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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.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 fed 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. Consumer multistage TRF radios suffered from poor selectivity and required several tuning knobs in a row. [[File:twostagetrfreceiver.png]]<BR>''Two Stage TRF Receiver''Crystodyne was not introduced as an alternative to superheterodyne, but rather an alternative to the vacuum tube being used in a radio design. The crystal radio operated without the vacuum tune, using a solid state crystal which has led to the innovation of the transistor which eventually replaced vacuum tunes in radios.It is sometimes mistakenly stated that Software Defined Radio is something different from the superheterodyne receiver design. This is not true. Today's SDRs still use superheterodyne. This is due to the consistent performance a superheterodyne receiver offers across a large range of frequencies while maintaining good sensitivity and selectivity.It is sometimes mistakenly stated that Software Defined Radio is something different from the superheterodyne receiver design or does not require superheterodyning. This is not true. Today's SDRs still use superheterodyne. This is due to the consistent performance a superheterodyne receiver offers across a large range of frequencies while maintaining good sensitivity and selectivity.Modern SDR receivers are using variations in traditional superheterodyne. They do not "sample" the antenna directly. Despite some appeal, the data converters are not directly on the antenna. It is simply not practical to do it this way. An analog front-end remains necessary before the ADC in the receive path and after the DAC in the transmit path that does the appropriate frequency translation, this is where superheterdyning is being used.Modern SDR receivers are using variations in traditional superheterodyne. They do not "sample" the antenna directly. Despite some appeal, the data converters are not directly on the antenna. It is simply not practical to do it this way. An analog front-end remains necessary before the ADC (Analog to Digital Converter) in the receive path and after the DAC (Digital to Analog Converter) in the transmit path that does the appropriate frequency translation, this is where superheterdyning is being used.