[time-nuts] Re: pulling some crystals

[john.haine at haine-online.net]

Might be easier to add an extra stage of frequency division and use a lower frequency non-overtone crystal?  There was a neat little circuit invented years ago by Racal that gave a way to digitally insert very small frequency increments, I believe to permit "digital pulling" of a reference oscillator.

-----Original Message-----
From: Bob kb8tq via time-nuts <time-nuts at lists.febo.com> 
Sent: Thursday, December 7, 2023 2:40 AM
To: glenlist at cortexrf.com.au; Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Cc: Bob kb8tq <kb8tq at n1k.org>
Subject: [time-nuts] Re: pulling some crystals

Hi

The simple answer is that a wide pull ( = enough to cover 10 years aging)  5th overtone is a bit of a complicated design. It can be done, but the circuits (and the designs behind them) are all a bit obscure / insane. 

I’d suggest that a 3rd overtone 98.304 might be another choice.

Bob

> On Dec 4, 2023, at 9:42 PM, glen english LIST via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 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:
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