Neutrodyne

A major defect of the TRF receiver was that, due to the high interelectrode capacitance of early triode vacuum tubes, feedback within the RF amplifier stages gave them a tendency to oscillate, creating unwanted radio frequency alternating currents.These parasitic oscillations mixed with the carrier wave in the detector, creating heterodynes (beat notes) in the audio frequency range, which were heard as annoying whistles and howls from the speaker.[3] At the time, RCA held a virtual monopoly over commercial radio receiver production due to its ownership of the rights to the Armstrong regenerative and superheterodyne circuits.After manufacture each tuned amplifier stage had to be neutralized, adjusted to cancel feedback; after this the set would not produce the parasitic oscillations which caused the objectionable noises.The Neutrodyne neutralization technique continues to be used in other applications to suppress parasitic oscillation, such as in RF power amplifiers in radio transmitters.
Neutrodyne receiver used on US President Warren Harding's yacht, the Mayflower
radio receiverLouis Hazeltinetuned radio frequencycapacitancetriodeparasitic oscillationsamplifierscapacitorssuperheterodynetuned radio frequency (TRF) receiverdetectoraudio amplifiervacuum tubesfeedbackoscillatecarrier waveheterodynesregenerativetuned amplifierNorth AmericatetrodeMillerEdwin Armstrongparasitic oscillationradio transmittersMiller capacitanceCrystal radio receiverLow IF receiverRegenerative radio receiverSuperheterodyne receiverTuned radio frequency receiverWayback Machine