Is it possible to toggle between two precise crystal frequencies? Also, one of the frequencies is very rare and it is hard to get the crystal. Is it possible to use some sort of variable crystal oscillator whos frequency could be set with componants? the two frequencies are 17.743472mhz and 14.31818mhz.

 

Nevermind. Misunderstood the question.

 

It's dead easy to switch crystals, either directly switch the crystals, or use separate oscillators and switch them. For examples, check any of the old 145MHz crystal based transmitters.

For your obscure frequencies, simply have them made for you, it's a common requirement and crystal manufacturers offer a 'made to measure' service.

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Probably best to have two oscillators, each of which can be trimmed to frequency. Switching between them can be done by switching power to them. If rapid switching is desired, then leave them both running and multiplex the outputs using a 2:1 mux.

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Mike ML.