The oscillator circuit consists of a low-frequency modulator (C1,C4,DD1.4,R1,R2), ultrasonic generator fluctuations (C3,C4,DD1.3,DD1.4,R3,R4), amplifier power transistors VT1-VT3 and radiator, which is used as high-frequency loudspeaker 4ГLW-1. When the value indicated in the diagram, the generator emits a frequency-modulated fluctuations in the range of 15....40 kHz. Frequency is regulated by the resistor R4, the modulation frequency is regulated by the resistor R2 in the range 2...10 Hz. If you make contact SB1 so that when unauthorized entry into the premises this the contact closes, the generator can operate as a siren burglar alarm, because it begins to radiate the modulation frequency fluctuations in the range 1000...2000 Hz.
It should be borne in mind that prolonged work in the same frequency band rats can to adapt, so you need resistors R2-R4 to change the parameters of the radiation 2-3 times a week. Can also use this example: the capacitor C4 to connect with pigtail, creating additional capacity, changing temperature and humidity. Then the frequency will be changed randomly.
Author: Alexey Bogachev, Perm; Publication: N. Bolshakov, rf.atnn.ru