When the value indicated in the diagram, the generator emits a frequency-modulated oscillations in the range of 15 to 40 kHz. The oscillator frequency is adjustable by the resistor R4, the modulation frequency is governed by the resistor R2 in the range 2...10 Hz.
It must be borne in mind that the ultrasonic waves emitted by this generator may adversely affect the nervous system of humans and domestic animals. A long stay in a room with a working generator can cause headache, nausea, and other discomfort, so include it immediately before leaving the premises.
If you set the contact S1 in such a way that an unauthorized entry into the premises, this contact closes, the generator can also operate as a burglar alarm siren, because it begins to emit modulated by frequency fluctuations in the range of 1000...2000 Hz.
It should be borne in mind that in continuous operation in the same frequency band rats can adapt, so you need resistors R2 and R4 to change the parameters of the radiation 2...3 times a week. You can also apply this technique: the capacitor C4 to connect with pigtail, creating additional capacity, variable temperature, humidity, wind (if the wire output) and Then the frequency will change at random.
Author: V. Boroday, Zaporozhye; Publication: N. Bolshakov, rf.atnn.ru