Using network wires as a security alarm loop. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling
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The operation of the device is based on the property that high-frequency vibrations with a frequency of up to 150 kHz can be transmitted through the wires of the electrical network. They freely propagate to the nearest transformer. The same principle is used in the transmission of three stations over radio transmission wires, two of which are transmitted with frequency modulation of 78 and 120 kHz.
At frequencies above 150 kHz, part of the RF energy begins to radiate into the air, creating interference. For this reason, it is not advisable to use higher frequencies for transmitting information over network wires.
At the protected object, a device block is installed, the electrical circuit of which is shown in fig. 2.38. It consists of two oscillators. The first generator on the elements of the chip D1.1 and D1.2 generates pulses with a frequency of 2 Hz and modulates the second generator (D1.3 and D1.4), operating at a frequency of 70 kHz, fig. 2.39. A resonant amplifier is assembled on transistor VT1. From the output of the secondary winding of the transformer, bundles of high-frequency oscillations through capacitors C5 and C6 enter the network.
The device is powered directly from the network according to a transformerless circuit, which allows to reduce its dimensions. The connection is made in compliance with the phasing indicated in the diagram.
With proper installation, the circuit will work immediately, and the tuning is to obtain resonance in the circuit of the L2 coil at a frequency of 70 kHz. It is better to check the circuit when it is powered from a stationary source.
As a receiver, you can use the amplifier circuit shown in Fig. 2.40, and if you need to get a longer range of work, the scheme of fig. 2.13 with minor changes in the input circuit and coil design.
Coils L1 and L3 are the same and are made in ferrite cups SB-12 or similar from the intermediate frequency circuits (465 kHz) of the receivers. They should provide for the possibility of tuning with the help of cores. Winding 1 contains 160 turns, 2 - 50 turns with PELSHO wire with a diameter of 0,08 mm.
Fig. 2.38. Electrical diagram of the unit (click to enlarge)
Rice. 2.39. The shape of the signals explaining the operation of the circuit
Inductor L2 contains 200 turns with the same wire on a ferrite ring 600 ... 2000NM, size K10x6x3 mm. The parameters of the L4 coil are the same as those shown in fig. 2.17.
In the circuits, resistors of the MLT type are used, capacitors C2 of the K53-18 type for 20 V; C5, C6, C7, C8 - type K73-17V for the corresponding operating voltage. The remaining capacitors are of the K10-17 type or any small-sized ones.
Rice. 2.40. Receiver unit (click to enlarge)
Rice. 2.41. Topology of the printed circuit board of the security unit
The topology of a single-sided printed circuit board for the protection unit circuit is shown in fig. 2.41 (the dotted line shows two jumpers that are installed before the installation of the elements).
Publication: cxem.net
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