[Central-Electronics] 20A drift, breaking my heart.

[kirklandb at sympatico.ca]

I've been working on a modern project and yes crystals can jump in frequency. These days we are using 19.2 MHz crystals as reference oscillators 
for 800, 1900 MHz equipment. Small jumps in xo frequency cause larger jumps in the final frequency. Talking to XO manufacturers, there are many reasons.
Some are due to contaminates on the crystal. If the drive level changes/fluctuates, then the magnitude of the xo osc changes and can shift a contaminant particle
 there by causing an xo freq jump. Another effect is due to how the crystal blank is mounted, ie. if it is rubbing against something.  
 There are other mechanisms inside the structure of the crystal as well.  Crystals also exhibit hysteresis effects over temperature as well.

I am not saying that any of these are causing your drift/jumps. Just answering the question "Can they do that?"


> ________________________________
> From: k6jek <k6jek at comcast.net>
> To: central-electronics at mailman.qth.net
> Sent: Tuesday, August 30, 2011 10:29 PM
> Subject: [Central-Electronics] 20A drift, breaking my heart.
> 
> I was happy for awhile but my hopes were dashed.  This old 20A was drifting a lot, still drifting about 26 Hz every 10 minutes after an hour.  I took it out of the case and propped the chassis up so air could flow underneath.  Voila! It got darned stable. After an hour drift was only 1 Hz in 10 minutes.  Drift after 30 minutecs was only 5 Hz/ten minutes. How about that?
> 
> Would just a little air make it  better?  I put the 20A back in the cabinet and put the most insignificant of fans on the outside on the left pointing into the lower left cabinet vent, a 4" 240V fan running on 120.  It worked much better than I expected.  Drift was down to about 3 Hz every 10 minutes after an hour.
> 
> Then tonight, while participating in the vintage SSB net it hopped, jumped  60 Hz.  What the heck? 
> 
> Normally I'd think this was a faulty cap, one that has a temperature sensitive fault.  But you know those caps surrounding the crystal in the 20A, C86, 87 and 88?  This early model has none of them.
> 
> Is it the crystal itself?  Can they do that?
> 
> Thanks,
> 
> Jon 
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