[R-390] High Noise Floor in 0-1 MC Band

[Jacques Fortin]

Hi Barry,
Does it behave the same (higher noise on 0-1 MHz band) when the antenna
input is shorted ?
Just try to understand if it is internal to the receiver or just dependant
on the antenna conditions.
And.. is it also noisy on the 6-7 MHz band ?

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la
part de Barry Scott
Envoyé : 21 octobre 2024 22:26
À : R-390 Mailing List <r-390 at mailman.qth.net>
Objet : [R-390] High Noise Floor in 0-1 MC Band

For the past few months, I've been trying to determine why the noise floor
on the 0-1 MC band in my R390/URR is so high.  If I tune to a strong
station, the noise disappears so, perhaps, "noise floor" might be the wrong
term for it but in places where there's little-to-no signals, the noise is
very noticeable and all but drowns out the weak signals.

If I switch from 0-1 MC to 1-2 MC (or virtually any other band), the noise
is reduced significantly.  The difference can be on the order of
15-20 dB on the carrier level meter.

I presume this isn't normal but maybe it is.  I think someone mentioned that
the noise on the bands under 8 MC are typically a bit higher than the other
bands but that doesn't seem to account for why the lowest band is by far the
worst of them all.

There are only passives that change from 0-1 MC to the other lower bands and
I'm wondering if it's even possible for those to be the problem but I don't
know of anything else that could be causing it either.

I think someone suggested that the 1st crystal oscillator's output might be
low for that band but I seem to recall checking that on the scope and output
for the 1st and 2nd positions seems to be very close to the same amplitude
so I'm thinking that might not be the problem.

Has anyone seen this and possibly have a cause for it?  Like I said, I
presume this isn't normal but I don't know that for sure.

Thanks,
Barry - N4BUQ
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