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

[Jacques Fortin]

Hi Barry,

The common crystal, yes (Y401).
The other possible suspect is the silver migration disease in one of the tuning coils capacitors.
Meaning in Z213, Z207, Z201, and even T201: all those ones are used on the 0.5 - 1MHz band only.
And the prime suspect capacitors are those with a working DC potential (even if it is a small one) across.
Like C233, C254...

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
Envoyé : 22 octobre 2024 11:24
À : Jacques Fortin <jacques.f at videotron.ca>
Cc : R-390 Mailing List <r-390 at mailman.qth.net>
Objet : Re: [R-390] High Noise Floor in 0-1 MC Band

Hi Jacques,

Shorting both antenna jacks eliminates most of the noise; however, there's still a small noise increase when switching from the 1-2 MC band to the 0-1 MC band.  I even tried putting the top cover back in place to help eliminate stray noise from getting in through the top but I couldn't notice any difference with it on as opposed with it off.

The 6-7 MC band has the same noise level as the other bands.  I think you were probably looking at the common crystal for that, right?

Given this, perhaps there just a high level of atmospheric or other noise at my location.  I experimented a bit with my Grundig Satellit 800 and, while the two receivers aren't nearly in the same class, I don't notice that much difference in, say 600kHz and 1200kHz so still not sure if it's atmospheric.

Thanks,
Barry - N4BUQ

> 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