This is a simple circuit that is can generates narrow pulses at about 700-800Hz frequency. The pulses, containing harmonics up to the MHz region, can be injected into audio or radio-frequency stages of amplifiers, receivers and the like for testing purposes. This is the figure of the circuit;
This circuit is work if Q1 & Q2 form a complementary astable multivibrator, whose operating frequency is set mainly by R3, C2 & C3 values. Output pulses are taken at Q2 Collector and applied to the probe by means of decoupling capacitor C1. D1 provides a symmetrical shape for the output waveform. If an earclip or headphone jack is plugged into J1, the connection from Q2 Collector and C1-C2 is broken by the switch incorporated into J1: in this case the circuit becomes a two-stage amplifier.
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