This paper describes the digital part of a simplex binary telemetry system for conveying control signals to some remote body such as a missile. The decoder in the remote body is small, light, has a low power consumption, and is designed to operate above a certain noise threshold. When the signal-to-noise ratio of the signal at the input to the decoder is low the latter only accepts information which has a high probability of being correct thereby causing the rejection of most of the transmitted information. When information is rejected the remote body functions on the data which were last accepted by the decoder.Both experimental and theoretical results are presented for error rate and received frame rate, and the effect of asymmetry in the binary channel is examined.