Elimination of noise in telemetry systems by pulse-width discriminator

Abstract

A pulse-width-discriminator circuit (PWD) was developed and applied for noise reduction in an FM pulse-interval-ratio modulation telemetry system. The PWD was incorporated as an intermediary between the tuner and the demodulator. The application of the circuit as a noise filter is a result of its ability to distinguish between pulses of different durations and its ability to eliminate pulses whose durations are less than some predetermined value. Since spikes of radio-frequency interference (RFI) occurring at the tuner output were of significantly shorter duration than the encoding pulses, they were virtually eliminated by the PWD. This prevented false triggering of the demodulator and resulted in a noise-free final demodulated output signal. This system was tested during telemetered blood pressure measurements in an unrestrained dog and proved to be extremely effective in eliminating spurious noise caused by electromagnetic interference in the radio-frequency range.