[TowerTalk] Amidon UNUNs

[Keith Morehouse - W9RM]

WR34SHE@shellus.com wrote:
> 
> I bought about 500 feet of catv cable that is direct bury.  I plan on
> using some UNUNs from Amidon to convert from 75 to 50 ohms and was 
> wondering if anyone else has used them?

I use Amidons BALUNS (1:1's), made from the Jerry Sevick designs, with
good results, electrically, on my beams.  I've run legal limit on 20 and
15 - no problem.  I assume the materials are the same in the UNUN's.  

Beware of mechanical gremlins on these designs.  I had several units
fail in the air because of vibration.  HyGain 204BA's are notorious
vibrators and actually loosened the internal nuts attaching the
transformer assemblies to the ceramic feedthroughs on the "BAL" side. 
When I took the box down and opened it up, all the internal connections
were unhooked and there was a handful of hardware loose inside. 
Locknuts and double nuts cured the problem.  With the UNUN's, most
everything is probably soldered, so the chances of this happening are
less.

Question.  Why are you going to the expense of the 50/75/50 ohm
impedance change ??  I run CATV hardline from the shack to the antennas
(150') with no attempt to match.  Sure, I see the slight mismatch but,
with the ultra low loss of the big 75 ohm cable, it's meaningless.

> Also there was something on the reflector about a place that had cable 
> ends for catv.  I will make them if needed but am curious as to what 
> one already made up costs.

Gilbert Engineering in AZ.  CATV connectors are C H E A P !!  The
problem is the $100 minimum order.  A hundred bucks gets you a lot of
connectors if we're talking 0.5".  Of course, with REAL cable, you get a
lot less for your hundie..

They may not want to talk to you if they figure out you're just a low
life ham.  Make sure they understand you work for a big utility company.
BTW, they sell the official cable prep tools too !  I bought one for
0.5" and one for my big, low loss stuff.  The 0.5" one was only about
$30.  Don't ask about the other one...<ugh>.  Better then hack saws and
razor knives though - 'specially when you're gonna dump big power
through them (they're REALLY not made for that...although they work
fine...)

As they say in Coors land - Good Luck !

---------------------------###-----------------------------
PROBE ELECTRONICS 100 Higgins Road, Park Ridge IL 60068 USA
Keith J. Morehouse /  W9RM  / Society of Midwest Contesters
847-696-2828  FAX: 847-698-2045  e-mail: blckhole@ripco.com
---------------------------###-----------------------------

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