Delay line controlled subcarrier discriminator

A new FM subcarrier discriminator which utilizes a delay line as the frequency stable element has been developed at the Naval Research Laboratory. When the equipment is used as a telemetering discriminator under field conditions, linearities within 0.25% of full scale can be readily obtained. Theoretically, the linearity is perfect and linearities within 0.1% can be obtained under controlled conditions. No “screwdriver” or tuning adjustments are necessary with the exception of a zero balance in the output voltmeter circuit because the output has been made essentially independent of tube characteristics and component tolerances by the utilization of low power pulse techniques in conjunction with clamping and gating circuitry. The sensitivity is determined by the delay line in combination with a regulated reference voltage.