Electronic eavesdropping device detector circuit description

The article introduces the electronic eavesdropping equipment detector circuit. The circuit is very simple, very helpful. If you understand this principle is not very thorough, it is recommended to understand this circuit an important component: 2N2222 . Detector detects an RF signal ranging from 1 to 1000 MHz. Figure 1 shows a schematic diagram of the detector. When the electron wrong operation, it emits radio signals. This signal is the receive antenna (point 1 in Figure 1), is applied to the base of transistor TR1 through a high-pass filter (a filter, allows high frequencies). The high pass filter comprises a capacitor C4, C5 and resistor R7. When the low-frequency signal is applied to the input filter capacitor C4 and C5 as an open operation switches and filters reject low frequency signals. The high-pass filter cutoff frequency is defined as the 60 Hz reject any interference from the power supply. Common collector of transistor TR1 is connected, it is used to amplify the signal. Provided 10 db of gain is a signal that a different frequency range 1 - 1000 MHz. This resistor R1, R2 R8 form a biasing network for the transistor TR1. The amplified signal is then applied, via the capacitor C6, the anode of the diode D1. This diode is made especially for the operation at high frequencies because ordinary diode can not conductive condition to the closing conditions are very fast to prevent reverse current. However, the diode operating at high frequency lead to the beginning of the negative half cycle of conduction. The scaling potentiometer terminal P1 of the signal applied to the diode D1 and the inverting input (Pin 2) of the operational amplifier A1. ? Operational amplifier A1 is configured as a very high gain amplifier. The value obtained is defined as the capacitor C8 and resistor R6 and R12. No signal input from the antenna A1 and the output pin 1 is close to the ground potential. Upon detection of a signal, the antenna range of 1 - 1000 MHz, it applies to the base of transistor TR1 produce the negative voltage at the cathode of diode D1. The voltage applied to the inverting input of A1, amplified and inverted signal to produce a positive output pin 1. After the second phase of the op amp. A1 is a voltage controlled oscillator (VCO). Controlling the oscillation frequency of the VCO output voltage of operational amplifier A1. Operational amplifier A2, A4, as the resistance, R13 R11, R14, R16 "is given, R19 R18 R17,,,,, R23 R20 R21, capacitors, transistors C9 TR2 arranged to form a voltage-controlled oscillator (VCO), scope of audio as the output of A1 increases, so that the VCO frequency is increased. VCO output, the pin 8 of operational amplifier A4, fed to the input of A3, configured as a non-inverting unity gain (buffer) amplifier. A3 output is used to drive transistor tomb, thus driving the output speaker. 

Technical Specifications – Characteristics
Supply voltage :	9V(DC)
Dissipation current:	30mA (max)
Detection range:	1 – 1000 MHz
Acoustic indication using a loudspeaker
Sensitivity adjustment using a potentiometer.   Parts List Resistors : Capacitors : R1?? =? 39 KOhm C1? = 10nF ceramic R2?? =? 470 Ohm C2? =? 4,7 мF/16V electrolytic R3?? =? 22 Ohm C3? =? 10nF ceramic R4?? =? 100 Ohm C4? =? 1nF ceramic R5?? =? 560 Ohm C5? =? 10nF ceramic R6?? =? 1 MOhm C6? =? 10nF ceramic R7?? =? 220 Ohm C7? =? 10nF ceramic R8?? = 100 KЩ C8? =? 10nF ceramic R9?? =? 4,7 KOhm C9? =?? 4,7nF ceramic R10 =? 1,5 KOhm C10 =? 10 мF/16V electrolytic R11 =? 10 KOhm Chip : R12 =? 220 Ohm IC1 =? МC3403P Motorola R13 =? 10 KOhm Transistors : R14 =? 100 KOhm TR1 =? BFR 90A R15 =? 470 Ohm TR2 =? 2N2222 R16 =? 47 KOhm TR3 =? 2N2222 R17 =? 47 KOhm Diode : R18 =? 1 KOhm D1 = NTE 112 R19 =? 10 KOhm Potesiometer : R20 =? 100 KOhm P1 = 4,7K Linear potesiometer R21 =? 47 KOhm Other : R22 =? 10 KOhm БNT = telescopic antenna. Radio type. R23 =? 47 KOhm LS = Loundspeaker 8 Ohm

 

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