Use of multivibrators in small telemetry systems

In many small telemetry systems it is convenient to use information derived from a transducer to modulate the period of a multivibrator, the multivibrator waveform being used in turn to modulate a radio or line link. In this way, the measurement is easily made in digital form, and errors due to nonlinearity of the carrier modulator are removed. The use of multivibrators in this application is considered, and accurate equations are derived for the period of a conventional collector-coupled multivibrator and for the period of a multivibrator, using constant-current charging of the coupling capacitors. The mechanisms of variation of the period with varying ambient temperature are discussed, and the temperature stability is determined. The use of the two timing periods of a multivibrator as a double-channel system is considered, and a method is given which reduces crosstalk between the two channels to a negligible amount.