Burglar alarm transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling
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I propose another transmitter circuit for guarding remote objects (garage, barn, car, etc.). The circuit (Fig. 1) consists of a master oscillator, an intermediate amplifier and an output stage. Its distinctive feature is the master oscillator, the sufficient stability of which is achieved by using a piece of coaxial cable as a circuit. The rest of the cascades have no singularities. The master oscillator is tuned to a free section of the VHF broadcasting range (63 ... 74 MHz). The signal is received on a conventional VHF receiver.
Fig.1 (click to enlarge)
A modulator generator is assembled on the 564LE5 chip. The frequency deviation is sufficient to receive a signal on a conventional broadcast receiver.
The master oscillator coil L1 is made of a piece of thin coaxial cable with a characteristic impedance of 75 ohms and has a length of about 180 mm for the specified range. You may have to pick it up (lengthening or shortening) for the selected frequency.
Coils L2, L3 are wound on a frame with a diameter of 4 mm. L2 contains 6 turns of PEL 0.3 wire, and the communication coil L3 contains 2 turns of the same wire wound side by side. Coil L4 - frameless, contains 6 turns of PEL 0.5 wire wound on a mandrel with a diameter of 4 mm.
The antenna is made of stranded wire. Its length is equal to a quarter of the wavelength at which the transmitter operates. In my case, it is about 1 meter.
Installation made on "piglets" according to the method of Zhutyaev on the board of their one-sided fiberglass (Fig. 2). The 564LE5 chip is soldered on a "breadboard" and glued to the main board.
Ris.2
Attention must be paid to the rigid fastening of the coaxial cable section (L1). It can be placed along the perimeter of the board and fixed with soldered brackets made of copper wire with a diameter of 0,8 mm. The entire board is placed in a metal box (Fig. 3).
Ris.3
The security loop can be made on microbuttons, and even better on reed switches. I use this method: I mask the reed switch on a flat surface, pull the fishing line at a small height from the floor (20 ... 40 cm), fasten one end of it, and tie a small magnet to the second and put it on the surface where the reed switch is located - that's it, the chain closed. It is better to put up several such barriers. The whole system is quite inconspicuous, and when the magnet jumps off the reed switch, the attacker cannot find the original place of its installation.
Literature:
1. Coaxial cable - "coil" of inductance. QST, May 1981
Author: Nikolay Bolshakov, RA3TOX, Nizhny Novgorod; Publication: N. Bolshakov, rf.atnn.ru
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