Easy FM Tracking Transmitter

This is an easy FM tracking transmitter circuit project :). The scheme designed by Tony van Roon, and here the FM transmitter tracker diagram:

easy FM tracking transmitter

Components List:
R1 = 10K
C1 = 100uF/10V
C2 = 10nF
C3 = 4-40pF trimmer capacitor
C4 = 4.7pF
IC1 = LM3909
Q1 = 2N3904 NPN transistor
LED1 = Red LED/or another color as you like
L1 = 0.1uH, 6 to 8 turns of 22 gauge hookup wire close wound around a 1/4″ diameter non conductive core, such as a pencil
Antenna = 10 to 12 inches of hookup wire


  • For the purpose of stability, work with a NPO types for C2 & C4.
  • Resistance tolerance for R1 have to be 1 or 2% (use metalfilm resistor).
  • The coil is built from 22 ga ‘hookup’ wire, just like the solid Bell phone wire. Leave the insulation on.
  • Frequency range will be the usual 87-109Mhz on the FM dial.
  • The LED is the ‘High Brightness’ type for optimum illumination.

The current draw for this FM tracker is 3.7mA, so the 1.5V button cell will last a while. When your circuit is working you should see the LED flash quite fast. Take your FM radio and search for the low-beat ‘thumpe-thumpe-thumpe-etc’ equal to the flash of the LED (probably around the 100Mhz). Found it? If that position is interferering with a radio station you can fine-tune it with the variable capacitor. If you like to have the tracker around the 88Mhz you can do that by spreading the windings from the home-made coil just a bit (1/2 a millimeter or so). Well, have fun with it and find out. It is a good project. The 12-inch antenna can be anything, it’s not seriously that crucial. I made use of a piece of 22 gauge flexible wire.

One thought on “Easy FM Tracking Transmitter

  1. vasea

    ?????? ??????? ???? ?? ?????? ?? ????? ????????? ?? ???????? ???? ?? ????? ????? ??????? ?????? ??? ?? ????? vasea.nichita@mael.ry ???

Leave a Reply

Your email address will not be published. Required fields are marked *