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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 31st Oct 2019, 10:38 pm   #1
kkyahoo
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Default Microwave Modules 70cms to 28MHz converter

Does anyone know the spec of the 101 MHz xtal
in the 70cms to 28MHz converter?

Kevin
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Old 1st Nov 2019, 9:38 am   #2
Steve G4WCS
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Default Re: Microwave Modules 70cms to 28MHz converter

theres a manual for the transverter here.

http://oz1bxm.dk/manuals/MicrowaveMo...ter-432-28.pdf

They are usually 20 or 30pf capacitance but you’d need to know whether its a fundamental or 3rd overtone
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Old 1st Nov 2019, 11:09 am   #3
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Default Re: Microwave Modules 70cms to 28MHz converter

That's an interesting oscillator. THough the crystal appears to be in parallel across the transistor base to ground, the transistor is actually used as a common base amplifier and the crystal works as a bizarre narrow-band decoupling capacitor for the base. So it is a series-mode crystal. It will be either third or more probably 5th overtone mode. Either will do.

As far as loading capacitance goes, there isn't any. You want true unloaded series mode to get the frequency dead accurate. It won't be badly off at other load values.

Overtone crystals are devils to pull or adjust. Pullability (parts per million) scales down by the square of the overtone number.

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Old 2nd Nov 2019, 2:17 pm   #4
kkyahoo
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Default Re: Microwave Modules 70cms to 28MHz converter

I think it's 5th overtone, series resonant.

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