[TenTec] Problem with Omni V receive sensitivity...

[Tom Scott]

I have an Omni V that I recently purchased from an original owner. He
indicated it was fine, but I'm having some problems with it and thought I'd
post a message to ask if anyone has seen anything similar or has any ideas
about where I might start to look. I got a good enough deal on it that I
don't feel bad if it takes some Ten-Tec factory service work, but I'd like
to try to fix the problem myself.

>From the first day I began using it to receive, I've always felt like it
wasn't working quite right. But I've only this last week finally gotten a
couple of good antennas up to give it a very good signal to work with, so I
have been chalking the problems up to lack of antenna till now. Now I'm
realizing that it has never received a very strong signal, and its receive
sensitivity is very intermittent, sometimes cutting out entirely.

Hooked up to the Omni V I have a Johnson Matchbox with an 80m dipole up
between 35 and 85 feet in the air, fed with well-routed ladder line. I've
also got an 80m Zepp at similar altitude. I've got a good low impedance
ground made with half inch copper pipe. It consists of two sticks of half
inch thick wall copper pipe driven ten feet into the ground. I connected
those together with sweat-soldered pipe right up to three feet from the
station. Then I ran four #6 AWG stranded wires bringing the ground through
the wall to the radio/ps/tuner. Added to that, I've got six 30 foot ground
radials soldered to the half inch copper (even though a dipole shouldn't
need ground radials so much). Like I said, low impedance. I'm also in a
pretty good location, on a local hilltop probably two to twenty miles from
anything higher depending on which way you look.

I've had a few evenings where I've received several pretty good signals,
including some AM shortwave broadcasts on 40m, and general ham QSO's, both
CW and Phone on 80, 40, 20, and 10. I've been keeping a log of most of the
signals I've received, but the strongest signal I've ever received was
peaking at no more than S5. When I am getting good signals, I can tune the
Matchbox by listening to the background static and hear it go up sharply
when I get it tuned right. When I'm not getting anything, there is
background static, but it doesn't change noticeably when I tune the
Matchbox.

Another symptom I've wondered about is the "birdies" that the Omni V is
known for. I have read that these are mostly a problem when you don't have
an antenna hooked up, but I seem to have quite a few pretty loud ones
regardless.

Paul at Ten-Tec told me to hook up  a signal generator and give it 50uV and
see if I get S9 on the meter. I'm going out today to see if I can find an HP
606B to try that, but its clear that something is not right. One thing my
dad suggested I look at is to try to trace the signal through the
transmit/receive relays at the RF front end. I looked at that last night,
but its pretty hard to get to that board. I didn't try to take the back
panel off the chassis, but I guess that's what you'd have to do to get
access to the board better. I do know that the radio sat with minimal use
for a couple years because many of the touch switches have required
exercising to get them to work right, so bad relay contacts might be a
possibility.

This is pretty vague I know, could be lots of things, but anyone have
anything that just jumps out at them? I don't have my 5wpm test done yet
(but trying to get ready, almost there), so I've only been receiving with it
so far. At some point I will break down and send it in to Ten-Tec, but it
would be fun to try to figure out what's up.

Thanks a lot!

- Tom
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       Tom Scott     -    Wyle Electronics    -    KD7DMH
       10300 SW Nimbus Ave #PB, Portland, OR 97223
       503-603-1931 - TEL   503-684-6620 - FAX
       503-504-1583 - Cell    503-604-8651 - Pager
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