Encyclopedia of radio electronics and electrical engineering / radio reception

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I managed to build a receiver powered by the energy of the transmitting radio station. And I think it will be of interest to many radio amateurs. I was encouraged to design by a good friend of mine. He received a piece of land near Krasnoyarsk. And since electricity will not be brought there for another century, and sometimes the salary is not enough even to power the transistor, he asked me to make a simple detector receiver in order to keep abreast of the news.

Having collected materials related to this type of equipment, I set to work. And it turned out that the schemes proposed in mass literature and magazines were, to put it mildly, ill-conceived. In particular, this applies to the circuits of detector receivers using additional amplifying stages on transistors.

Here is an example of one of the recommended schemes. The rectifying diode is installed in series from the antenna to the fed transistor stage. As a result, for normal operation of the receiver, a voltage equal to the sum of the drop voltages across the diode and the required amplifier will be required.

This drawback can be eliminated by installing a rectifying diode in parallel with the powered stage. But then there is the question of selectivity. In connection with the shunting of the resonant circuit with the equivalent resistance of the amplifying stage, the receiver begins to catch the programs of all operating stations and is very responsive to tuning. The decision suggests itself to separate the circuit from the amplifier stage. This turned out to be possible if a circuit with a series resonance and power supply to the amplifying stage was used. At the same time, the selectivity increased sharply with fine tuning to the transmitting station.

With such a receiver, you can also increase the number of amplifying stages. By introducing a reflex circuit, when the same transistors are used in the HF and LF amplification modes, I was able to significantly increase the sound volume of the received stations.

Schematic diagram of the reflex receiver 3-V-3.

The proposed scheme is a 3-V-3 reflex receiver, which allows receiving radio stations in the range of long and medium waves with satisfactory loudness.

The device includes a resonant circuit with series resonance (C1, L1), a three-stage reflex amplifier (VT1-VT3), an RF signal detector (VD1-VD3), a transistor power supply rectifier (VD4).

The design of the receiver depends on the type and dimensions of the parts used. As an inductor, circuits wound on cylindrical, square frames, as well as on a ferrite rod are suitable. Transistors fit germanium 400th and 300th series with h21B not lower than 40. Diodes - germanium type D2 or D9.

Telephone capsule - type DEM-Sh or similar with a resistance of 60-100 ohms.

My receiver picks up radio stations at a distance of 40 km from Krasnoyarsk with an antenna 20 m long and 10 m high.

Literature

1. Detector radio // Radio amateur, 1994, No. 2, p. 36.
2. Is everything a detector? // Model designer, 1996, No. 11, p. 14 - 15.
3. Receiver without power source // Radio, 1993, No. 11, p. fourteen.
4. Simple radio // Model designer, 1982, No. 7, p. 40.

Author: Yu.Bondarenko

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