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Quartz Crystals

Harmonic Crystal Oscillator

This circuit is ideal when a crystal must be made to resonate on its fundamental or any specific odd harmonic. It is therefore very usefull for VHF receivers and crystal markers. Crystals above about become 20MHz too fragile so higher frequency crystals will normally use harmonics. Choose the correct harmonic by selecting the tuned circuit.






Also shown is the same oscillator with a frequency multiplier. A typical crystal would be cut to 15MHz but designed and marked for operation on its 3rd harmonic - 45MHz. The multiplier stage multiplies the frequency to 135MHz to create a local oscillator for 145.700MHz. The second drawing above demonstrates how a 3rd harmonic 24.1667MHz crystal may be used to generate a signal on 145.000MHz.


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