High-frequency radio emission indicator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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High-frequency radio emission indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Indicators, detectors

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Using this indicator, you can detect a source of high-frequency radiation and, in conventional units, set its level. The device will help detect a spy "bug", determine the radiation of a microwave oven, a cell phone, as well as the presence of significant radiation in your apartment, for example, from a taxi or cellular antenna, cable TV, located on the roof of your multi-storey building.

Here is one real example - the residents of one of the high-rise apartments began to complain that cell phones were not working in their apartment, and there was no connection at all in the hallway. Another neighbor, from the apartment above, complained about the impossibility of receiving television and radio broadcasts on the built-in antenna. The third neighbor constantly had malfunctions in the built-in computers of the air conditioner and washing machine. The study of apartments and part of the house using this indicator showed that the source of powerful interference is the drop cable laid along the ventilation shaft from the taxi service antenna illegally installed on the roof of the house. Moreover, the apartment of the owner of this service was on the ground floor, and the cable passed to the antenna through all 16 floors of the house, generously distributing RF interference throughout the entrance.

(click to enlarge)

The indicator works as follows. In the presence of RF radiation, the indicator emits a tonal sound. The sensitivity threshold is set by a variable resistor R4, by the angle of rotation of the handle of which one can judge the level of RF radiation.

The antenna is a dipole of two wires, each 75 mm long. Between them is the input coil L1. The location is almost like in the schematic diagram.

The signal received by the antenna from the L1 coil is fed to the URF on the AT-32011 microwave transistor. Thanks to this cascade, the device has a high sensitivity.

Through the coupling capacitor C2, the amplified signal is fed to the detector diode assembly HSMS-2856, in which the microwave diodes. The detector is made according to the voltage doubling scheme. From the divider on resistors R4 and R6, a forward bias voltage is supplied to the diodes. This voltage creates a direct current, which increases the sensitivity of the detector, and creates a constant component at the output of the detector (on resistor R4). By adjusting the value of this constant component (resistor R1.1), you can set the switching threshold of element DXNUMX.

As soon as the voltage at R6 exceeds the switching threshold D1.1 (and the voltage at R6 is the sum of the DC bias voltage with the voltage received from the detector), a logic zero occurs at the output of D1.1, which causes the multivibrator D1.2-D1.3 to start. 1 and the sound of the piezoelectric buzzer BXNUMX.

Details. The HSMS-2852 diode assembly can be replaced with almost any two microwave diodes or a similar assembly.

I cannot offer a replacement for the VT1 transistor, but I can state with full responsibility that, subject to a decrease in sensitivity, this transistor can be abandoned by connecting the capacitor C1 directly to the assembly diodes VD1 (instead of C2). This version of the indicator (without VT1) was also made and tested. Subjectively, the sensitivity decreased by five times, but remained sufficient to receive a signal from a cell phone at a distance of 2-3 meters.

See other articles Section Indicators, detectors.

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