Reed receiver
A reed receiver or tuned reed receiver (US) was a form of multi-channel signal decoder used for early radio control systems. It uses a simple electromechanical device or 'resonant reed' to demodulate the signal, in effect a receive-only modem. The encoding used is a simple form of frequency-shift keying. These decoders appeared in the 1950s and were used into the early 1970s. Early transistor systems were in use in parallel to them, but they were finally displaced by the appearance of affordable digital proportional systems, based on early integrated circuits. These had the advantage of proportional control. (Wikipedia).
