page_title: Radio receiver
section_title: Neutrodyne receiver
hierarchical_section_title: Radio receiver / History / Vacuum tube era / Neutrodyne receiver
caption_attribution_description: English: The first neutrodyne radio receiver, presented by Louis Alan Hazeltine in a lecture on March 2, 1923 titled "Tuned radio frequency amplification with neutralization of capacity coupling" to the Radio Club of America at Columbia University, New York. Invented by Hazeltine at Stevens Institute, Neutrodyne receivers were widely sold until they were replaced by superheterodynes in the 1930s. The Neutrodyne circuit was a type of Tuned Radio Frequency (TRF) receiver. In a TRF receiver, the radio signal from the antenna is amplified at its original radio frequency by one or more vacuum tubes before it is rectified in a detector to extract the audio signal. However the triode tubes available at the time had high interelectrode capacitance between the plate and the grid which allowed signal from the output plate circuit to feed back into the grid, causing the tube to oscillate This produced interfering sounds, shrieks, whistles, and groans from the speaker. The Neutrodyne circuit solved this problem by adding a circuit which coupled some of the signal from plate to grid circuit with the opposite phase, canceling the feedback through the interelectrode capacitance. This was usually done with an additional winding on the interstage coupling transformers. Hazeltine's prototype Neutrodyne is shown here, being examined by members of the Radio Club of America. It had five tubes: two stages of RF amplification, a detector, and two stages of audio amplification. The interstage coupling coils between the tube stages that provide the neutralizing signal are visible, mounted diagonally, between the tubes. The rectangular objects in foreground are "B" batteries providing the plate voltage, about 45 V, to the tubes. They are special types with multiple taps, allowing the plate voltage to be changed by cutting more or fewer cells into the circuit.
context_page_description: In radio communications, a radio receiver, also known as a receiver, a wireless or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. The antenna intercepts radio waves and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The receiver uses electronic filters to separate the desired radio frequency signal from all the other signals picked up by the antenna, an electronic amplifier to increase the power of the signal for further processing, and finally recovers the desired information through demodulation.
  Radio receivers are essential components of all systems that use radio. The information produced by the receiver may be in the form of sound, moving images, or digital data. A radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar type of radio receiver for most people is a broadcast radio receiver, which reproduces sound transmitted by radio broadcasting stations, historically the first mass-market radio application.
context_section_description: The Neutrodyne receiver, invented in 1922 by Louis Hazeltine, was a TRF receiver with a "neutralizing" circuit added to each radio amplification stage to cancel the feedback to prevent the oscillations which caused the annoying whistles in the TRF.  In the neutralizing circuit a capacitor fed a feedback current from the plate circuit to the grid circuit which was 180° out of phase with the feedback which caused the oscillation, canceling it.  The Neutrodyne was popular until the advent of cheap tetrode tubes around 1930.
caption: Hazeltine's prototype Neutrodyne receiver, presented at a March 2, 1923 meeting of the Radio Society of America at Columbia University.
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