[time-nuts] pulling oscillators

[Don Latham]

The crystal oscillators are reference oscillators in 2 meter ham radios. I
wanted to make the least perturbation in the radio, hence pulling instead
of simply introducing the correct reference. I will be using a reference
of the nominal frequency the radio should have, so really should not need
to pull more than a few ppm if that? also not woried about the phase
noise, either. Will derive the driving signal from my gps 10 mhz or from
one of my FEI Rb devices. I need the accurate frequencies, or at least I
think I do, because the 2 meter radio will drive a transverter to 2.4 GHz
moonbounce.
Sorry about not knowing how far I need to pull, or the specs of what's
there. I suspect there has been some drift since the radio was made.
Putting in a vcxo or varactor simply puts off the problem, as then I have
to monitor <that> frequency and control it. I could cobble in a little
tuning cap, but still would be left with a pretty temp sensitive
reference.
Hope the question is clearer, and thanks to all who replied!
Don

Adrian
> Don,
>
> if you have a reference oscillator of the right frequency, what's the
> the purpose of trying to pull a CMOS oscillator to the same frequency,
> rather than just using the reference frequency?
> Please be more specific on whant your requirements are.
>
> Adrian
>
> Don Latham schrieb:
>> Hello all:
>> I've developed a need for pulling crystal oscillators built in to pll
>> circuits. These are cmos, and have the common style oscillator circuit
>> built in. The crystal is across an inverter in the chip, and there is a
>> small cap between each end of the crystal and ground.
>> The chips are pll's in radio transceivers, early at that.
>> I could carefully remove the crystals and caps, simply driving the
>> non-inverting input on the chip with the reference, but I would rather
>> simply tack on a very small cap and "pull" the crystal oscillator with
>> an
>> external reference signal of the right frequency.
>> Anyone out there tried this?
>> Thanks
>> Don
>>
>>
>>
>>
>
>
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-- 
"Neither the voice of authority nor the weight of reason and argument are
as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
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www.lightningforensics.com
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