 watts on AM. Best regards, Richard Harrison, KB5WZI |
Rhombics
In article ,
Cecil Moore wrote: Jimmie D wrote: Back in the 70s a friend and I put up a rhombic antenna in a pecan orchard on 11M. If I remember correctly each leg was about 8 wl long. Isn't that an illegal antenna on 11m? :-) Not back in the 70's........ |
Rhombics
Ian White GM3SEK wrote:
. . . What is undeniably true is that it *looked* spectacular! I've used many kinds of antennas since then, up to an 85ft dish, but not one of them has given me the same buzz as that rhombic. And there is the trap: buzz isn't the same thing as performance. . . . As always, Ian put his finger directly on a fundamental principle. The problem with modeling programs is that they don't model the buzz. Roy Lewallen, W7EL |
Rhombics
Yuri Blanarovich wrote:
. . . Spacing two antennas few wavelengths can give us diversity effect by the virtue of propagation and waves hitting them differently. Rhombic is kind of antenna/feeders spread out over few wavelengths over ground. Perhaps there is also some of traveling wave mode going on, like in a Beverage. You can't simulate that . . . NEC-based modeling programs don't have any problem simulating a Beverage and its traveling wave operation -- they do quite well at it. MININEC-based programs, no longer in wide use, weren't able to because of the use of perfect ground during impedance and current calculations. Roy Lewallen, W7EL |
Rhombics
Ian White GM3SEK wrote in news:bVv
: Alan Peake wrote: Dave Oldridge wrote: Properly designed, they have a good reputation for doing what the theory says they will do. Just remember, though, that you're going to have to sewer almost half your transmitted power into the terminating resistor. But that's the half that would be going the wrong way, basically. But it would get there - eventually :) Long or short path. But I don't know if both paths are ever open at the same time to the same extent. If not, then it may not be a problem. What about running a transmission line from where the terminating R would be, back to the feed point? Assuming you can match it all that is. No problem. Pipe the signal back from the far end into the shack, feed it into a circulator, and add it to the outgoing signal. Cecil will explain what happens to the power :-) Replying to Yuri's point: from personal experience of using a rhombic 100 wavelengths long for 2m moonbounce, it had only about the same maximum gain as a box of 4 mid-size yagis - and that is only while the moon is passing through the very narrow main beam, which only happens for a magic 20 minutes on certain days of the month. In other words, the rhombic did work, but the performance was nowhere near as spectacular as we had expected from its huge electrical length. What is undeniably true is that it *looked* spectacular! I've used many kinds of antennas since then, up to an 85ft dish, but not one of them has given me the same buzz as that rhombic. And there is the trap: buzz isn't the same thing as performance. We need to be very careful about applying dual standards. An unavoidable feature of all very long rhombics is that the main beam is very narrow, because the edges of the main lobe are sliced away by large numbers of sidelobes that are not many dB down. If we saw that kind of E-plane pattern in a yagi, we wouldn't hesitate to call it a "bad design"... so what's "good" about the same feature in a rhombic? Yes, they are much better as HF point-to-point antennas than they are as general purpose. For that kind of service, you can pick your height and rhombic size to specifically service the one path. -- Dave Oldridge+ ICQ 1800667 |
Rhombics
Gene Fuller wrote:
Yuri, I am a bit puzzled by your comment. Ducting and refraction received a lot of technical and mathematical study back at least to the mid-1930's. Terman's books show similar figures to those in your CQ article, and they give numerous technical references from the 1940's. You may have been ridiculed by the amateur radio community, but the pros accepted that sort of propagation explanation many decades earlier. 73, Gene W4SZ Gene, anyone who has been here a while has learned that Yuri knows all, and has discovered all, well except for that other guy. How could you possibly say otherwise? tom K0TAR |
Rhombics
As far as I can tell, Terman describes ducting and refraction relating to
UHF. This was well known in VHF/UHF circles and I mention that in my article. What I tried to point out that this is also happening at the HF frequencies, down to 160m. The closest thing would be Pedersen ray, but that seems to describe relatively short refraction in the layer. All the literature I was familiar at that time showed distorted pictures of Earth and exaggerated height of layers and "bounces". 73 Yuri, K3BU "Gene Fuller" wrote in message ... Yuri Blanarovich wrote: [snip] I am just trying to bring attention to possible discrepancy that perhaps is worth exploring. If some believe in gospel of modeling and paper antennas, than enjoy it. I prefer reality. When I wrote my observations about propagation happening by ducting and refraction some 25 years ago, I was ridiculed. Now the propagation experts are accepting it and playing discoverers (only ON4UN gives me some credit :-). Yuri, K3BU Yuri, I am a bit puzzled by your comment. Ducting and refraction received a lot of technical and mathematical study back at least to the mid-1930's. Terman's books show similar figures to those in your CQ article, and they give numerous technical references from the 1940's. You may have been ridiculed by the amateur radio community, but the pros accepted that sort of propagation explanation many decades earlier. 73, Gene W4SZ |
Rhombics
Gene, anyone who has been here a while has learned that Yuri knows all, and has discovered all, well except for that other guy. How could you possibly say otherwise? tom K0TAR If that is all you learned, I pity you. I don't know many things, especially what is eating you. I simply describe my experiences and express my opinions. You could do that too and argue technical points rather than spewing crap. I think you might be confusing me with W8JI :-) 73 Yuri |
Rhombics
I assumed that your VHF rhombic was perhaps high and maybe even rotatable.
I do not have measurements and evidence, just anecdotal evidence using one, hearing from other users and based on some comments on the subject and experiencing some discrepancies with modeling, just speculating that there is something to it. If all those who never used rhombic, but modeled its performance and are convinced that that's it, then I rest my case. I will have chance to run some test and will report, if it doesn't annoy K0TAR. 73 Yuri, K3BU "Ian White GM3SEK" wrote in message ... Yuri Blanarovich wrote: OK on Ian's rhombic experiences on V/UHF, but that I believe would be different situation, I.e. rhombic not working in conjunction with ground reflections/effects. With "normal" HF rhombic we have a situation where antenna is spread out over few wavelengths and interacting with ground. The same is true at VHF. All rhombics interact with ground, because their length is many times greater than their height above ground. The number of wavelengths above ground will change the details, but not the basic fact. Spacing two antennas few wavelengths can give us diversity effect by the virtue of propagation and waves hitting them differently. Rhombic is kind of antenna/feeders spread out over few wavelengths over ground. Perhaps there is also some of traveling wave mode going on, like in a Beverage. You can't simulate that Are you quite sure of that? In other words, do you have firm evidence and reasons why? or use VHF analogy being many wavelength away from the ground effects. That analogy was your assumption, never mine :-) Don't forget that skywave polarization is all over and rolling around. I see big differences when trying to model vertical arrays destined to work on ground and modeled in "free space", different pattern and just plain ridiculous to do that. I know from my hardware experiments with Razors (quad - yagi) that if I changed height of the boom and I reoptimized the spacing/dimensions I would get different configuration. So my conclusion was that antenna has to be designed for the height it is going to be used at. Closer to ground, the more pronounced effect. What I am trying to say and not sell anything, is that perhaps the ground effect and rhombic's spread over it over few wavelengths might have something to do with it's good performance. Maybe it does... but I tend not to believe such things unless they come with good solid reasons. I think that software modeling is a great tool, but I also know that it can not capture all the variables and effects that are happening around antennas, the ground and the sky. All I am pointing out that based on mine and other's experience, rhombic is a great antenna, performing perhaps better than modeling shows (W8JI web site downplays it). If I get the chance, I will try to do some real life tests and comparisons on HF. We have some 30 rhombics, some phased side by side and will try to model and compare them with other antennas. BTW our rhombics have a load resistor made of open (resistive?) wire stub, folded few times back and forth. They were used with 50 kW transmitters. see http://www.teslaradio.org/site_survey.htm I am just trying to bring attention to possible discrepancy that perhaps is worth exploring. If some believe in gospel of modeling and paper antennas, than enjoy it. I prefer reality. I don't ever see that as an "either-or" choice - I am not comfortable until both viewpoints agree. If modeling and 'reality' observations do not seem to agree, it means we're still missing some pieces of the puzzle. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Rhombics
On Tue, 3 Oct 2006 23:27:56 -0400, "Yuri Blanarovich"
wrote: Terman describes ducting and refraction relating to UHF Hi Yuri, I have a couple of refraction citations made by Ladner and Stoner in "Short Wave Wireless Communications," 1932. They dedicate the book to C. S. Franklin. "Refraction may produce an appreciable increase in signal strength at longer distances and can be expect to produce fading effects similar to those experienced with the longer waves from the ionosphere." How this is achieved conforms to classic ducting, although they neglect to call it such: "Under certain conditions theoretical curves are available from which the field strength at an elevated receiver, produced from an elevated transmitter, may be deduced." 73's Richard Clark, KB7QHC |
Rhombics
Yuri Blanarovich wrote:
I assumed that your VHF rhombic was perhaps high and maybe even rotatable. That thing was 600ft long! Some rotator, that would have needed... a small private railroad maybe? -- 73 from Ian GM3SEK |
Rhombics
On Tue, 03 Oct 2006 12:17:21 -0700, Roy Lewallen
wrote: NEC-based modeling programs don't have any problem simulating a Beverage and its traveling wave operation -- they do quite well at it. MININEC-based programs, no longer in wide use, weren't able to because of the use of perfect ground during impedance and current calculations. Roy Lewallen, W7EL Roy, I think you'll find that Antenna Model (a MININEC based program) can model a Beverage quite well. . Danny, K6MHE |
Rhombics
"You" wrote in message ... In article , Cecil Moore wrote: Jimmie D wrote: Back in the 70s a friend and I put up a rhombic antenna in a pecan orchard on 11M. If I remember correctly each leg was about 8 wl long. Isn't that an illegal antenna on 11m? :-) Not back in the 70's........ I didnt think it was either. We belonged to a club back then that stressed playing by the rules. As a result of this there were a lot of people playing with antennas. I did witness an intersting phenomenom with this antenna. The beam of the antenna was nearly perpendicular to I-75 and sometimes we could hear truckers as they passed though the main lobe. Over a period of time we were able to deduce that the area of reception was only about a mile wide at this point. Jimmie |
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