Tuned Radio Frequency Receiver

A tuned radio frequency receiver (or TRF receiver) is a type of  radio  radio receiver that receiver that is composed of one or more tuned radio frequency (RF) amplier (RF) amplier stages followed by a detector a detector (demodulator) demodulator) circuit to extract the audio the audio signal and signal and usually an audio frequency amplier amplier This type of receiver was popular in the !"#$s %arly examples could be tedious to operate because when tuning in a sta&on each stage had to be individually ad'usted to the sta&ons frequency sta&ons frequency but  but later models had ganged tuning the tuning mechanisms of all stages being lin*ed together together and operated by 'ust one control *nob +y the mid, !"-$s it was replaced by the superheterodyne receiver patented by %dwin Armstrong Armstrong Block diagram

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TRF receiver includes an RF stage o A detector stage o o And an audio stage Two or three RF ampliers are required to lter and amplify the received signal to a level su.cient to drive the detector stage RF sec&on o /sed to detect the signal o +andlimit the received RF signal And amplifying the received RF signal o A0 detector 1emodulates the A0 wave and converts it to the original informa&on signal o Audio sec&on /sed to amplify the recovered signal o

A12A3TA4%56 TRF receivers are simple to design and allow the broadcast frequency 7-789: to o !;<$89= 9igh sensi&vity o 1>5A12A3TA4%56

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At the higher frequency it produces di.culty in design >t has poor audio quality 1rawbac*s >nstability   1ue to high frequency mul& stage ampliers are suscep&ble to brea*ing into oscilla&on  As gain of RF amplier is very high a small feedbac* from output to input with correct phase can lead to oscilla&ons  ?orrect phase means a posi&ve feedbac* and it ta*es place due through stray capacitances  As reactance of stray capacitances decreases at higher frequencies resul&ng in increased feedbac*  Forcing the device to wor* as an oscillator instead of an amplier 2aria&on in +@   The bandwidth is consistent and varies with the center frequency when tuned over a wide range of input frequencies  As frequency increases the bandwidth (fB) increases Thus the selec&vity of the input lter changes over any appreciable range of input frequencies Coor selec&vity   The gains are not uniform over a very wide frequency range  1ue to higher frequencies ability to select desired signal is aDected 1ue to these drawbac*s TRF is rarely used

Modern usage Although the TRF design has been largely superseded by the superheterodyne receiver, with the advent of semiconductor electronics in the 1960s the design was resurrected and used in some simple integrated radio receivers for hobbyist radio pro!ects, "its, and low#end consumer products$ %ne e&le is the :3