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Richard Clark wrote in
: The gain of the 15 foot noise reducing vertical is about -15 dB reference: http://www.kongsfjord.no/dl/Antennas...ntennas%20For% 20MW,%20LW,%20And%20SW%20rev%202.pdf In a brief review of the article by the name found in the Subject line, I came across this bare quote offered above. It contains not one, but two unsupported claims that seem to be commonly encountered in the Short Wave Listening community. The first that is more easily supported or denied is the gain claim of -15 dB. Where does this loss come from? Without any substantiation beyond the inference of comparison to "active antennas," it seems to be lost to indirect references in other writings. However arrived at, this claim is suspicious in the extreme - unless it is a vague and offhand substitution for antenna system gain which goes to the heart of the matter of a poor ground system. If so (the loss is found in the absence of an adequate counterpoise), that is indeed low hanging fruit that has been left rotting on the limb. As for the noise reducing claim, this, too, appears to arrive through indirection or muddied with discussion of active systems. I can only surmise that the lowered noise was the noise of the added circuitry of the active antennas. If you discard the amps, I suppose you can claim you've improved the noise which brings us to the Gordian knot of the low gain needing those amplifiers - most curious writing. At least one person has claimed that noise reducing antennas are noisy. But when I quizzed him about his implementation, it turned out that he had not implemented the antenna correctly. If you do not follow the instructions, then you may end up with a noise increasing antenna like he did. Good reporting would have described the defect so that the solution could be observed as rational rather than prescribed. much to my amazement, that long coax (50 feet) lead often degrades 2nd order intercepts of active whip antennas by 20 dB or more and degrades 3rd order intercepts of active whip antennas by up to 10 dB, depending on the type of active whip antenna. It would appear that "depending on the type of" antenna begs the question why coax is the culprit. I can see how this kind of writing spawns a new superstition of the superiority of twin lead. More could be said about Common Mode suppression (which the designs on this page do NOT entirely address). 73's Richard Clark, KB7QHC I don't know enough to query actual figures there, but I see the scheme as simple worth a try even without the amps. I've seen the term 'noise reducing' questioned, and I think rightly, but if it's just relative, if he has found the scheme to be less noisy than other schemes, he might just be using the term to indicate that. I do think the writing leaves gaps that should be filled, but again I figured that building it was easy to try. And I can always ask him, but I won't do that without setting up enough of it to test what I learn. Similarly I don't know any reason to assume the twin line is superior to coax. My provisional assumption is that its lack of direct contact with anything means that it probably isn't any worse. If it was, I think he'd have discovered that so obviously that he wouldn't be sticking his neck out like this. |
#2
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On Sun, 03 Jan 2010 13:37:42 -0600, Lostgallifreyan
wrote: I see the scheme as simple worth a try There are a world of such schemes, and very little time in the span of our short visit to this vale of tears. First principles always satisfy and should be given primacy. 73's Richard Clark, KB7QHC |
#3
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Richard Clark wrote in
: On Sun, 03 Jan 2010 13:37:42 -0600, Lostgallifreyan wrote: I see the scheme as simple worth a try There are a world of such schemes, and very little time in the span of our short visit to this vale of tears. First principles always satisfy and should be given primacy. My aim is to find something in a practical situation that demands compromise. Even if I learn all the principles I can't expect to apply an ideal, so I'm looking for schemes that might save time in finding something that works for me. They can't all be misses. At least this one consists of parts I can easily reuse. ![]() |
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