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Re: [Amps] rfi

To: amps@contesting.com
Subject: Re: [Amps] rfi
From: Manfred Mornhinweg <mmornhin@gmx.net>
Date: Tue, 01 May 2007 17:29:21 -0400
List-post: <mailto:amps@contesting.com>
Hi guys,

I'm having a lot of fun reading all those RFI stories. My own experience 
instead is rather drab! I run legal limit from my apartment, and don't 
seem to interfere anything at all. I can run the computer to do SSTV or 
RTTY with the amp, I can make a phone patch without the phone picking up 
any RFI, my alarm stays quiet, I can even let the TV run (off air, not 
even cable) and nothing strange happens... And there has never been any 
RFI complaint from a neighbor! How boring!

I want to get my RF out of the antenna, high up on the roof, and not out 
of the feedline, earth connection, AC wiring, etc. For that purpose I 
installed a highly effective current mode balun on my feedline. 15 turns 
on a stack of FT-240-61 toroids.  It works. I get out quite well, into 
ham receivers around the world, but not into local TVs nor other stuff.

An interesting experiment was when I tried to load up the tower on 80m, 
against earth. That was of course without the balun, and having a lot of 
RF radiated from inside the building. Even without the amp, using just 
the 100W radio, I locked up the computer, made the battery charger start 
a fast charge cycle on a full battery, set off the alarm, and made my 
bread machine try to bake a bread out of pure air. It was fun, but then 
I returned to my well balanced antenna and the balun!

Folks, you might want to check what's doing the main part of the 
radiating in your stations: The antenna, or the feedline and power 
wiring! The antenna sure gets out better, and is farther away from 
potential RFI receivers! A dipole with coax feedline and no balun is a 
sure recipe for disaster in this regard. But it can be lots of fun, sure!

Manfred.

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