Tuesday, 15 February 2011

crystal oscillator

 

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The crystal oscillator depicted at Figure is a typical example of an RF or radio frequency crystal oscillators which may be used for exciters or RF converters. Transistor Q1, can be any transistor which will operate up to 150 MHz, such as a 2N2222A. The turns ratio on the tuned circuit depicts an anticipated nominal load of 50 ohms. This allows a theoretical 2.5k ohms on the collector, so typically a 7:1 turns ratio for T1 would be used. Use the: L * C = 25330 / F02 formula for determining L and C in the tuned circuits of crystal oscillator. Personally I would make L a reactance of around 250 ohms. In this case, I’d make C1 a smaller trimmer capacitor. The crystal at X1 could be an overtone type crystal for the crystal, selecting a L * C for the odd particular multiple of overtone wanted in your crystal oscillators. Typically the output of the crystal oscillator would be followed by a buffer circuit. A pictorial diagram of the crystal controlled oscillator circuit is shown in Figure 2-7. Note that the components in this diagram are illustrated as component blocks as they might actually look placed on the circuit, rather than as electronic symbols in a circuitdiagram or schematic.

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