Editing Tuned radio frequency receiver (section)

{{Refimprove|date=April 2013}}
[[Image:1920s TRF radio manufactured by Signal.jpg|thumb|upright=1.2|This 1920s TRF radio manufactured by Signal is constructed on a [[breadboard]] ]]
[[Image:Tuning Neutrodyne receiver 1924.jpg|thumb|upright=1.2|Tuning a TRF receiver, like this 5 tube Neutrodyne set from 1924 with two stages of RF amplification, was a complicated process. The three tuned circuits, controlled by the 3 large knobs, had to be tuned in unison to the new station. So tuning in a station was a process of successive approximation. Once a station was found, the numbers on the dials were written down, so it could be found again.]] 
[[Image:Tuning a TRF radio 1925.jpg|thumb|upright=1.2|Tuning all 3 stages of a TRF set in unison. This 1925 Grebe Synchrophase receiver has [[thumbwheel]]s instead of knobs which can be turned with a finger, so a third hand is not needed. ]]

A '''tuned radio frequency receiver''' (or '''TRF receiver''') is a type of [[radio receiver]] that is composed of one or more tuned radio frequency (RF) [[amplifier]] stages followed by a [[detector (radio)|detector]] ([[demodulator]]) circuit to extract the [[audio signal]] and usually an audio frequency amplifier. This type of receiver was popular in the 1920s. Early examples could be tedious to operate because when tuning in a station each stage had to be individually adjusted to the station's [[frequency]], but later models had ganged tuning, the tuning mechanisms of all stages being linked together, and operated by just one control knob. By the mid 1930s, it was replaced by the [[superheterodyne receiver]] patented by [[Edwin Howard Armstrong|Edwin Armstrong]].