In a radio receiver, a bandspread control is a secondary tuning control that allows accurate tuning of closely spaced frequencies of a radio band.
One method of adding a bandspread control was to put a relatively small value variable tuning capacitor and dial directly in parallel with the main tuning variable capacitor ( or connected to a tap on the coil of the tuned circuit).
[2] A second method, mechanical bandspread, was a second tuning knob connected through a gear train to the main tuning knob; each turn of the bandspread dial moved the main dial through a small part of its range, improving the precision of tuning.
With the advent of digital frequency synthesizers that could be set with high resolution by a keypad or incremental tuning knob, the requirement for bandspread control in many applications was eliminated.
In the mid-1960s, some British portable radios[4] had a separate 'Bandspread' waveband covering the highest frequencies of the medium wave (AM) band (typically 1400 – 1600 kHz) to simplify tuning of popular commercial stations such as the offshore Radio Caroline and the continental Radio Luxembourg.