CRYSTAL OSCILLATOR PROVIDES LOW NOISE.

Conventional crystal oscillators, despite the high Q of the crystal, are still very noisy, and produce many spurious signals mainly because of the large-signal characteristics of the transistor in the circuit. An inproved circuit design is presented in which the crystal, in addition to determining the oscillator's frequency, is used also as a low-pass filter for the unwanted harmonics and as a bandpass filter for the sideband noise. The circuit arrangement provides two significant advantages. First, the noise bandwidth is limited to less than 100 Hz. And, second, all higher harmonics are substantially suppressed - 60-db down for the third harmonic of the 4-MHz fundamental oscillator frequency.