Rob
Seems most people using a UNUN (myself included) are using it to transform
the 50 ohm feedline to match a low or high Z (but resonant) antenna such as
a ground
mounted vertical or inverted L. I used a short (12" long) section of rg213
from the UNUN to
the antenna (about 20 ohms at the feedpoint of my 160m inverted L).
Impedence at the end of a
coax cable depends not only on the impedence of the cable but the frequency
versus wavelength.
Remember the old saying: 1/4 wave transforms, 1/2 wave repeats.
Anything in between will depend
on the wavelength.
Don't worry about stupid questions....watch out for stupid answers (like
mine)..HI..HI.
JerryC
KC8TES
----- Original Message -----
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
To: <towertalk@contesting.com>
Sent: Friday, November 12, 2004 12:40 PM
Subject: [TowerTalk] I have a really stupid question (baluns and ununs)
> 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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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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