FM Telephone Bug

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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.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	180 Ohm 1/4 W Resistor
R2	1	12K 1/4 W Resistor
C1	1	330pF Capacitor
C2	1	12pF Capacitor
C3	1	471pF Capacitor
C4	1	22pF Capacitor
Q1	1	2SA933 Transistor
D1, D2, D3, D4	4	1SS119 Silicon Diode
D5	1	Red LED
S1	1	SPDT Switch
L1	1	Tuning Coil
MISC	1	Wire, Circuit Board

Notes

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.

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.

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.

The antenna is a piece of thin (22 AWG) wire about 5 inches long.

All capacitors are rated for 250V or greater.

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 needed.

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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Comments

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9A3HP FM Telephone Bug Thursday, October 22, 2009 1:36:03 PM

I see previous this schematic diagram and same error occurs in any possible web sites , the switch is wrong placed in schema. Switch must cutoff bug from telephone line and close contacts that IN2 and OUT2 short between. This only have logic. No hard feeling.

siva FM Telephone Bug Thursday, September 03, 2009 1:15:37 PM

we are highly interested in doing this as our semester project. But we are facing difficulties understanding this circuit as it has 2 inputs and 2 outputs. Kindly send us details in this regard and if u could send us report we will be highly thankful....

Mart FM Telephone Bug Thursday, February 26, 2009 6:30:07 AM

Shouldn't the switch S1 trigger between IN2 > schematic and IN2 > OUT2? Otherwise, doesn't it break the phone line?

Malik Naveed Zafar HELP.... Wednesday, December 31, 2008 1:32:48 AM

we are highly interested in doing this as our semester project. But we are facing difficulties understanding this circuit as it has 2 inputs and 2 outputs. Kindly send us details in this regard and if u could send us report we will be highly thankful....

dharmendra chauhan FM Telephone Bug Wednesday, October 22, 2008 2:49:40 AM

it is good for me...........i foud this type of project such a long time..........i need a hoby project for my EDC,..plz send me this kind pjt on my mail... thank u

Ravish FM Telephone Bug Wednesday, October 15, 2008 2:02:12 PM

Thanks for giving this wonderful circuit....... Will you please explain this circuit properly & how could i extend the range???? And one wonderful thing i found is that we can use 1N4007 diodes in place of 1SS119...

Gaz FM Telephone Bug Thursday, September 11, 2008 7:05:53 PM

Please can you advise me on where to buy 1SS119 Silicon Diodes, Thanks!

getnet zewde FM Telephone Bug Saturday, August 23, 2008 4:02:30 AM

thise ckt is legale no probelemfor tell

anonymous FM Telephone Bug Tuesday, June 10, 2008 10:27:14 AM

We are interested in ding this project can you please help us how do we connect circuit to the phone line becouse we have two inputs and two outputs.

swadjaya FM Telephone Bug Sunday, June 01, 2008 4:38:02 AM

I need information about 1SS119 Silicon Diode substitution because I can't find this item in Indonesia. Thank's

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9A3HP	FM Telephone Bug	Thursday, October 22, 2009 1:36:03 PM
I see previous this schematic diagram and same error occurs in any possible web sites , the switch is wrong placed in schema. Switch must cutoff bug from telephone line and close contacts that IN2 and OUT2 short between. This only have logic. No hard feeling.
siva	FM Telephone Bug	Thursday, September 03, 2009 1:15:37 PM
we are highly interested in doing this as our semester project. But we are facing difficulties understanding this circuit as it has 2 inputs and 2 outputs. Kindly send us details in this regard and if u could send us report we will be highly thankful....
Mart	FM Telephone Bug	Thursday, February 26, 2009 6:30:07 AM
Shouldn't the switch S1 trigger between IN2 > schematic and IN2 > OUT2? Otherwise, doesn't it break the phone line?
Malik Naveed Zafar	HELP....	Wednesday, December 31, 2008 1:32:48 AM
we are highly interested in doing this as our semester project. But we are facing difficulties understanding this circuit as it has 2 inputs and 2 outputs. Kindly send us details in this regard and if u could send us report we will be highly thankful....
dharmendra chauhan	FM Telephone Bug	Wednesday, October 22, 2008 2:49:40 AM
it is good for me...........i foud this type of project such a long time..........i need a hoby project for my EDC,..plz send me this kind pjt on my mail... thank u
Ravish	FM Telephone Bug	Wednesday, October 15, 2008 2:02:12 PM
Thanks for giving this wonderful circuit....... Will you please explain this circuit properly & how could i extend the range???? And one wonderful thing i found is that we can use 1N4007 diodes in place of 1SS119...
Gaz	FM Telephone Bug	Thursday, September 11, 2008 7:05:53 PM
Please can you advise me on where to buy 1SS119 Silicon Diodes, Thanks!
getnet zewde	FM Telephone Bug	Saturday, August 23, 2008 4:02:30 AM
thise ckt is legale no probelemfor tell
anonymous	FM Telephone Bug	Tuesday, June 10, 2008 10:27:14 AM
We are interested in ding this project can you please help us how do we connect circuit to the phone line becouse we have two inputs and two outputs.
swadjaya	FM Telephone Bug	Sunday, June 01, 2008 4:38:02 AM
I need information about 1SS119 Silicon Diode substitution because I can't find this item in Indonesia. Thank's