An oscillator for testing the linearity of s.s.b. transmitters and/or linear amplifiers.
150Hz was included for convenience as it is the frequency of the squelch tone in military radios. It is also used to enable re-broadcast (the military equivalent of a repeater).
2079Hz is the modulation frequency which will produce the first carrier drop-out of an f.m. transmitter when the peak deviation is 5kHz; i.e. a modulation index of 2.4.
Both oscillators use the Wien bridge circuit with thermistor (R53) amplitude stabilisation. These are no longer manufactured.
A satisfactory alternative is a f.e.t. In some applications this is an advantage because the amplitude settles much more rapidly than it does with a thermistor (or an incandescent bulb). See the last picture for an example.
