My Electronics Hobby: Telephone FM Transmitter

Thursday, April 20, 2006

Telephone FM Transmitter

Posted by LeorickSimon at 12:04 AM

Descrition & Circuit

This project is taken from www.electronics-lab.com.
With some modification, I create my own version of FM Telephone bug complete with stripboard layout.
Theortically, the frequency range is from 88MHz to 94MHz but you may experiment with the coil structure to tune it

Circuit

Strip Board Layout

Parts List

Diode	IN4384	4
	LED	1
Resistor	12k	1
	1k	1
	200R	1
Capacitor	470p	1
	330p	1
	25p	1
	12p	1
Transistor	A933(PNP)	1
Coil	*See note	1

*Coil note
7 or 8 turns of 22AWG(diameter .6mm) around 9/64inch(3.6mm) drill bit. Antenna using the same wire 22AWG, 5inch long

Picture

Compact!	With antenna!
Put it online!	Get ready to tune your radio!

31 Comments:

fxtreme said...

Why can't you put this at
http://www.instructables.com/

Sounds like a decent project
http://vinodvv.wordpress.com

03 May, 2006 09:37

Bob said...

Hey this is really cool! And thanks for the link to Electronics Lab I am going to check this out for sure.. //bob

04 May, 2006 14:48

Casa De Toad said...

Just like the CIA used to make in the good ole days

05 May, 2006 09:06

itwasashark said...

how far does it transmit

14 May, 2006 10:43

Abnormaltalent-bos said...

Hi your blog is nice. I found this site about Reverse Cell Phone Lookup, take a look at it some time.

21 November, 2006 14:15

robman78 said...

What is the purpose of this and what can be done with it - Newbie

29 December, 2006 04:46

LeorickSimon said...

Transmitting the telephone conversation to FM radio. (spy kit)

29 December, 2006 18:44

kquick said...

what is IN and OUT??

16 February, 2007 06:30

LeorickSimon said...

IN, to the telephone line (wall socket), OUT, to the telephone.
It doesn't matter actually. It just a pair label.

16 February, 2007 18:53

mohamed said...

Can any one tell me where can i find this wire cause i searched alot for itwith no success
Thanks alot.

03 April, 2007 10:37

LeorickSimon said...

This page should help.
Try to use a coil from old tv booster for example.
If you are not sure which wire to use, just measure the wire diameter using caliper or micrometer.
It should be around 6 mm in diamater.

03 April, 2007 19:27

vinita said...

how do we tune the coil?

19 April, 2007 22:47

johnygfunk said...

I understand the circuit fairly well but the phone line connections are a bit confusing. Phone lines have multiple wires and thus just two ins and two outs is a bit confusing. Anyone mind telling me what wires to connect from the wall to the circuit and from the circuit to the the bugged phone. It would be much appreciated.
fixed spelling errors

20 April, 2007 00:53

LeorickSimon said...

"how do we tune the coil?" From my experiment, the output carrier frequency depend on the coil form/structure such as the diameter of the core, how many turns, stretching and compressing the coil layers. This is what I mean by "tune the coil".

20 April, 2007 19:16

Shaunak said...

Hi,
I have a suggestion,
why not add a SPDT swich with one throw connection the above circuit and another shorted to the trird leg so that YOUR conversations can remain private. ;)

30 April, 2007 17:57

Anonymous said...

You set the transmit frequency by spreading or compressing the coil. This is a trial & error method and may take several tries at it before achieving the desired frequency. Once you are on the desired frequency, you can apply several drips of hot wax on the coil to stabilize the windings. However you may still encounter some frequency drift from such a simple circuit.

08 June, 2007 00:23

Anonymous said...

Sorry to sound stupid but what is the difference between the circuit and the schematic? Obviously they are different but what is the purpose of both?

01 September, 2007 22:55

Sue said...

Hey, I am a way beginner but I would love to learn how to make this. Does anyone know or is able to give me more indepth instructions about how to make this? You can email me at panasonic2522@yahoo.com anything would help! Thanks so much!

01 September, 2007 23:52

LeorickSimon said...

"Diff. between schematics and circuit",
I'm not sure about this.
Did you try to look at wikipedia (Schematics and Circuit_diagram) yet?
Any language expert here?

03 September, 2007 19:35

Sue said...

i meant the circuit and the stripboard, why are they different? Also how do i connect the phone line to the transmitter if i dont have that nifty little cream colored square that is shown in the picture?

04 September, 2007 04:18

LeorickSimon said...

I hope this may help. The circuit above is a simplified conventional pictorial representation of an electrical circuit. The strip board layout is the actual physical assembly layout of the transmitter it self. Click here see the side by side comparison image;

If you don't have a "little cream colored square", try to find a pair of RJ11 male and female like below;

RJ11 Male/Female image

04 September, 2007 21:31

Sue said...

oookay, i think im getting it! :) thanks so much! one more question: what wires go in the fm bug, where it says to phone and to wall, which out of the four wires in a phone line go where?

05 September, 2007 01:05

Anonymous said...

LeorickSimon said...
IN, to the telephone line (wall socket), OUT, to the telephone.
It doesn't matter actually. It just a pair label.
16 February, 2007 18:53

Connect the "OUT" end to the phone and
the center pair of your wall socket (red and green) to "IN" end.
(RJ-11 detail reference).

05 September, 2007 22:07

Martin said...

I recently built very cool stereo transmitter from this site http://electronics-diy.com/BA1404_Stereo_FM_Transmitter.php

This telephone transmitter is really small. Is it possible to use phone line as antenna?

14 September, 2007 11:05

BERK said...

hi i m interested in any kind of spy surveillance products and projects.İt can be anything like spyphone,phone spying,software or hardware,room bug,telephone related spy and surveillance devices,remote covert listening,micro recorders,spy gps devices etc.if anyone have any good idea or any project for sale just contact me please. http:www.sicaktakip.com

08 October, 2007 08:21

Alex said...

that sounds cool, if you find out any good ones would you let me know too?

13 October, 2007 04:15

sammy said...

Hey, can i buy a complete kit or assembled one from you? I tried to do it myself, but for some reason it's not working. U can email me at mrsamoo@gmail.com

29 October, 2007 10:08

sammy said...

To add to my comment above, Do u know if it can work with VOIP phones( phones through internet)?
Your comment will be appreciated.

30 October, 2007 05:40

Anonymous said...

What is the difference between SWG and AWG wire.

29 December, 2007 03:29

Anonymous said...

can you modify it even further and take out the transmitter part? i dont have the coil so im going to have to go with a tape recorder or a set of head phones.

15 April, 2008 08:02

LeorickSimon said...

If you are interested in wired version, you might wanna take a look here, Inductive Telephone Tap. You could plug it into a microphone input.

15 April, 2008 21:09