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#11
June 11th 06, 09:36 PM
posted to rec.radio.amateur.antenna
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Noise level between two ant types
Ian White GM3SEK wrote:
Tom Ring wrote: wrote: How many Yagi's have floating driven elements without ground paths? None on VHF/UHF/SHF that I build and anyone I know builds. Maybe on HF it's different. I don't know why it should be, though. Although normally all the other elements float on anything but 6 meters. You're both over-generalizing. In VHF/UHF/SHF yagi construction it's quite common to find driven elements connected to the boom or floating. The same choice or a different choice may be made for the parasitic elements. There are many different reasons for these choices, including: * size of elements and boom * mechanical strength requirements * effect of boom on element resonance (depends on mounting method) * long-term effect stability of element resonance * feed impedance of driven element (affects choice of feed method) * number of elements involved * perceived or actual effects of "static". This makes the choices quite complex, and makes generalization impossible. Quote an example, and someone else will quote you a counter-example. Just one other thing: PLEASE let's not talk about elements being "grounded", way up there at the top of a tower. Maybe I should have defined what I meant when I said floating. I think we have been talking about a DC grounded element, and that's what I meant with respect to floating. Virtually all of the homebrew yagis that I have seen, and most of the commercial are gamma match, or T match. The gamma is not going to carry the ground through, but is used almost exclusively on 6 meters where driven elements are rarely insulated from the boom. 2 through 432 are T matches and that DC grounds the driven element regardless of how it's mounted. Going up we see mostly loop yagis, and I've never seen one of those that's not grounded. I know there are regular (non-loop) yagis used 902 and up, but I never seen one to see how they are driven. So, for me anyway, the generalization works. And I'm just watching Silverstone, Ian, so don't tell me how it went! tom K0TAR |
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