John,
Thank you for the info! I spoke to Don at Ten-Tec
about it and he ask me to check between 40 and 20 and
30 and 20 and if there was noticeably more noise on 30
and 40 meters (with no antenna), it could be a problem
with the mixer. I checked it, and there was a very
noticeable difference between the bands, more between
40 and 20, but between 30 and 20 as well. I decided to
order a replacement.
I'm glad you mentioned the heat generated by the
mixer. Maybe over time that heat caused some imbalance
in the diodes in the module. I did noticed what seemed
to be a bit more noise than usual on 40 when I first
got the Omni, but didn't pay too much attention to it,
since 40 can be pretty noisy anyway. Since this
problem raised it's ugly head, however, I think that
some of that noise was being internally generated, and
when I had it on all day, it got bad enough to notice
elsewhere.
Since the bottom cover is fairly thick, I may get
some alumninum stock of the right thickness, attach it
to the mixer and put a little thermal grease on the
top to make contact with the cover. That should draw a
substantial amount of heat away from it. I don't think
the cover getting a bit warm would affect anything
else.
Anthony, NT4X
--- John <jlockj@earthlink.net> wrote:
> Hi Anthony,
>
> I noticed the same thing with my Omni VI a few years
> ago. (My Omni V didn't
> have the noise ramp-up problem) It turned out to be
> the high level mixer
> getting hot. (VERY hot to the touch) With the
> bottom cover off, it the
> symptom never appeared. If let the rig warm up with
> the cover on, then
> removed it, and I "hit" the mixer with some cooling
> spray, the noise would
> drop back down. The easy fix is just to back off
> the RF gain to the 3 PM
> position, or so. (A better fix would be to put some
> ventilation holes in
> the lower cover)
>
> 73,
>
> John W0DC
>
> ----- Original Message -----
> From: "Anthony Bowyer" <adb1x1@yahoo.com>
> To: <tentec@contesting.com>
> Sent: Friday, January 10, 2003 7:31 AM
> Subject: [TenTec] Omni V AGC Problem
>
>
> > After having my Omni V on for several hours (15
> or
> > so), I noted what seems to be a bit of a problem
> with
> > the AGC. There was a definite hiss increase that
> was
> > very noticably mixed with a CW signal I was
> listening
> > to. Turning the passband control more CCW, I could
> > hear quite a bit more hiss than normal. The
> S-meter
> > seemed to be functioning correctly and switching
> > between fast and slow AGC did have some effect,
> but it
> > seemed as if something in the AGC 'system' had too
> > much gain. Looking at the diagram, it seems to be
> a
> > fairly simple design, but I was wondering if
> anyone
> > has had a similar problem with an Omni V or VI (I
> > assume it has a similar AGC system) and repaired
> it?
> > Maybe you could point me in the right direction.
> >
> > Thank you for any help!
> > Anthony
> >
> > =====
> > NT4X
> >
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=====
NT4X
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