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== Alternatives ==Before radios implemented the superheterodyne design most of the available radios on the market were Tuned Radio Frequency (TRF) receivers. In an early TRF receiver there were tuned circuits separated by the radio frequency (RF) amplifier stages and the last tuned circuit feeded the AM detector stage. The individual tuning capacitors were attached to separate tuning dials. Each had to be reset each time a different station was selected.