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squegging

Squegging

Stan Zurek, Squegging, Encyclopedia-Magnetica.com, {accessed on 2020-03-28}
reviewed by Jeff Jones, 2014-09-03
Typical waveform of automatically starting and stopping squegging oscillations

by S. Zurek, E. Magnetica, CC-BY-3.0

Squegging - a phenomenon occurring in an oscillator, in which one or more oscillations stop for a certain time interval and then restart automatically, so that the operation is intermittent but repeatable, even for indefinitely long time. 1) 2)

Circuits which show this type of behaviour can be referred to as: squegging oscillator, squegger, self-quenching oscillator, or blocking oscillator.3)

Operating principle

Squegging was discovered as an unwanted effect. In 1920's it was called “motorboating” because of the sound it produced with vacuum tube audio amplifiers.4)

Such unwanted effects can happen for modern RF circuits due to parasitic parameters of a given circuit. Therefore, in most cases squegging is a phenomenon to be avoided.

An example of an electronic circuit (based on Hartley oscillator) behaving as a squegging oscillator

by S. Zurek, E. Magnetica, CC-BY-3.0

The effect occurs for instance because a DC bias shifts the operating point of a transistor into saturation which causes the oscillations to cease periodically.5) The bias then slowly reduces in the absence of oscillations, which can eventually resume, and the whole cycle restarts.

Close up of a single burst of squegging oscillations

by S. Zurek, E. Magnetica, CC-BY-3.0

In a non-linear oscillator the most likely condition for squegging is if the Q value of the resonator is low and if the starting gain of the amplifier is much larger than necessary to ensure that oscillations occur. 6)

For the example electronic circuit shown in the image, squegging occurs only for fairly narrow set of parameters. For instance, it is enough to change the transistor to a different model, e.g. 2N2222 instead of 2N2369 for the oscillations to be continuous (i.e. without squegging).

However, the effect can be also used as a desirable feature. The character of oscillations can be used for instance for identification purposes7) or for RF communication as a super-regenerative oscillator.8)

References

squegging.txt · Last modified: 2019/06/03 18:30 (external edit)

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