Stability and oscillators

WHAT IS AN OSCILLATOR?
Oscillators are used in radio circuits to produce radio and audio frequency energy,
generally with a sinewave output, though the waveform can be many shapes such as a
square wave or saw tooth. The sinusoidal waveform may be AC or DC. Oscillators used
in radio frequency circuits are always very low power devices, in contrast to AC generators
in a power station. Nevertheless, the AC power generator and the electronic oscillator are
related, in that they both produce sinusoidal electrical energy. Unlike the AC generator
though, the electronic oscillator can produce output on frequencies measured in tens of
megahertz. Special oscillators can produce output at microwave frequencies.
An oscillator producing a radio frequency output is actually a low power transmitter in its
most basic form. In an actual radio transmitter and receiver, up to several or more
oscillators may be employed.
We are going to look a number of different types of oscillators and their circuits in this
reading. Don t be put off by the number of circuits as you don’t have to remember them in
detail.
You do need to learn the identifying features of each oscillator circuit
. In the exam
you will be asked to name the type of oscillator shown in the circuit. The fundamental
principles of oscillator operation will be explained for each of the types. You will find a
repeating theme across all of the oscillator types.