multiple crystal pierce oscillator

[frank]

Hello,


I was wondering if it was possible for the same pierce oscillator to
operate with 2 crystals. Obviously only 1 crystal will be turned on
for a time (with the aid of half transmission gates). The objective is
to create an oscillator capable of oscillating at 2 different
frequencies (TX and RX) without the need of 2 oscillators. Is this
possible ? what would be problems to expect ?


Frank

 

[mikem]

Crystal-controlled radio scanners (eg Regency, RatShack) of yore had a
bank of up to 16 crystals where a 1:8 or 1:16 TTL open-collector
decoder chip was used to ground one of the crystals at a time. The
other end of all of all the crystals was tied to the base of
transistor which formed a pierce oscillator.

Since the IF of the receiver was constant (usually 10.7Mhz), then as
each crystal in turn was switched into the oscillator, the receiver
momentarily listened on each channel in turn, stopping to listen only
if that channel has activity. Your version of this only has two
different frequency crystals, separated by your IF.

MikeM