You're probably thinking of the oscillator that Marv Frerking
called a "grounded-base oscillator". I have seen it called other
names as well. Basically, what you do is first build an LC
(ie no xtal) Colpitts oscillator and tune it to the crystal frequency
you want to eventually use. Then insert a resistor of a few
dozen ohms in series with the emitter. Now, readjust the feedback
capacitors on the oscillator to get it to oscillate OK with the resistor.
Finally, replace the resistor with a series resonant crystal.
It will be forced to oscillate at the frequency of the original LC
oscillator, since there is no gain anywhere else. Thus you can
design for either the fundamental or a specific harmonic and like
you say it can't flip to a different overtone. For more details,
read one of Frerking's books.

Rick N6RK

"Paul Burridge" wrote in message
news

Hi,

I'm trying to track down the name for a certain type of oscillator
which I dimly recall seeing in an old book called Radio & Line
Transmission that I bought and lost over 3 decades ago.
In simple terms, it has a crystal in the base/emitter circuit and a
C/L tank for the resonant frequency of the crystal in the collector
circuit. In this way it can't flip into an overtone since it only has
gain at the crystal's fundamental. Anyone know the name for it?

Thanks,

p.

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