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

[k6jek]

Well shucks.  I got a bit of a handle on the drift and the thing hops on me.  It just doesn't want to be pinned down.

Thanks everyone

Jon

On Aug 31, 2011, at 6:44 AM, <kirklandb at sympatico.ca> <kirklandb at sympatico.ca> wrote:

> 
> 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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