Oscillator Drift and Frequency Stability

Oscillator drift can be associated directly to frequency stability

. Drift is the unwanted change in frequency measured over seconds, minutes or hours.

In the world of electrical engineering and specifically in telecommunications, frequency drift is an unplanned and uniformed offset of an oscillator from its nominal frequency. It happens due to change in temperature, which alert the piezoelectric effect in a quartz crystal or due to the voltage regulator problem which is responsible for the bias voltage to the oscillator.

I guess you might have experienced on a radio transmitter, frequency drift can cause a radio station to drift into an adjacent channel, causing illegal interference. Due to this, there are typically regulations specifying what type of tolerance such oscillator must have. A temperature compensated voltage controlled oscillator is used for FM.

On the receiver side, frequency drift was mainly a problem in early tuners, mainly for analog and dial tuning, and especially on FM, which exhibits a capture effect. However, the phase locked loop essentially eliminates the drift issue. For transmitters, a numerically controlled oscillator also does not have problems with drift.

It is different from Doppler shift, which is a perceived difference in frequency, even though the source is still producing the same wavelength, because the source is moving. It also differs from frequency deviation, which is the natural and necessary result of modulation in both FM and phase modulation.

Sources of oscillator drift:

Thermal instability causing oscillator drift

Thermal instability of inductors

Suggested cures for oscillator drift are underneath:

Use quality components for the application

Use the best inductor possible

Use the best regulated power supply at the lowest voltage possible

Make sure your oscillator is "well buffered" to minimize oscillator drift

Mechanical stability has an effect on oscillator drift

Shielding and heat sinking

Oscillator Drift and Frequency Stability

By: Fox Online

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