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

This is the schematic of the phone transmitter

Parts

Part
Total Qty.
Description
Substitutions
R11180 Ohm 1/4 W Resistor
R2112K 1/4 W Resistor
C11330pF Capacitor
C2112pF Capacitor
C31471pF Capacitor
C4122pF Capacitor
Q112SA933 Transistor
D1, D2, D3, D441SS119 Silicon Diode
D51Red LED
S11SPDT Switch
L11Tuning Coil
MISC1Wire, Circuit Board

Notes

  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 needed.
  7. If you have problems with the LED burning out, then add a 300 ohm 1/4W resistor in series with it.

Related Circuits

Ringing Phone Light Flasher, Phone Busy Indicator, FM Telephone Bug, Cut Phone Line Detector, Simple Phone Tap, Telephone Hold Button, Telephone Recorder, Remote Telephone Ringer

Comments

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Foolshatch
FM Telephone Bug
Thursday, May 10, 2012 9:23:19 PM
Nice. Actually its always good to have some elementary mistakes in schematic. So it will dump these fools around here who want to make all fast / grap/rip for their university courses and have no patience. Its very hilarious about led and switch and gurus can laugh later when the fools around here comment what happened with them or cant make it work... :D :D
Spork
FM Telephone Bug
Sunday, August 15, 2010 2:14:51 PM
For those asking why there's two inputs and two outputs, in the states, when you rip apart a phone line, you'll notice 4 wires. Two of these wires are generally not used. Once you splice the wire, instead of having one main telephone wire, you'll have two. The telephone wire that goes to the source (outside), is IN. The one that goes to the telephone, is OUT. You take the two wires inside of the IN main telephone wire and put it in IN1 and IN2 respectively. Then you do the same for the OUT1 and OUT2 but with the main line that goes to the telephone.
anonymous
FM Telephone Bug
Tuesday, July 27, 2010 11:24:57 AM
could someone please suggest an equivalent diode, mabye one that is more common, to use? i cant seem to find the "1SS119 Silicon Diode". also a link to a site where they sell this diode or a similar one would be great.
WICKED
FM Telephone Bug
Wednesday, June 16, 2010 11:30:56 PM
is the oscillator Q1, C2, C4, L1, R2, R1, and C1
Riaz
FM Telephone Bug
Wednesday, June 16, 2010 12:45:33 AM
I made this circuit as a project for telecommunications class. It works well and is fairly easy to assemble. yes, capacitors can be a little different than shown above (using a 10pf cap instead of a 13pf, for example). Two notes: Switch is useless in this schematic, as it would simply separate the phone line from the rest, so you can just eliminate it. You can also get rid of the LED (there is absolutely no point in having a bug with a light). For the connections, here is a image of how to connect: http://img689.imageshack.us/img689/2186/bugconnect.png . This circuit does not care which side of the connection is in and which is out. If built compactly can easily fit inside a small phone box. Good luck, and have fun! btw, why silicon diodes? germanium work just as well as far as i can see!
9A3HP
FM Telephone Bug
Tuesday, May 25, 2010 6:51:28 AM
http://www.postimage.org/image.php?v=PqFJ_Or switch must be connected between IN2 and OUT2 when switch is close, bug is off, if switch open bug is on. 470 and 471 pF same work well , any 1N4xxx will be same , how connected IN1 and IN2 to phone line, OUT1 and OUT2 to telephone device, simple ?
anonymous
FM Telephone Bug
Saturday, March 20, 2010 6:38:00 PM
I can't seem to find a 471pF capacitor, but i suppose i can use a 470 pF?
anonymous
FM Telephone Bug
Saturday, February 06, 2010 5:21:45 AM
how do we connect circuit to the phone line because we have two inputs and two outputs?
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
keanhong2
FM Telephone Bug
Monday, May 05, 2008 11:11:04 AM
question 1)the diode 1ss119 silicon diode can replace wait what other similar to these diode ? 2)transistor 2sa933 got other replacement ??
crrimson
FM Telephone Bug - Circuit works!
Monday, April 28, 2008 11:47:25 PM
This is the first FM transmitter I've gotten to work, and it was pretty easy to build, it works great! Thank you. For anyone trying to build it, I used a BC557 transistor for Q1, and 1N4002 for D1-D4 instead since I couldn't find the parts it asked for.
Kyle
FM Telephone Bug
Tuesday, April 22, 2008 12:03:52 PM
Where can I buy a 1SS119 Silicon Transistor? Or is there something else that can be substituted? Thanks!
anonymous
FM Telephone Bug
Monday, April 07, 2008 12:04:06 PM
Is there a circuit that can be used to detect this bug or any other bug for that matter? If there is, can you please send it to me together with its description.
anonymous
FM Telephone Bug
Wednesday, March 26, 2008 7:58:35 PM
How could you switch it to an audio jack input like in a mp3 player?
anonymous
FM Telephone Bug
Wednesday, March 12, 2008 8:43:03 PM
How could you switch it to an audio jack input like in a mp3 player?
Michael
FM Telephone Bug
Wednesday, March 12, 2008 3:12:31 PM
How I can substitute the tuning coil with a adjustable capacitor (if I can)?
pratik
FM Telephone Bug
Friday, February 29, 2008 10:00:07 AM
how do I connect this circuit to the telephone line in parallel
phani
FM Telephone Bug
Tuesday, January 22, 2008 3:19:29 AM
we are interested in doing this project. can you please send the other diodes which can do the same function as that of 1SS119-sillicon diode .also for the transistor 2SA933
hulu beliku
FM Telephone Bug
Wednesday, January 16, 2008 3:39:55 AM
how do i connect circuit, parallal to the phone line?
hulu beliku
FM Telephone Bug
Wednesday, January 16, 2008 3:34:03 AM
To wind the turns of a coil it says to use 22 AWG wire wound on a 9/64 drill bit.So what does it mean by 9/64 drill bit. would you tell me in centimeter? and 22 AWG would you tell me also this in mm?
anonymous
FM Telephone Bug
Tuesday, December 18, 2007 4:04:23 PM
i think the frequency is something to do with one of the resistors i cant remember tho havnt got to radio systems in electronice gcse yet
SNIPES
FM Telephone Bug
Saturday, October 27, 2007 11:36:41 PM
I DO APPRECIATE MUCH THE CIRCUIT THAT YOU HAVE PUBLISH IN THE NET IN FACT I AM USING IT RIGHT NOW IT PERFORM VERY WELL THAT FOR THAT,MORE SIMPLE GADGET IN THE FUTURE
lenny H
FM Telephone Bug
Thursday, September 20, 2007 3:49:28 PM
You sure about the wiring of S1? Is C3 meant to be 470pF?
Ntokozo
FM Telephone Bug
Thursday, September 20, 2007 6:35:42 AM
Is there a circuit that can be used to detect this bug or any other bug for that matter? If there is, can you please send it to me together with its description.
anonymous
FM Telephone Bug
Sunday, September 16, 2007 11:05:33 AM
is there anyway wher ei can set the freqency
Brea
FM Telephone Bug
Monday, September 03, 2007 10:16:41 PM
This is a really good site, i love it but how exactly do you connect the device to the telephone line?
snipes
FM Telephone Bug
Sunday, August 26, 2007 10:11:54 AM
i've just finished fm telephone bug it's great it's functioning thank you very much i just like to ask a PCB circuit of this in order to make it as small as possible thank very much i appreciated this project good luck!!!....
snipes
FM Telephone Bug
Saturday, August 25, 2007 10:58:58 PM
sir what a nice circuit can you send me a PCB design of this?it will be much appreciated here in our country Philippines.
pherus
FM Telephone Bug
Wednesday, August 22, 2007 10:27:36 AM
Hi Aaroncake, I would like to know about the procedures in assembling the fm telephone bug and also how to troubleshoot the bug.
nivaz
FM Telephone Bug
Saturday, August 11, 2007 7:00:55 AM
sir,this is a nice one.............can u please send me the proforma of the project...the project details..
khuram
voice changer
Saturday, August 04, 2007 5:56:40 PM
sir,plz send me voice changer circuit diagram for mobil & phone set.phone bug circuit has v.good result.
moeen
request
Monday, June 04, 2007 2:37:20 AM
sir.. it will be so nice of u if u kindly send me some more details of this circuit. its really good. hoping to hear from u soon bye tc
Ravi
FM Telephone Bug
Tuesday, May 29, 2007 10:37:46 AM
I lyk this ckt very much,
alifoow
Telecomm
Thursday, May 24, 2007 7:35:17 AM
hey i need to help my project am final year after one semester i will do my project so any one can help me the previews telecommunication projects wish some1 knws i'll be waiting soon
john
FM Telephone Bug
Wednesday, May 23, 2007 1:58:21 AM
My telephone line does not change polarity when the call is on. You are telling that telephone line changes when a call is active that how shall i use this transmitter
Dr Quest
FM Telephone Bug
Tuesday, May 22, 2007 9:55:08 PM
I like to listen to internet talk radio and I wondered if I could use just my phone line to transmit a signal to a FM radio to my back yard, as long as my phone is off the hook and close to the computer speaker.
daniel
FM Telephone Bug
Sunday, May 20, 2007 7:18:59 AM
could you please give me some information on the actual working of the circuit above (as in what kind of oscillator and the telephone standard used etc) or suggest some sites that would help me understand it better?
Llamarama
FM Telephone Bug
Saturday, May 05, 2007 5:14:43 PM
MM: you could use 1N400x diodes instead of 1SS119s. It worked for me! This is a good project!
Stephen
FM Telephone Bug
Thursday, May 03, 2007 6:09:21 PM
I have multisim 10, and was wondering how do I simulate a phone line in multisim? my email is
Sibin
FM Telephone Bug
Saturday, April 28, 2007 11:43:22 AM
Plzzzzzzzzzz tell me iam a begineer how to connect the telephone wires
talew
FM Telephone Bug
Thursday, April 26, 2007 9:32:39 AM
all abaut the fm telephone bug and where it is applicable tell me references additional notes to your project thank more!
talew
FM Telephone Bug
Thursday, April 26, 2007 9:27:58 AM
SPDT Switch for what purpose is use tell me soon we are bigener engineer
emme
FM Telephone Bug
Saturday, April 21, 2007 6:50:04 AM
how can I replace SPDT switch
kquick
FM Telephone Bug
Thursday, April 19, 2007 5:24:42 PM
did u use the yellow n black wires. if so where are they connected??
nitin
FM Telephone Bug
Thursday, March 29, 2007 6:26:05 AM
i like it .
MM
FM Telephone Bug help
Saturday, March 17, 2007 11:09:22 PM
I can't find the 1SS119 diode what can i replace it with and can i wound L1 on 9/64 steel nail Thanks for ur time
Asad
FM Telephone Bug
Thursday, March 15, 2007 5:36:52 AM
may be its a good and useful circuit. but in this kind of rf broadcasting device how we can controll the unauthorize access. its range is 200 feet and if your neighbur is also playing with a radio set then he can also receive your telephonce bug voice... pls reply
John
FM Telephone Bug
Monday, March 12, 2007 7:24:53 PM
Nice i really like this thanx
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