RF noise generator to block radio traffic. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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RF noise generator to block radio traffic

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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For security purposes, it may be necessary to prevent radio traffic near or inside an object. For this purpose, a simple device is suitable, the circuit of which is shown in Figure 1.

Fig.1. Schematic diagram of the RF noise generator

The electronic unit is based on the KR1006VI1 integrated circuit, which, in terms of its functionality, is capable of functioning as an oscillation generator in the range from fractions of a hertz to radio frequencies. Such a noise generator can "close" a certain spectrum of radio frequencies, including the civilian 27 MHz band. The transmitter antenna is the L1 choke, which is effective as a radiator only in the radio frequency band. As the frequency decreases, the inductor begins to act simply as an electrical conductor, shorting the output signal to ground. The required output frequency of the generator is set using a variable resistor R1 (it must have a linear characteristic).

The transmitter power is very low. It is able to jam the air in a wide band of radio frequencies only within 3 ... 5 m, which is quite suitable, for example, for the security of one office. If you connect a piece of stranded unshielded wire 3 ... 1 mm long as an antenna to terminal 100 DA120 at the junction with the inductor, the range of the transmitter will increase to 10 ... 15 m, which is already quite enough to block all kinds of "bugs" installed next to the front door of the room.

It is convenient to combine the power switch S1 with a variable resistor R1. All fixed resistors type MLT-0,25. Any non-polar capacitors. Throttle type DM-0,4. The power supply voltage of the node can be from 5 to 12V (at a higher voltage, the generation fails). The current consumption fluctuates slightly depending on the position of the resistor R1 (transmitter frequency) within 12...18 mA. The output frequency is determined by the elements R1 and R2 and the capacitance of the capacitor C2.

It is more convenient to tune the circuit to a given frequency using a variable resistor R1. After the desired frequency is set, it is necessary to turn off the power to the node and replace the variable resistor with a constant of the corresponding resistance.

An increase in the resistance of the resistor R1 causes a decrease in the frequency of the output signal, and a decrease in resistance leads to an increase in the operating frequency of the transmitter.

Even a slight decrease in the capacitance of the capacitor C2 causes a significant increase in the output frequency. As in any high-frequency circuit, the leads of all components should be shortened as much as possible.

Inductor L1 must be installed at some distance from the DA1 chip and other components. The body of the device must be made of plexiglass or other dielectric material.

Before the first test of the node near it, turn on the radio receiver (civilian radio station 27 MHz in receive mode) and control the operation of the generator by the sound from the speaker. Setting up the device consists in setting the output frequency of the generator. When you first turn on and approach the human hands to the elements of the device and the throttle, the output frequency will change under the external influence of the capacitance of the human hands. After making sure that the node is working and setting the output frequency, it is necessary to fix each element (glue it with non-conductive current with quick-drying glue or epoxy resin) to the board to give mechanical stability. After 10 ... 12 hours after the glue has dried, you can start using the noise generator.

Author: A.P. Kashkarov, St. Petersburg; Publication: radioradar.net

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