Regenerative circuit
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The regenerative circuit (or self-regenerative circuit') allows a signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor.
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Hiustory
Regenerative circuits were employed in early radio receivers, offering selectivity and sensitivity far beyond that available from a crystal radio receiver. Regenerative circuits were a great milestone in radio history. The inventor of FM radio, Edwin Armstrong, patented the regenerative circuit (invented while he was a junior in college, and patented 1914), the Super-regenerative circuit (patented 1922), and the Super Heterodyne receiver (patented 1918). Lee De Forest filed a patent in 1916 that became the cause of a contentious lawsuit with the prolific inventor Armstrong, whose patent for the regenerative circuit had been issued in 1914.
The lawsuit lasted twelve years, winding its way through the appeals process and ending up at the Supreme Court. The Court ruled in favor of De Forest, although the experts still disagree about whether the correct judgement had been issued. The regenerative radio made the most out of very few parts. When the parts became easier to obtain, the superheterodyne receiver replaced it for all serious work. The superheterodyne receiver is the most common receiver in use today.
Description
The secret to the regenerative radio receiver operation was the carefully controlled positive feedback. This also allowed the receiver to oscillate, allowing CW (Morse code) to be heard as beeps. The regenerative receiver is theoretically as sensitive as any radio can be, however, the adjustments are critical, and must be continuously monitored during listening. If misadjusted the receiver can transmit interference.
The superregenerative receiver
The superregenerative receiver uses a quenching oscillator to permit high positive regeneration of the radio amplifying stage, while quenching or keying the built up regenerative oscillation at an ultrasonic rate. This further improved the gain of the receiver while simplifying adjustment.