Virtually any audio oscillator can be used to drive the burst generator, with the proviso that it must be capable of 1V peak to peak output level. Distortion is not important as long as it is within reasonable limits (less than 1% is to be preferred).
The 4035 shift register is clocked by the incoming waveform, and the outputs drive the CMOS analogue switch controls. The entire circuit is normally inhibited by the repetition generator circuit, which is a simple timer. When the hold-off time expires, the next incoming signal zero crossing will start the cycle, allowing 10 half cycles to pass before switching off again. This sequence continues as long as the unit has an applied input signal.
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