The first heterodyne receivers. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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The first heterodyne receivers. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / radio reception

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At present, when the principle of heterodyne reception has long been widely known, almost every beginner shortwave radio amateur listens to the air using the simplest home-made direct conversion (heterodyne) receiver, few people know that the first heterodyne receivers appeared almost simultaneously with the invention of radio and long before creation of radio tubes.

The idea of the possibility of receiving telegraph signals on beats was first expressed in the 1890s by N. Tesla. He surprisingly correctly predicted the course of development of radio engineering even at a time when there were no practically applicable real high-frequency generators. According to his version, the essence of the method should be to superimpose local local oscillator oscillations with a slightly different frequency on the received signal. The resulting beats may be perceived by ear.

The idea of heterodyne reception could not be implemented for a long time due to the lack of undamped oscillation generators with a stable frequency. Spark and arc generators were of little use due to the wide spectrum and instability of oscillations. More stable oscillations were produced by electric machine generators. With a large number of poles and a high rotor speed, it was possible to obtain frequencies of tens of kilohertz. High-frequency machines were widely used in transmitting radio stations during the early period of the superlong wave craze.

One of the first heterodyne receivers was built by Professor R. A. Fessenden (German patent No. 207329 dated 4.06.1905/XNUMX/XNUMX "Receiver for wireless telegraphy"; his American application was filed three weeks later. The receiver circuit in modern notation is shown in the figure.

First heterodyne receivers

The antenna circuit, most likely, was tuned to the signal frequency by selecting the inductance of the coil L1. The BF1 telephones had two coils: a signal was supplied to one, and a current from the machine RF generator G1 was supplied to the other. Since there was no permanent magnet, the membrane was attracted equally by both positive and negative signal half-waves. Quadratic detection was obtained, and the beat signal became audible.

The name of R. A. Fessenden is relatively little known, and yet he created machine generators that were remarkable for that time. One of them with a capacity of 60 kW was installed at a radio station in Brant Rock, Massachusetts, USA. He worked at a frequency of 50 kHz, and the signal was transmitted by an antenna 128 m high. From there, at the end of 1906, the world's first broadcast was carried out.

Other attempts to create a heterodyne receiver were made by the German engineer R. Goldschmidt, a developer of machine RF generators with frequency multiplication. He used in the receiver a rotating wheel with contacts ("Goldschmidt's wheel"). interrupting the signal circuit with a frequency slightly different from the frequency of the signal. It was no longer a detector, but a key signal multiplier providing linear frequency conversion! The exact date of the creation of the receiver is unknown, but it probably happened a little later, since the main works of R. Goldschmidt date back to 1906 - 1911.

Author: V.Polyakov, Moscow

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