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please help oscillator

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matbymay

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this oscillator dosent work. i have put image below .
i implemented with pcb and soldered it.
but still giving unstable values
any idea or do you have any good one (20 mhz or more)

thank you
 

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MikeMl

Well-Known Member
Most Helpful Member
Does it not start reliably, or is it drifting?

Does it oscillate at approximately 1/3 of 20Mhz?

20Mhz crystals are usually third-over tone type, meaning that the crystal has to be forced to oscillate on its overtone, while it prefers to oscillate on its fundamental freq, which would be about 6.6MHz for this crystal. Overtone oscillators must have an LC tuned circuit in them to force the crystal to oscillate on its overtone...

I think you will find that in your circuit, the crystal will be oscillating at its fundamental.

Read this:
 

Diver300

Well-Known Member
Most Helpful Member
Does it not start reliably, or is it drifting?

Does it oscillate at approximately 1/3 of 20Mhz?

20Mhz crystals are usually third-over tone type, meaning that the crystal has to be forced to oscillate on its overtone, while it prefers to oscillate on its fundamental freq, which would be about 6.6MHz for this crystal. Overtone oscillators must have an LC tuned circuit in them to force the crystal to oscillate on its overtone...

I think you will find that in your circuit, the crystal will be oscillating at its fundamental.
20 MHz crystals are usually fundamental. The change-over to overtone is nearer 30 MHz nowadays.
 
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