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

To: "Rob Atkinson, K5UJ" <>,<>
Subject: Re: [TowerTalk] I have a really stupid question (baluns and ununs)
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Fri, 12 Nov 2004 14:21:40 -0500
List-post: <>
> 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.


In order to transform impedance the bump has to occupy some
distance in terms of  wavelength. In order to have a large
effect, the bump also has to be big.

The bigger the bump and the longer the bump, the more effect
it has on the system.

In a UHF connector, just like in my marriage, the male is
always perfect. It is the female that causes all the
problems. The impedance bump in the female UHF chassis
connector is roughly about 1/2 inch long. They also
typically are around 30 ohms or so Z0. That's UHF connectors
work fine all the way to lower UHF. The mismatch isn't big,
and it is VERY short.

There are indeed 20 ohm transmission lines. I even have so
15 ohms and lower Z transmission lines. But they are not
needed if leads are short. Most lug or wire connections are
in the hundreds of ohms!! Even they are not a problem.

Think of it this way, if the line is really short in terms
of wavelength, the standing waves have no place to stand.
Just keep the leads short.


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