Hello all.
My OMNI V has decided to become noisy on RX, especially 40 & 30m but =
also on 160m.
The noise is intermittent of course!
It sounds like thunderstorm QRN on 160m and peaks around S9+10.
But on 40 & 30, it usually just raises the noise floor to around S3-5 =
without the bangs and crashes I have on 160.
I'm pretty sure that all bands are affected, it's just that the effect =
is far more noticeable on the bands mentioned. Surprisingly, it doesn't =
appear to affect 10m or 80m much.
The thunderstorm QRN noise also appears on bands other than 160, it's =
just loudest on 160m, and still present on 160 when 40/30 have the =
raised noise floor. For some strange reason, 80m is relatively =
unaffected even when 160/40/30 are seriously affected!
Please note that all of these observations made with a dummy load =
connected :-)
The problem will sometimes occur right from switching the radio on, but =
can also occur after minutes or even hours of faultless operation.
40m appears to be the favoured band, with the S meter sitting at around =
S3 or so with a dummy load connected.
I did repair a problem with the VCO about a week ago. The symptom was =
that the PLL would lose lock without warning, with the usual "chirp" =
noise as it went. I discovered that the VCO block was mechanically =
sensitive, so soldered all the joints in the area bounded by the =
screening can. This has provided a complete cure so far.
I've checked very carefully for solder bridges etc. on the board just in =
case the RX noise problem is self inflicted. I cannot measure or see any =
at all.
The RX noise problem did not begin until around 4 days after the VCO =
resoldering job.
I can also detect some noise on TX as well. With the OMNI in tune at =
minimum power out into a dummy load, I can hear the same noise as I have =
on RX on a monitor receiver, after taking out the beat note on the =
receiver with the notch filter. The magnitude of the noise is very much =
lower than on RX though, and no on air complaints have been had about =
noisy audio / frequency jumping / FM'ing etc.
So I am assuming that the noise is being generated in the PLL / VCO =
somewhere, and was wondering if anyone has had a similar fault before, =
especially any of you tech guys at T-T.. I'd be grateful for any hints! =
:-)
I have not had the opportunity to make any DC measurements or look with =
my 'scope yet, I thought I'd ask here first and see what the consensus =
is.
One last clue: despite the enormous noise occasionally, the PLL never =
loses lock, neither can I hear the VCO being pulled around. RX signals =
are clean and pure, as long as they make it over the noise floor
Mechanical shock does not influence the noise at all either.
Thanks for any input on this!
Paul MW0CDO..=20
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