FM Telephone Bug

Author Views Views Today Rank Comments
46,227 46 39
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

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?
The last 10 comments are currently shown. Show All Comments.

If you would like to leave a comment, you can do so using the form below. Comments can be things like suggestions, successes or failures, improvements, similar circuits, error reports, an answer to a previous commenter's question, or anything in between. However if you would like to ask a question it is suggested that you use the forum instead. The forum provides a more robust environment for discussion.

Important: If you post a technical question here, there is no guarantee it will be answered. All technical questions should be posted to the forum. The owner of this site generally does not answer questions in comments.

All comments are subject to approval before they are displayed here, so your comment will not appear immediately. This is done mainly to prevent spam and other abuse. If you wish to remain anonymous, simply enter "anonymous" for your name and/or email.

Name:
Email:
Subject:
Comments:
Anti Spam Code:
Please enter the exact text shown in the image above into the box below.
Browser cookies must be enabled to comment on circuits.

Privacy Policy

Back To Circuits Page | Mail Me | Search