[R-390] R-390 zero adjust problem fixed and have more questions.

[Tim Shoppa]

Mark wrote:
> Then run through the bands, monitoring how far off each 
> crystal frequency is. The results may surprise you. Crystals not only 
> drift with temperature, they age 2 to 5 ppm per year, and temperature 
> accelerates this. After fifty years, drift would be about 4250 Hz on a 
> 17 Mc crystal.

My experience is that the 17Mc crystal drifts far more than the
ones in the bandswitch. A good chunk to a few kc is typical
of the 17Mc in the 0-8Mc converter, while the band-to-band
difference on my rigs (keeping within 0-7 and 8-32) is just
a few hundred Hz.

> Since heat accelerates this process, and the crystals are 
> in an oven, you can expect more. Maybe more than 8 kHz.

I haven't seen that much! Heated crystals in OCXO tend to show
a bake-out time, during bake-out they will drift a good amount but
after bake-out they're fairly flat. But those are very well sealed
OCXO cans, I think the 17Mc crystal is less hermetically sealed and
perhaps foreign contaniments prevent the "flattenning out" from
occuring.

Tim.