System design criteria for space television

A narrow band television system for relaying to earth images of the planets is described. The principal consideration is the necessity of communicating over extremely long ranges. Because of the resulting high noise environment, the channel bandwidth is severely restricted. Bandwidth compression is achieved by storing the video signal on magnetic tape or photographic film and transmitting at a reduced information rate. An f.m.-p.m. telemetry system is utilized. The doppler-shifted carrier is recovered from the noise by a very narrow tracking filter or phase-locked loop. The derived carrier is mixed with the incoming signal to yield the noisy video information. The discriminator is also a phase-locked loop with sufficient bandwidth to track the information signal. The recording operation is reversed at the receiver to present the video image at periodic intervals, or a facsimile technique may be employed. The main interest of the paper is directed toward the theory and design of the very narrow band telemetry system and the unconventional discriminator required for ultra-long-range television communication.