Car radio. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Security devices and alarms
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In connection with the growth in the number of cars and the remoteness of garages from apartments, the issue of protecting cars at night in the courtyards of houses has become relevant. If stealing a car is quite difficult, then removing the emblem, pulling out the radio or battery is not a big deal. Most anti-theft devices only make it harder to start the car's engine, but do not protect against theft of contents.
There are devices that respond to swing, the actuating unit of which is a siren or a car signal. At night, they wake up not only the owner, but also the neighbors. Disconnecting the battery completely disables such devices.
From all these shortcomings, the proposed radio watchman is free. Let's take a look at his work.
(click to enlarge)
The radio watch consists of a high-frequency generator, a modulator and a swing sensor. In standby mode, the swing sensor is open and power is supplied only to the generator. The receiver, located in the apartment, is tuned to the carrier frequency of the generator by the disappearance of noise in the loudspeaker.
Thus, even when the battery is disconnected, the operation of the radio guard is determined by a sharp increase in noise, and this is also a sign of the health of the car-apartment line.
When touching the car, the rocking sensor B1 closes for a short time (Fig. 2). Through its contacts, power is supplied to the modulator and the capacitor C 1 is charged.
(click to enlarge)
After opening the sensor contacts, the modulator is powered from the capacitor until the next short circuit. The voltage of damped low-frequency oscillations from the output of the modulator modulates the high-frequency generator. At the same time, a loud intermittent alarm is heard in the receiver. The frequency of the high-frequency generator is determined by the quartz frequency (3..5 harmonics) and is in the ranges of 64...75 MHz or 88...108 MHz for the European standard. Coil L1 has 6 turns of PEL 0,6 wire on a frame with a diameter of 6 mm. Communication coil L2 - 2 turns PEL 0,3. The range of the radio watchman from inside the car without a connected antenna is up to 50 m. Several of these devices have been tested in operation for 2 years and have shown reliable operation.
Collected schemes, as well as consultations, can be obtained from the author.
Literature
- Mil G. Electronic remote control of models. - M.: DOSAAF, 1980.
Author: N.Martynyuk; Publication: N. Bolshakov, rf.atnn.ru
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