[time-nuts] Re: pulling some crystals

[glen english LIST]

Hi Bob

thanks for the comment. I had similar problems with 3OT, also, which I 
got a bunch made of by Kystally. They were quite good but pulling for 
10-15 years seems difficult.

 Â I'll read up on pre aging them a bit more, maybe the aging I see can 
be  reduced. and talk to the mfr. The inductor I used needs a tweak I 
find, but its also a bit hard to know precisely, because the xtals I 
have have not aged yet- IE I'm just pulling them off their original cal 
frequency.

Either a 16 to 24 MHz fundamental crystal multiplied up, or the OT 
crystal easily meet my phase noise objectives. Using a 16 or 24 meg 
fundamental crystalk, pulling the hell out of that is fine.....Although 
at the extremes, I can detect some frequency tuning hysteresis and lack 
of mototonicity so there are limits. and a lack of monotonicity will 
drive a loop crazy.

-glen


On 7/12/2023 1:40 pm, Bob kb8tq wrote:
> 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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