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How to Make an RF Bug Detector

While there are many tutorials for electronic hobbyists on building small FM transmitters, there are only a few circuits dedicated to detecting them. However, building an RF bug transmitter is very useful in learning about radio frequency technology. There are many different ways to design a RF bug transmitter. This article will focus on assembling the circuit published IQ Technologies.

Things You'll Need

Printed circuit board (PCB)
Soldering iron
Solder
PCB holder
1 resistor, 39 kiloohms
2 resistors, 470 ohms
1 resistor, 22 ohms
1 resistor, 100 ohms
1 resistor, 560 ohms
1 resistor, 1 megaohm
2 resistors, 220 ohms
3 resistors, 100 kiloohms
1 resistor, 4,7 kiloohms
1 resistor, 1,5 kiloohms
4 resistors, 10 kiloohms
4 resistors, 47 kiloohms
1 resistor, 1 kiloohm
6 ceramic capacitors, 10 nanofarads
1 electrolytic capacitor, 4,7 microfarads/16 volts
1 ceramic capacitor, 1 nanofarad
1 ceramic capacitor, 4,7 nanofarads
1 electrolytic capacitor, 10 microfarads/16 volts
1 ΜC3403P Motorola integrated circuit
1 BFR 90A transistor
2 transistors, 2N2222
1 NTE 112 diode
1 linear potentiometer, 4,7 kiloohms
1 telescopic antenna, radio type
1 loudspeaker, 8 ohms
1 battery clip, 9 volts
1 battery, 9 volts

Instructions

- 1
  Mount the PCB. Anything that will hold the PCB and allow you to work with both hands will do. Most electronics store sell a helping-hands device that carries out just this function.
- 2
  Connect the resistors, which range from 22 ohms to one megaohm. There are more resistors on this board than any other type of component, 23 in all. Each resistor is a carbon film, through-hole type. When soldering the resistor to the board, push its wire leads through the designated holes in the PCB and then solder the component in place. Finally, cut of the excess leads.
- 3
  Connect the capacitors. This circuit has both ceramic disc and electrolytic capacitors. Solder them in the same manner as the resistors.
- 4
  Connect the transistors. These are small half cylinders that function as switches in the RF bug detecting circuit. They have three wire leads instead of the two usually seen on resistors and capacitors. Since they are more sensitive to heat, clip a heat sink onto whichever lead you are soldering to dissipate excess heat from the iron.
- 5
  Connect the diode, which is shaped like the resistors, but smaller. It has a specific polarity, however, and you must correctly position the positive anode and the negative cathode. Usually, one side of the component symbol on the circuit board is marked with a plus sign to indicate the position of the anode.
- 6
  Install the integrated circuit. For their RF bug detector circuit, IQ Technologies uses the MC3403P integrated circuit. The MC3403P is a 14-pin IC consisting of an array of three operational amplifiers. Do not solder the chip directly to the PCB, as this will likely damage the IC. Instead, solder a 14-pin socket to the board and push the chip into the socket.
- 7
  Connect the potentiometer. This is a variable resistor, which partially blocks electric current. However, unlike the other resistors on the board, you can adjust the amount of current blocked by a potentiometer using its control nob.
- 8
  Connect a telescopic antenna. It is through the antenna that the bug detector finds radio frequency waves emanating from the transmitter.
- 9
  Connect the eight ohm loudspeaker. When the antenna picks up signals from a bug transmitter, a tone sounds from the loudspeaker.
- 10
  Solder a nine volt battery clip to the PCB. Insert a nine volt battery and test the bug detector.

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