|Subject:||[TowerTalk] I have a really stupid question (baluns and ununs)|
|From:||"Rob Atkinson, K5UJ" <firstname.lastname@example.org>|
|Date:||Fri, 12 Nov 2004 17:40:17 +0000|
Okay, I have what must be a stupid question. I say that because I have
looked for an answer and have been unable to find one, so the answer must be
so obvious that I'm not seeing it and everyone else knows it. Well, since I
have embarrassed myself before and surely will again and therefore don't
care about my reputation since I never had one anyway, I am going to ask
We commonly use ununs to transform one feed impedence to another, or transform an unbalanced feed impedence to the feedpoint Z of an unbalanced antenna. The commercially available ununs have UHF females on each side of them, which makes sense in the case of the 1:1 ununs and the ones that are designed to transform 50 to 75 ohms which are common unbal. feed impedences.
I see a few ununs on the market that seem to be intended to work with very low unbalanced impedences such as 5, 10 or 20 ohms, and they too all have UHF females. This does not make sense to me since as far as I know, there are no 5, 10 or 20 ohm coax feed products out there that are commonly available. unless someone is working with some sort of complex arrangement of 50 ohm feeds in parallel, these ununs are usually placed at the feedpoints, as in for example a vertical that has a f.p. Z of 10 or 15 ohms, right? I'd appreciate it if someone would explain to me why a 50 to 20 ohm unun has a UHF female on the 20 ohm side, since I don't know of any 20 ohm coax, instead of a pair of lugs. If at the feedpoint, do you simply defeat the purpose of the UHF connector by clamping the counterpoise to the threads and stick a short jumper to the vertical in the center? There's something wrong with this picture I'm missing.
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