At times many of you must have felt the need of spying on some body’s conversation over the telephone and wondered how to bug a telephone.
Morally it won’t be correct to eavesdrop on an individual’s personal discussion, but through electronics you can always and every time find a way of fulfilling your wishes no matter whether the act is ethical or not.
Though I won’t recommend using the present circuit for listening to somebody’s private talks, it can rather be used as a fun gadget for broadcasting a telephone conversation over the FM radio.
The circuit is very simple to build, so tiny in size that it easily fits inside the landline telephone itself. Once connected to the wires of the telephone line, it will immediately detect any conversation made over the particular telephone and convert them into FM signals. By carefully tuning your FM set, you should be able to listen to these speech signals wirelessly up to a radial distance of more than 10 meters.
The out put is distinctly clear and the listener should be able to hear even the whispers of the person conversing over the telephone.
It can also be used to record a conversation made over a telephone. So if you are thinking how to record a telephone conversation? The idea is simple. The signals aired from the circuit may be received by the FM radio of your mobile phone and easily recorded.
About the Circuit
The functioning of the circuit may be understood through the following step wise explanation:
- The circuit is basically a single transistor oscillator, which oscillates at a frequency of around 100 MHz.
- Transistor T1 along with the associated capacitors and the inductor forms a high frequency FM signal generator.
- The sound signals in the form of electrical pulses passes through the capacitor C1 and reaches the base of the transistor T1.
- These electrical pulses are modulated over the 100 MHz carrier signals and are transmitted in the air through the antenna coil L1.
- The transmitted electrical pulses are captured by the FM receiver and are converted back to speech vibrations through its speakers, and thus we are able to hear the telephone conversation over the FM radio.
- The unit does not require an external supply voltage to operate as this is derived from the telephone line itself. Since its current consumption is negligibly low, you don’t have to worry regarding its effect on your telephone bill.
You will require the following electronic components for its construction:
- Resistors: 1 K, 82 K, 68 K one each (all are ¼ watt, CFR),
- Capacitors: 103/100V PPC, 82 pF, 10 pF, 27 pF, 100/25 V one each,
- Rectifier Diode: 1N4007,
- Zener Diode: 4.7 V, 400 mW,
- Coil: 4 Turns of 21 SWG super enameled copper wire, 4 mm in diameter.
How to Build and Bug it in a Telephone?
The construction of this circuit may be carried in the following manner:
- With the help of the circuit schematic construct the circuit over a piece of general PCB, try to keep the components perfectly organized so that the whole unit becomes very compact in size.
- Join two small lengths of wire to the circuit as supply inputs. Also do not forget to connect a 10 inches antenna wire to the circuit.
- Wrap the circuit completely with plastic PVC tape to insulate it from any possible short circuit.
- Now it is ready to be bugged inside a telephone. If you don’t want to disturb the telephone instrument, the device may also be easily accommodated inside the telephone distribution box.
- Unscrew the box; connect the circuits supply wires in parallel to the input telephone wires. Squeeze out the antenna wire through a suitable outlet and let it hang outside. Fix the cover of the box back into its place.
- This concludes the “bugging” procedure. Switch ON a FM radio and start tuning it. You should be able to get a null spot, where the “hissing” of the radio completely vanishes.
- Now pick up the handset of the telephone from the cradle and instantly you should hear its dial tone over the radio loud and clear. Similarly, now every call made here will be audible in your FM radio on the particular wavelength.
Now since that you know how to bug a telephone, hopefully you will use it for a healthier purpose.
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Image courtesy: https://techylife.com/cell-phone-tapping/