A Multichannel PAM-FM Radio Telemetering System

A multichannel time-division system of the PAM-FM type is described. It can provide as many as 64 channels with an information bandwidth per channel greater than 800 cps or fewer channels with a corresponding increase in the information bandwidth per channel. Modulation and multiplexing in the airborne equipment, and demultiplexing in the ground station, are performed by simple pentode gating circuits which derive their gating signals from crystal-resistor matrices. Transmission of dc signals over the radio-frequency link is avoided by a process of double modulation. The novel technique of reactance switching provides a simple FM transmitter with wide linear frequency deviation. The airborne portion of the system is miniaturized through the use of potted unit construction. In each channel, the over-all linearity is better than ±1 per cent, the cross talk is less than 1 per cent, and the signal-to-noise ratio is greater than 55 db.