Reed receiver

It uses a simple electromechanical device or 'resonant reed' to demodulate the signal, in effect a receive-only modem.

These allow a high current load to be controlled, such as the model's propulsion motor.

Each reed forms an independent channel and they may be activated individually or in combination, depending on the signal from the transmitter.

[note 3] The number of distinct frequencies usable within this range depends on the selectivity or Q factor of each reed.

Twelve reed systems were known, but were only required for large ship models, typically warships, with many channels for triggering "working features" such as turrets and cannon firing.

It is sometimes incorrectly claimed that the origin of the resonant reed decoder was in the wartime torpedo-control patent granted to the actress Hedy Lamarr.

A minor aspect of the radio control system described does use a similar frequency-keying mechanism to select left and right rudder, also this is done by separate filters, presumably electronic rather than reed, of 50 & 100 Hz.

Most had a single oscillator, that generated different tones as control buttons were pressed one-by-one.

Many period transmitters merely used a number of push-button switches on their case, although some combined these into joystick or wheel controls.

By visually monitoring the vibrating reeds, the pilot could determine their position within the radio beams, and thus over the ground.

This gives a more selective mechanical filter, allowing more frequencies to be spaced closely together.