Rob,
I use 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
antenna. These line isolators are perfect for curing the kind of problems
(RF loops and feedback) that you describe. Go to the Radio Works web page
for full information and some clever ideas to prevent this kind of problem
from occurring again. A tuned interface is not needed...!
73, Larry - W1GOR
----- Original Message -----
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
To: <tentec@contesting.com>
Cc: <k5uj@hotmail.com>
Sent: Tuesday, May 20, 2003 14:07
Subject: [TenTec] Omni VI/3 ALC problem?
> Okay, now it's my turn with an Omni VI question.
>
> I have been having some trouble driving the Centurion to full output on
some
> bands with the Omni VI. Originally, the problem was driving it to 1200
> watts on 40 meters (it was fine on 80). It always went to 1200 watts or
> more on CW during tuneup but on phone on 40 it would peak out at about 900
> watts. As I wrote a few weeks ago, I thought I'd fixed it by shortening
the
> feedline between the exciter and amp. It turns out the problem is a
moving
> target--the shorter feed caused it to simply pop up on a higher frequency.
> I put a swr analyzer on the end of the feed to the amp and keyed the amp
so
> the analyzer would be looking at the feed going to the tuned inputs so I'd
> see what the rig sees when driving the amp. I found that on good bands
> there was no reactance on the line. On poor drive bands there was a
> reactive component of about 10 ohms (+- 2). In all cases the swr was
always
> very low (naturally--remember swr alone doesn't tell the whole story!).
My
> theory is that on phone, this X somehow causes the alc to kick in too much
> and limit the rig output but that sure seems like a stretch. No probs on
cw
> and the Corsair II drives the amp fine. Any ideas for a solution? All I
> can think of is a matching network between the amp and the rig which I'm
not
> much interested in (I guess I could use one of those autotuners but I'd
like
> to drive the amp without another tank circuit to fool with), or maybe
> there's an ALC adjustment?
>
> If ur about to tell me to relax and live with it don't bother--I'm aware
of
> that as a solution and I'll do that if I have to, but for now I'm
interested
> in getting some practical troubleshooting ideas for when I have some time
to
> kill (it's more of a mild annoyance--not a high priority). I also know
that
> 300 watts is some tiny fraction of a db gain--don't need to be told that
> either.
>
> tnx everyone & 73,
>
> Rob Atkinson
> k5uj@hotmail.com
>
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