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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