[R-390] Calibration issue

[Tim Shoppa]

"Jon" <jonklinkhamer at comcast.net> wrote:
> I'm in the process of going thru electrical calibration on my R390A. I
> noticed a couple of things when I turned on the calibration signal. After I
> zero adjusted it to achieve zero beat frequency I can basically do two
> things in which I would have to zero beat it again. First by just going +/-
> say 50khz (or maybe even less) around the calibration point, in this case
> 09.000  I would have to re zero and there would be a good tone not just a
> little off beat.

This sounds like the dial clutch is slipping. Lots of geartrains out
there have so much grease and grunge on the clutch that I could see this
happening. Also the anti-backlash spring on the Oldham coupler.
And...also see my thread on PTO squirreliness.

> The other observation is by just sitting on the calibration
> mark and returning after about 15 minutes it again would be off. However not
> as bad.

You have to quantify "not as bad". A few hundred Hz of drift from power
on isn't so bad. But as a data point: My R-390A's are stable to +/- 50 cycles
after warmup (measured with a GPS-locked counter - if it says it's off
by 0.1 or 0.001 cycles, then I believe it!)

> BTW the receiver has been warmed up for at least 2 hours in advance.
> I guess I'm trying to pin down whether the BFO or PTO is drifting or maybe
> the 100Khz signal is off.

If the 100kc signal is drifting then you will see a much bigger affect
at 31Mc than at 1Mc (a factor of 31 in fact.)

Also keep in mind that the band crystals and the 17Mc crystal (which
is on below 8Mc) could be drifting too. But again, you'll have to
quantify the drift and find out on which bands it is there/worse.

Tim.