Oscillators generate the frequencies used in radio and electronic equipment. The performance of those which determine the operating frequencies of radio systems is tremendously important. Most oscillators must:
• Generate a precise frequency of high purity.
• Be highly stable, i.e. produce an output constant in frequency and level despite changes in temperature, supply voltage and load.
• Be tunable in frequency.
• Produce minimum noise and microphony (fluctuations in frequency with vibration).
These requirements conflict. A readily tunable oscillator cannot be precise and highly stable, and compromises must be made; either a less stringent specification must be accepted where permissible or the facility for tuning restricted.
Not all oscillators need to produce a pure output, devoid of spurious frequencies. The clock generators in digital circuitry, for instance, produce square waves, but a radio transmitter carrier generator and receiver local oscillator must produce a pure sine wave output if spurious radiations and receiver responses are to be avoided.