Tuned radio frequency receiver

Posted on Feb 6, 2014

A tuned radio frequency receiver (TRF receiver) is a radio receiver that is usually composed of several tuned radio frequency amplifiers followed by circuits to detect and amplify the audio signal. A 3 stage TRF receiver includes a RF stage, a detector stage and an audio stage. Generally, 2 or 3 RF amplifiers are required to filter and amplify

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the received signal to a level sufficient to drive the detector stage. The detector converts RF signals directly to information, and the audio stage amplifies the information signal to a usable level. Prevalent in the early 20th century, it can be difficult to operate because each stage must be individually tuned to the station`s frequency. It was replaced by the Superheterodyne receiver invented by Edwin Armstrong. The TRF receiver was patented in 1916 by Ernst Alexanderson. His concept was that each stage would amplify the desired signal while reducing the interfering ones. The final stage was often simply a grid-leak detector. The radio schematic above shows a typical TRF receiver. This particular radio uses a six tube design utilizing triode tubes. It has two radio frequency amplifiers, one grid-leak detector/amplifier and three class A` audio amplifiers. The significance of the term "tuned radio frequency" is best understood when compared to the Superheterodyne receiver. A tuned radio frequency receiver actually tunes the receiver on the true radio frequency whereas the Superheterodyne receiver, tunes the desired signal after conversion to an intermediate frequency. Many homemade radios constructed by enthusiasts today, are tuned radio receivers, and these can range from single stage to multi-stage receivers. A problem with the TRF receiver is that interelectrode capacitance causes oscillations and other modes in the...

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