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

[Barry Scott]

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