[TowerTalk] I have a really stupid question (baluns and ununs)

[Rob Atkinson, K5UJ]

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 
this question:

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.

tnx
rob/K5UJ

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