Crystal oscillator provides low noise

The oscillator delivers an output of high spectral purity without any substantial sacrifice of the usual stability of a crystal oscillator. 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.
Crystal oscillator provides low noise - schematic

The noise bandwidth is limited to less than 100 Hz. All higher harmonics are substantially suppressed—60 dB down for the third harmonic of the 4-MHz fundamental oscillator frequency.

Recommended videos

  • Electronics: Introduction to LC Oscillators circa 1974 US Air Force Training Film
    Duration: 19:55.
  • Electronic Basics #17: Oscillators || RC, LC, Crystal
    Duration: 6:02.
  • Crystals Go to War 1943 Reeves Sound Laboratories; Piezoelectric Quartz Crystals for Radio
    Duration: 41:25.