Intercom on a network of 220 volts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Telephony
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The use of such devices justifies itself in negotiations within the same house or neighboring houses, because. using a radio station at such distances is impractical, and the telephone is now paid by the minute.
The principle of operation of these devices is based on the fact that electromagnetic oscillations with a frequency of 10 kHz to 100 kHz can be transmitted through the wires of the electrical network, and they can freely propagate to the nearest transformer.
In its simplest form, this device is an RF generator (Fig. 1) and a VLF detector receiver (Fig. 2)
The oscillator is assembled according to the usual push-pull scheme. It is modulated in amplitude by the BM1 carbon microphone included in the power supply circuit of the VT2, VT3 collectors. Coils L1...L4 are placed in SB-12 or similar cores. It is important that L1 and L4 are identical in number of turns, wire diameter and winding method.
L1 contains 100 turns with a tap from the middle. Wire - with a diameter of 0,1 ... 0,15 mm. Both halves of the coil are wound in different sections of the frame, i.e. half in one section and half in the other.
L2 contains approximately 50 turns of wire with a diameter of 0,1 ... 0,15 mm and is wound over L1.
L4 - 100 turns; wound in the same way as L1, but without retraction.
L3 - 50 turns, over L4.
To increase the range, you can use UHF in the receiver, as well as a power amplifier in the transmitter. For better modulation, you can use a transistor modulator, preferably with a microphone compressor.
Do not greatly increase the power, as this leads to interference in equipment powered by the mains. You should also not increase the frequency above 150 kHz, as this leads to interference on the air.
Author: N. Marushkevich, Minsk; Publication: N. Bolshakov, rf.atnn.ru
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