[time-nuts] Old Crystal oven lying around

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Nov 17 23:15:50 EST 2006


Magnus Danielson wrote:
> Hi!
>
> I have a HP G-69B-2 Z-235 Crystal Oven 100 kHz lying around. I'm considering
> heating it up and run it (just for fun). Operating temperature is 65 C.
>
> Anyone care to share any information on this device? I have no clue which box
> it ever was in or anything. Also, thoughts of suitable oscillator setups?
>
> I should probably have a run-by the network analyzer.
>
> Cheers,
> Magnus
>
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>   
Magnus

Typical face shear 100kHz crystals have a maximum drive level of 2 
milliwatts and a max ESR of 5kohms.
This implies a maximum crystal drive current of 630uA rms.
You may wish to restrict the crystal dissipation to less than 100uW or 
less corresponding to a crystal current of 140uA rms or less for a 
crystal ESR of 5kohm.

At such low frequencies an opamp with a shunt feedback resistor becomes 
a viable option for the buffer amplifier.
Just connect the one end of the crystal directly to the opamp summing 
junction.
If an OPA134 opamp with a 140 uA crystal current and a 14K shunt 
feedback resistor were employed to drive 2V rms into a 1K load the 
distortion products will be 80dB below the carrier and the output will 
have relatively low phase noise. An additional buffer stage is required 
to drive a 50 ohm load.

Bruce




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