ABSTRACT
This
handy, pocket-size mobile transmission detector or sniffer can sense the
presence of an activated mobile cell phone from a distance of one and-a-half
meters. So it can be used to prevent use of mobile phones in examination halls,
confidential rooms, etc. It is also useful for detecting the use of mobile
phone for Spying and unauthorized video transmission. The circuit can detect the
incoming and outgoing calls, SMS and video transmission even if the mobile
phone is kept in the silent mode. The moment the Bug detects RF
transmission signal from an activated mobile phone, it starts sounding a beep
alarm and the LED blinks. The alarm
continues until the signal transmission ceases. Assemble the circuit on a
general purpose PCB as compact as possible and enclose in a small box like junk
mobile case. As mentioned earlier, capacitor C3 should have a lead length of 18
mm with lead spacing of 8 mm. Carefully solder the capacitor in standing
position with equal spacing of the leads. The response can be optimized by
trimming the lead length of C3 for the desired frequency. You may use a short
telescopic type antenna.
Use the miniature 12V battery of a remote control and a small buzzer to make the gadget pocket-size. The unit will give the warning indication if someone uses Mobile phone within a radius of 1.5 meters.
CHAPTER-1
OVERVIEW OF MOBILE BUG
IC1 is designed
as a differential amplifier Non inverting input is connected to the potential
divider R1, R2. Capacitor C2 keeps the non inverting input signal stable for
easy swing to + or – R3 is the feedback resistor
IC1 functions as
a current to voltage converter, since it converts the tiny current released by
the 0.22 capacitor as output voltage.
At power on
output go high and LED lights for a short period. This is because + input gets
more voltage than the – input. After a few seconds, output goes low because the
output current passes to the – input through R2. Meanwhile, capacitor C1 also
charges. So that both the inputs gets almost equal voltage and the output
remains low. 0.22 capacitor (no other capacitor can be substituted) remains
fully charged in the standby state.
When the high
frequency radiation from the mobile phone is sensed by the circuit, 0.22 cap
discharges its stored current to the + input of IC1 and its output goes high
momentarily. (in the standby state, output of the differential amplifier is low
since both inputs get equal voltage of 0.5 volts or more). Any increase in
voltage at + input will change the output state to high.
Purpose of the circuit
This circuit is
intended to detect unauthorized use of mobile phones in examination halls,
confidential rooms etc. It also helps to detect unauthorized video and audio
recordings. It detects the signal from mobile phones even if it is kept in the
silent mode. It also detects SMS.
CONCEPT
Mobile phone
uses RF with a wavelength of 30cm at 872 to 2170 MHz. That is the signal is
high frequency with huge energy. When the mobile phone is active, it transmits
the signal in the form of sine wave which passes through the space. The encoded
audio/video signal contains electromagnetic radiation which is picked up by the
receiver in the base station. Mobile phone system is referred to as “Cellular
Telephone system” because the coverage area is divided into “cells” each of
which has a base station. The transmitter power of the modern 2G antenna in the
base station is 20-100 watts.
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