[time-nuts] pulling some crystals

[glen english LIST]

After some commentary, please:

I built some 98.304 MHz 5th overtone oscillators, the crystals have a 60 
deg C turning point, they're kept close to that temp and varactors  pull 
it around.

It's a reference for a  UHF PLL. However I am having difficulty with a 
well reproducable production configuration and pulling. Pulling too much 
and I see spurious modes.

I've now considered driving temperature on the crystal  to pull it 
around also , and back off the amount of varactor pull. IE a hybrid of 
the two approaches.

I've considered now going back to 49.152 reference  and using a 16.384 
fundamental crystal  in an harmonic oscillator configuration (x3) , or a 
tripler, which results in a bit of subharmonic contribution- not really 
desirable but I could put an idler/diplexor on that and then kill the 
subharmonic component.

  or using a 3rd overtone 49.152 crystal.  I never had problems with the 
spurious modes in the old days wildly pulling 3rd overtone 35 meg xtals.

The pulling requirement needs to cover it for 10 years of aging. 
Presumably I can ask the crystal mfr to put more years on it to reduce 
aging.

Comments please ?

with many thanks - glen.

On 29/11/2023 2:48 am, Joe Dempster via time-nuts wrote: