Car radio alarm. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Car radio alarm. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Security devices and alarms

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On vehicles intended for the transport of valuable goods, radio signaling devices with a range of up to several hundred meters can be used. To install such a radio signaling device in a car, you must obtain permission. Such a radio signaling device consists of a VHF transmitter, switched on using one or more B1 micro-toggle switches, and a direct gain receiver.

The transmitter and receiver are tuned to a frequency of 27...28 MHz. A miniature radio transmitter with a whip antenna in the form of a piece of wire is installed at the front window in the cab of the car. The whip antenna of the radio receiver should be oriented to the antenna of the radio transmitter and the distance between these antennas should not exceed 20 ... 30 m.

The figure shows the diagrams of the receiving and transmitting parts of the radio guard.

(click to enlarge)

The receiver is made according to the direct amplification scheme on a 1MM60 or K2NT171 hybrid integrated circuit and a V5 transistor. Instead of a microcircuit, transistors such as KT315G or KT301 can be used. The selection of the emitted signal in the receiving part of the radio guard is carried out using the L1C2 oscillatory circuit, tuned to a frequency of 29 MHz. The amplification of the selected signal is carried out using an aperiodic amplifier on the transistor Y6. A full-wave detector V2V3 allows you to select a signal at a frequency of 1 ... 5 kHz, which is modulated by the transmitter signal.

The selected low-frequency signal is amplified in a three-stage direct-coupled amplifier V7 ... V9, and then fed to the base of the transistor V5, the collector load of which is the relay winding. The contacts of this relay can connect voltage to a lighting lamp, to a sound signal from a car, etc.

The correction coil L2 is wound on a resistor MLT-0,5 56 kOhm with a PEV 0,15 wire. 27 turns are wound around the resistor, which will provide an inductance of about 1,8 μH.

The coil L1 is frameless, it is made with a bare copper (preferably silver-plated) wire with a diameter of 1 mm on a blank with a diameter of 16 mm. After winding 15 turns, they are moved apart by a length of 20 mm and a tap is made from the middle. Capacitor C2 type KPK-M tune the circuit to the frequency of the transmitter.

The transmitter consists of two oscillators on transistors V1 and V2, one of which allows you to generate a low-frequency modulating signal, and the second - a high-frequency one. The high-frequency generator on V2 at high frequency is connected according to the common base circuit, which increases the generation stability. The modulating signal is taken from the winding of the transformer T and through the capacitor C3 enters the base of the transistor V2. As a transformer, a matching transformer from some small-sized radio receiver is used. The coil of the high-frequency generator L1 is the same as in the receiving part. Frequency tuning is performed by capacitor C5 of the KPK-M type. When setting up the transmitter, the presence of generation on the transistor V1 is checked by turning on the DEM-4M, DEMSH-1 capsule or a low-resistance earpiece with a winding resistance of 50 ... 100 Ohms in series with the primary winding 1 of the transformer. This produces a loud sound. In the absence of generation, it is necessary to swap the ends of any of the windings.

The frequency of sound and its volume can be changed by selecting capacitance C2. The presence of generation in a high-frequency generator can be checked using a detector indicator made on the inductance L0, the signal from which, after rectification by a diode V3 of type D9, is fed to the capsule. By selecting the coupling capacitance C6, stable generation is achieved, which is indicated by listening to the frequency of the modulating oscillator using a capsule. The indicator coil L0 is wound in the same way as the loop coil L1, but the number of turns should be less (10.,.12). When checking the presence of high-frequency generation, the detector indicator is installed at a distance of several tens of centimeters from the L1 circuit. The greatest operating range of the security device with a radiated power of 15 mW is ensured by fine tuning the L1C2 circuit of the receiver to the transmitter frequency, as well as with the same orientation of the receiving and transmitting antennas.

As the simplest antennas, a copper rod or a tube with a diameter of up to 10 mm and a length of several tens of centimeters (100 ... 120 cm) can be used. The transmitting antenna can be mounted horizontally directly in front of the front or rear window of the vehicle. The receiving antenna is installed horizontally and within line of sight on a balcony, at the end of a house, in a tent, etc.

The generation frequency of the transmitter is checked and set by a VHF receiver of the same frequency range (28 ... 30 MHz) or by a wavemeter. A vertically oriented car radio whip antenna can be used as a transmitting antenna. The receiving antenna can be made in the form of a piece of thick wire 1,5 m long.

See other articles Section Automobile. Security devices and alarms.

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