Security alarm radio transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications
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The radio transmitter circuit consists of:
- frequency generator 1 kHz on the elements DD1.3, DD1.4;
- infra-low frequency generator HaDD1.1, DD1.2;
- emitter follower transistor VT1;
- quartz oscillator on transistor VT2;
- power amplifier transistor VT3.
When connecting a security loop to point "A" of the circuit and a common wire, the radio transmitter does not work, and the entire circuit consumes a current of 25 μA.
(click to enlarge)
When the loop breaks at point "A" - the potential of the logical "1", the generator on DD1.1, DD1.2 is "braked" and periodically turns on the generator on DD1.3, DD1.4. EP on VT1 performs amplitude modulation of the RF signal.
With the nominal values of the elements of the generators indicated in the diagram, a signal is heard in the receiver, similar to the "busy" signal of the PBX. If it is necessary to have a constant tone, points "A" and "B" of the circuit must be short-circuited (when the device is used for radio control).
The radio transmitter signal can be received by AM and FM receivers.
The circuit is operable at a supply voltage of 5 ... 15 V.
ZQ1 quartz is used in the PK169 case, the chokes are wound on ferrite rings with diameters of 7 ... 10 mm with a wire with a diameter of 0,2 ... 0,3 mm (until the ring is filled). Coils L1 and L2 do not have frames. L1 is wound on a 04 mm mandrel with PEV 0,41 wire and contains 14 turns. L2 is wound on a mandrel 0 3 mm with PEV 0,8 wire (7 turns). The number of turns L1 and L2 should be considered indicative, because due to the large tolerances of the capacitances of the capacitors, the selection of the number of turns during tuning cannot be avoided. RL 3/2000, p.39.
Author: A. Lapshin (UR5HTC), Kremenchug; Publication: N. Bolshakov, rf.atnn.ru
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