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Chuck, WA7RAI wrote:
"I get the impression that what you are doing is placing any number of elements on a .1 lambda boomlength in order to determine if the close proximity EM interactions produce more gain than just the standard 2 elements would on that same boom length." Close element spacing was once used to make a class called supergain antennas. Kraus notes in his 1950 "Antennas" that: "Until the antenna power was considered by G.H. Brown (Proc. I.R.E. January, 1937) the advantages of closely spaced elements were not appreciated." The W8JK array by Kraus is closely spaced. Kraus notes a downside: "Hence, a considerable reduction in radiating efficiency may result from the presence of any loss resistance, (The radiatiation resistance drops as spacing shrinks.)" See "Antennas" edition 3 for close spaced antennas. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote in message ... "Hence, a considerable reduction in radiating efficiency may result from the presence of any loss resistance, (The radiatiation resistance drops as spacing shrinks.)" See "Antennas" edition 3 for close spaced antennas. Best regards, Richard Harrison, KB5WZI Hi Richard, Indeed. And Kraus' speculation in this regard has been the basis for some debate, if I recall. It is my opinion that .1 lambda spacing has been somewhat established as optimum spacing for a 2 el yagi with a director - and I get the impression that this is the basic structure that Art is using as a benchmark. Perhaps the next step is to determine whether the modeled gain Art is getting is a result of artifacts or not. 73 de Chuck, WA7RAI |
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"Chuck" wrote in message news:DCyed.11049$6P5.8562@okepread02... wrote in message news:oYeed.289823$MQ5.38322@attbi_s52... YES Hi Art, snip. If you haven't already done do, I would be trying frequency sweeps over a limited bandwidth, and scaling them to higher frequencies to see if the results remain consistent. If not, this could be an indication of artifacts. I'l think about that I get the impression you are making physical models to test as well. Perhaps scaling to a much higher freq, say 50 or 145 mHz or so, would make FS tests more manageable. The goal, is to simply determine if the gain of the experimental structure is greater than that of the benchmark (the 2 el yagi) - measuring the exact amount, should be of no real concern at this point. 73 de Chuck, WA7RAI Chuck, I am an experimentor, I am not advocating changing the aproach to antennas by amateurs When light weight fishing poles on E Bay became less than a dollar a foot I was able to get rid of most of my aluminum stock.When I got Beasely's NEC Pro program all prior constraints regarding antenna experimenting were removed (ala aluminum or copper foil). Last year I made a 160M dipole that was rotatable and frequency controlable with moveable bandwidth, I succeeded, but it still was a large structure and winter provided many unwanted occasions to repair the unexpected. This winter I am being less ambitious and am confining myself to a 8 foot boom. First I was to check if more elements can improve the gain. From prior experiments I knew that feed impedance can be change upwards by placing an element close the rear of the feed dipole which is contrary to the ARRL handbook. I also was aware from previous experiments that element diameter was very important if one is not controlled by mechanical requirements. I also knew from reading that in stacking when only the bottom array was being used one obtained protection from static noise so this would also be a good opportunity to have one element say 30 inches higher than the rest on the mast which would be part of the original array to give room for experimentation. My present model has a gain of 13 dbi at a ht of 820 inches over perfect ground and is less than 2:1 across the audio portion of 20 M. The number of elements is six which suggest things are heavy but with fishing poles it is extremely light. ( note, fishing poles when ice laden bend as if it had caught a fish and the ice then slides off) I have not used the f/b to rest upon as I believe that the lower lobe at the rear is not important where the second lobe is when considering direction of propagation. So thats it Chuck, I enjoy myself with playing with antennas to find out things for myself as I have more options at hand that the ARRL have not considered as yet and thus are not held hostage to the knoweledge of the many psuedo experts who thou knoweledgable about the past which is very usefull have decided that there is no future since all is known. By the way with the advent of cheap cameras $30 it is easy to place a SWR meter or power meter right at the feed point and eliminate questions regarding transmission lines. Regards Art |
"Chuck" wrote in message
A reduced-noise (E-field loaded) vertical for 40m with a VSWR bandwidth of 1.3:1 from 7.0 to 7.3 mHz, (it's not a dummy load as one would generally deduce from the above description), and has proven to be as good a performer on DX and local as my conventional top loaded vertical. What is E-field loaded? Not sure what you mean with that... The conventional vertical sees a noise level here of around S-7 or greater, and the E-field loaded vertical, around S-3 to S-5 (on IC-756, normal BW, no NB, no DSP). I'd be very leary...Also would depend on the polarization of the noise, and any possible changes in the pattern...But in general, if a certain vertical picks up more far field noise than another, it's the superior vertical. Noise is rf like any other signal. So unless I'm missing something here, the conventional antenna should also receive the *desired* signal better than the low noise version. And being things are generally reciprical, it should probably transmit a better signal also...How careful have your on the air tests been? Are you quickly A/B'ing using a switch? Needless to say, I'm kind of dubious of the claims of equal performance. Unless the noise was common mode or polarity related, I've never seen an antenna that received lower noise, outdo one that picked up more noise. If the change is not efficiency related, that would leave me to think that your vertical pattern is being skewed somewhat, and is more horizontally polarized than the other, and thus , picks up less vertically polarized noise. If thats not the case, I would think the low noise version is less efficient. Just my opinion tho... Neither of these were developed using computer modeling, though. Neither were my comments...:/ MK |
"Chuck" wrote in message news:B3Ted.11167$6P5.7719@okepread02... wrote in message news:MzAed.448084$Fg5.138935@attbi_s53... "Chuck" wrote in message news:DCyed.11049$6P5.8562@okepread02... wrote in message news:oYeed.289823$MQ5.38322@attbi_s52... YES Hi Art, snip. If you haven't already done do, I would be trying frequency sweeps over a limited bandwidth, and scaling them to higher frequencies to see if the results remain consistent. If not, this could be an indication of artifacts. I'l think about that I get the impression you are making physical models to test as well. Perhaps scaling to a much higher freq, say 50 or 145 mHz or so, would make FS tests more manageable. The goal, is to simply determine if the gain of the experimental structure is greater than that of the benchmark (the 2 el yagi) - measuring the exact amount, should be of no real concern at this point. 73 de Chuck, WA7RAI Chuck, I am an experimentor, I am not advocating changing the aproach to antennas by amateurs Hi Art, I apologize if I gave that impression. When light weight fishing poles on E Bay became less than a dollar a foot snip A 2:1 VSWR bandwidth over the 20m phone portion implies a good Q, but aren't you even a bit curious if the gain is indeed as high as 13 dBi? Funnily today I changed the model slightly and the gain exceeded 14 dbi with an increase in Q So this is the model that I am going to make but with the anticipation that by curving the elements I will narrow the beam width. It shows 66 degrees at the moment and a take off angle of 12 degrees. It should be up in a few weeks. When I test I will look for feed impedance and lobe width using a laptop program with a distant signal. I seem to recall from years ago, a yagi that had several close spaced directors on a relatively short boom - I just can't recall if it was commercial, in an article, or any other significant details about it. It may have been the 13 element I made for 20 M on I think a 80 foot boom and that was the first time I used two reflectors to get a 50 ohm feed. I seem to remember that Roy modelled that also on EZNEC or is it ELNEC and he confirmed the 50 ohm feed as did my modelling and the actual antenna.This was about 10 years ago. So thats it Chuck, I enjoy myself with playing with antennas to find out things for myself as I have more options at hand that the ARRL have not considered as yet and thus are not held hostage to the knoweledge of the many psuedo experts who thou knoweledgable about the past which is very usefull have decided that there is no future since all is known. By the way with the advent of cheap cameras $30 it is easy to place a SWR meter or power meter right at the feed point and eliminate questions regarding transmission lines. Regards Art The camera idea is a good one :) Yes I first used a micro video camera for direction of my prop pitch rotor and then to observe stepping motor angles on capacitors There are always new things to learn... My latest experiments have produced some unusual antennas: A unique dipole that does not inductively couple with surrounding conductors (the perfect attic dipole), that can be 'tuned' at ground level, which, at first glance, appears to have a somewhat omni- directional pattern. A reduced-noise (E-field loaded) vertical for 40m with a VSWR bandwidth of 1.3:1 from 7.0 to 7.3 mHz, (it's not a dummy load as one would generally deduce from the above description), and has proven to be as good a performer on DX and local as my conventional top loaded vertical. The conventional vertical sees a noise level here of around S-7 or greater, and the E-field loaded vertical, around S-3 to S-5 (on IC-756, normal BW, no NB, no DSP). Neither of these were developed using computer modeling, though. Keep up the fun... Well that seems all very interesting but you are very much out of my league which is just as well because mention of E and H waves agitates the experts more than my talk of coupling does Art 73 de Chuck, WA7RAI |
Chuck, WA7RAI wrote:
"Indeed. And Kraus` speculation in this regard has been the basis for some debate if I recall." Kraus gets support from Terman`s 1955 edition on page 906: "A characteristic of all close-spaced arrays is that as size to antenna gain is reduced, the radiation resistance also goes down; this is illustrated by Fig. 23-36." Best regards, Richard Harrisopn, KB5WZI |
Richard Harrison wrote in message ... Chuck, WA7RAI wrote: "Indeed. And Kraus` speculation in this regard has been the basis for some debate if I recall." Kraus gets support from Terman`s 1955 edition on page 906: "A characteristic of all close-spaced arrays is that as size to antenna gain is reduced, the radiation resistance also goes down; this is illustrated by Fig. 23-36." Best regards, Richard Harrisopn, KB5WZI Hi Richard, No one can argue with Kraus and Terman or anyone else on this. What is "debatable" is: at what point does radiation resistance become too low - where high current losses cancels any gain achieved by the tight coupling. This is JMO, of course. 73 de Chuck, WA7RAI |
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