Currently, when the principle of heterodyne reception for a long time and is widely known, almost every beginner radio-shortwave listening with ether through a simple self-made direct conversion receiver (heterodyne), few people know that the first heterodyne receivers appeared almost simultaneously with the invention of radio and long before the establishment of tubes.
The thought of the possibility of reception of Telegraph signals on the beat, first expressed in 1890-ies N. Tesla. He surprisingly accurately predicted the course of the development of radio engineering back when there was practically applicable to the real generators of high frequency. In his version, the inventive method should be applied to the received signal of the local oscillation of the local oscillator with slightly different frequency. The generated beats may be seen at the hearing.
The idea of heterodyne reception for a long time failed to exercise due to the lack of generators sustained oscillations with a stable frequency. Spark and arc the generators were not useful because of the wide variety and instability oscillations. More stable oscillations gave dynamoelectric generators. When a large number poles and high-speed rotation of the rotor was able to obtain frequencies in the tens kilohertz. Machine high frequency is widely used for transmitting radio stations in the early period of fascination with the extra-long waves.
One of the first heterodyne receivers built by Professor R. A. Fessenden (German patent No. 207329 from 4.06.1905 "Receiver for wireless telegraphy"; it is the us application was filed three weeks later. The receiver circuit in modern notation shown in the figure.
The antenna circuit is likely tuned to the frequency selection signal the inductance of the coil L1. In phones ВF1 had two coils: one summed signal to the other - the current machine from the RF generator G1. Since a permanent magnet is absent, the membrane is attracted equally as the positive and negative half waves of the signals. Worked quadratic detection, and the signal of the beats became audible.
The name R. A. Fessenden relatively little is known, and because they were created wonderful for that time machine generators. One 60-kW was installed at the radio station in Brant Rock, Massachusetts, USA. He worked at a frequency of 50 kHz, and the signal transmitted by the antenna height of 128 m. from There to the end 1906 was held the world's first radio transmission.
Other attempts to create a heterodyne receiver had been German engineer R. Goldschmidt, a developer of machine RF generators with multiplication frequency. He applied at the receiver, the rotating wheel with contacts ("wheel Goldschmidt"). a terminating circuit of a signal with a frequency slightly different from the frequency of the signal. It was not the detector, and the key multiplier signals, providing a linear frequency conversion! The exact date of the creation of the receiver unknown, but probably it happened a bit later, because the main the work of R. Goldschmidt belong to 1906 - 1911.
Author: V. Polyakov, Moscow