FM Telephone Bug

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FM Telephone Bug

Post by Hertz on Thu Aug 19, 2010 9:44 pm

Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio. The frequency can be tuned from 88 to about 94Mhz and the range
is about 200 feet. It is extremely easy to build and is therefore a
good, useful beginner project.



R1 = 180 Ohm 1/4 W Resistor

R2 = 12K 1/4 W Resistor

C1 = 330pF Capacitor

C2 = 12pF Capacitor

C3 = 471pF Capacitor

C4 = 22pF Capacitor

Q1 = 2SA933 Transistor

D1, D2, D3, D4 = 1SS119 Silicon Diode

D5 = Red LED

S1 = SPDT Switch

L1 = Tuning Coil


1. L1 is 7 turns of 22 AWG wire wound on a 9/64 drill bit. You may need to experiment with the number of turns.
2. By stretching and compressing the coils of L1, you can change the frequency of the transmitter. The min frequency is about 88 Mhz, while
the max frequency is around 94 Mhz.
3. The green wire from the phone line goes to IN1. The red wire from the phone line goes to IN2. The green wire from OUT1 goes to the phone(s), as well as the red
wire from OUT2.
4. The antenna is a piece of thin (22 AWG) wire about 5 inches long.
5. All capacitors are rated for 250V or greater.
6. The transmitter is powered by the phone line and is on only when the phone is in use. S1 can be used to turn the transmitter off if it is not
7. If you have problems with the LED burning out, then add a 300 ohm 1/4W resistor in series with it.


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Join date : 2010-08-12
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Re: FM Telephone Bug

Post by jhon martinez on Tue Jan 24, 2012 12:39 pm

sir tanong lng po meroon ka bang circuit 2kilomers na fm transmeter jan.ung dito lng sa atin na bibili ung mga transistor

jhon martinez
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