Rob,
It may have cost you more $$$, and more effort, but YOU DID THE RIGHT
THING... Your description sounds like a clean, well thought-out scheme...
and it WORKS...! BTW, the Radio Works line isolators are the best devices
to use for ANY installation.
73, Larry - W1GOR
----- Original Message -----
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
To: <mark@microenh.com>; <tentec@contesting.com>
Cc: <k5uj@hotmail.com>
Sent: Tuesday, May 20, 2003 13:32
Subject: [TenTec] Omni VI/3 rf feedback
> I think Mark said his problem is on all bands; not just 12 m. When I got
> back on HF about 18 months ago after being off for many years, I ran my
Omni
> with a goldline mic right out the house er, tx site, to my vertical, a gap
> titan. The omni was grounded to a cold water pipe with a thin run of
tinned
> braid, which I figured was good enough. It had worked in the old days
with
> my tube rigs. I'd soon learn that the new(er) solid state rigs are more
> touchy about grounding. Working an old friend on 10 meters one day, he
> remarked that my audio was fuzzy and told me I probably had rf feedback
> which was a new thing to me. I blew it off since he was the only one to
> tell me this (but a lot of hams will tell you you sound great when in fact
> you sound awful--I attribute this to different standards) but when I put
my
> centurion on the air a few months later, I couldn't work anyone because
the
> rf had become too distorted for anyone to understand me with the higher
> power level. After doing a lot of reading, phone calls to people at gap
> antennas and radio works and experimenting, here's what I learned and what
I
> did at my place to fix my problem.
>
> First, TT says in the Omni manual that a good ground is needed (or words
to
> that effect). They should put that in bold type. I've since talked to a
> few other omni owners with the same problem and therefore think this is
> going on in a number of QTHs and it all has to do with the installation.
>
> The first thing to go was the cold water ground. I moved my shack to a
> basement window, and ran 6.5 feet of copper cable outside to five 8'
ground
> rods, one in the center and 4 each connected directly to the center one
(not
> daisy chained). I had tried being lazy and running 22 feet of 2/0 cable
> across the basement to the rods but quickly found the 22 ft. of ground run
> was another antenna--no dice. Next I dumped the ground bus bar, a 6'
copper
> pipe (almost another antenna on 10 meters) and hooked a 1 foot copper pipe
> to the ground cable coming in to the shack to use as a contact point.
This
> pipe sits right behind my transmatch and amp. they are connected to it
with
> 6" runs of heavy gauge 1" wide braid. all other ground runs to the rigs,
> p.s., are with this same type braid (available from cablexperts) coming
way
> from the pipe. Each piece of gear has its own separate run -- no daisy
> chaining with one ground run. Next I wrapped the mic cable at the omni
> input around 3 ferrite chokes and did the same with one or two chokes
(which
> are available from RF Parts, San Marcos Calif.; they have the best prices
> and quality for split 1/2 inch i.d. chokes in plastic holders) on just
about
> every wire going in and out of the Omni. Lastly, I put Radio Works line
> isolators in the feedline between the exciter and the amp, between the amp
> and the transmatch, and at the feed point of the gap vertical. This was
to
> bust up ground loops circulating, between all the devices in the rf chain,
> on the feed shields and ground braids. Now my rf is clean enough to eat
off
> of.
>
> Overkill? Probably. The alternative (if you have the time) is to try
each
> supression technique one at a time while txing into a dummy load &
listening
> on a separate rx until you find the least number of measures that are
> effective. Since I didn't have time (and patience) for that I went for
> overkill, but I have to admit the other way would have been cheaper. Hope
> this helps anyone with an Omni rf feedback problem.
>
> 73,
>
> Rob Atkinson
> k5uj@hotmail.com
>
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