Page 19 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

recovering audio information from an AM signal. This type of diode circuit is

commonly called an envelope detector.
Alternatively, a transistor amplifier (Qi, RiB, R2B, and C2B) also can be used for
converting an AM signal into an audio signal by way of power detection. Using a
transistor power detector is a way of demodulating or detecting an AM signal by the
inherent distortion (nonlinear) characteristic of a transistor. Power detection is not
quite the same as envelope detection, but it has the advantage of converting the

AM signal to an audio signal and amplifying the audio signal as well.
Power-detection circuits are commonly used in regenerative radios and sometimes
in superheterodyne radios.
It should be noted that in more complex TRF radios, multiple tuned filter circuits

are used to provide better selectivity, or the ability to reduce interference from
adjacent channels, and multiple amplifiers are used to increase sensitivity.
Regener'ative Radio

This is probably the most efficient type of radio circuit ever invented. The principle
behind such a radio is to recirculate or feed back some of the signal from the
amplifier back to the RF filter section. This recirculation solves two problems in
terms of providing better selectivity and higher gain. But there was another

problem. Too much recircullation or regeneration caused the radio to OSCillate,
which caused a squealing effect on top of the program material (e.g., music or
voice) (Figure 1-2).