Cell phone radiation detector. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Field strength detectors
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The proposed device captures the fact that the transmitter of a nearby cell phone is turned on.
Phone radiation is not difficult to detect from a high-frequency signal induced in a nearby antenna. To do this, it is enough to make a device, the scheme of which is shown in Fig. one.
Rice. 1 (click to enlarge)
The diode VD1 serves as the amplitude detector of microwave oscillations. If the amplitude of the received signal is large enough, the output voltage of the detector will open the transistor VT1 and at the output of the single vibrator DD1.1-DD1.2, a high logic level pulse will appear, which will allow the operation of the multivibrator DD1.3-DD1.4). A package of pulses amplified by transistors VT2 and VT3 will be reproduced by the BA1 head as a loud click. So the device will react to the output of a cell phone on the air, even for a very short time.
Therefore, the device is supplemented with a memory and light indication unit, similar to that described by the author in the article "Electronic "tag"" ("Radio", 2002, No. 11, pp. 33, 34).
The printed circuit board of the device is shown in fig. 2. It is made of double-sided foil fiberglass with a thickness of 1,5 mm. The foil on the part installation side is used as a common wire and screen, and an antenna vibrator is formed from it. The connections of the outputs of the parts with a common wire are shown in black squares. A square with a bright dot in the center is a jumper passing through the board, connecting the negative terminal of capacitor C7 to a common wire.
Fig. 2.
All resistors - MLT-0,125. Capacitors C1 - KD-1, C2-C6 - KM-6 or K10-176, C7 - any oxide of suitable sizes with the least possible leakage (it should not affect the overall power consumption of the device). HL1 LED - any one that has a sufficiently bright glow at a current of 7 ... 8 mA. Sound emitting head VA1 - any resistance 50 Ohm.
A very important element - the VD1 diode - should have the smallest possible capacitance. Here are some of the diodes that are suitable in terms of parameters and design (their capacitance at zero bias is indicated in brackets): 2 pF), KD926A (0,35 pF), KD516A (0,5 pF).
The length of the half-wave vibrator for the 900 MHz band should be approximately 150 mm, and for 1800 MHz it should be half that. However, experience has shown that in most cases there is no need for a full-size antenna.
The signal of the LX677 Ericsson cell phone with a frequency of 860 MHz is reliably received on the "printed" vibrator of the device from a distance of 0,15 m. 2. They introduce pieces of hard wires of the desired length. For the 900 MHz band - approximately 35 mm, for 450 MHz - 110 mm. Extension cords will require small holes in the side walls of the case.
The extremely low power consumption of the device in standby mode (less than 5 μA) allows you to use almost any 6 V source to power it. A power switch is not required - the energy of such a battery is enough for at least a year of continuous operation.
The case of the device can be glued from high-impact polystyrene, its dimensions are 85x57x25 mm.
Author: Yu. Vinogradov, Moscow; Publication: cxem.net
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