[R-390] Stability

[Bob Camp]

Hi

If you are on a band where Y201 in the first crystal oscillator contributes, it's got a pretty well documented warmup.It's an AT cut ovenized crystal with turn point up around 85C. That's going to give you a 50 to 70 ppm shift as it heats up. That alone will give you about 1 KHz of drift. It will always go down in frequency initially. It may come back up a bit right at the end.  

The rest of the crystals would do something similar if you heated them up that far. Over the range you do heat them they probably move 10 to 20 ppm. If you are listening to 10 meters, that would give you 300 to 600 Hz. Again, the warmup shift will always be down. Run the radio with the covers on in a tightly packed rack and the numbers will be higher. Run it will all the covers off and six fans, the numbers might be lower.

On most of the bands things aren't quite so simple. You have some crystals converting bands up, and others converting them back down again. The drift you see will be the delta between the various oscillators. Different bands will have different drift. 

Not so simple ….

Bob

On Jun 1, 2013, at 9:04 AM, ToddRoberts2001 at aol.com wrote:

> In the past I have determined that most of the
> initial warm-up drift comes from the main VFO tube V701.
> The initial turn-on drift might be several hundred Hz
> or nearly zero in the first ten minutes. The other
> oscillators are all crystal controlled so their turn-on drift
> is fairly low.
> 
> I found that by swapping several different 6BA6 tubes for V701
> I would usually hit on a "good" tube that had nearly zero 
> drift from a cold start. Worth trying if you have several
> spare 6BA6 tubes available.
> 
> There may still be some small long-term drift while the 
> receiver stabilizes thermally but the main drift seems most 
> noticeable in the first ten minutes from a cold start and seems 
> mainly due to the V701 warm-up characteristics.
> 
> 73 - Todd WD4NGG
> 
> 
> In a message dated 5/31/2013 12:28:08 A.M. Eastern Daylight Time,  
> gordon at n6wk.com writes:
> 
> Since I am fairly new to my R-390A, I have a question.
> How long does it  normally take from cold turn on, until the Radio is 
> stable and no longer  drifts?
> 10 minutes, 30 Minutes, an hour ?
> What is considered normal and  how much can I expect it to drift during 
> that  time?
> Thanks,
> Gordon
> N6WK
> 
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