The current draw for this tracker is 3.7mA, so the 1.5V button cell will last awhile. What the heck am I suppose to hear you ask? When your circuit is working you should see the LED flash quite fast. Take your FM radio and search for the low-beat 'humbe-humbe-humbe-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). Anyways, play with it and learn. It is a nice project. The 12-inch antenna can be anything, it is not really that critical. I used a piece of 22 gauge flexible wire. I haven't checked the range but will do that shortly.
- For stability, use a NPO types for C2 & C4.
- Resistance tolerance for R1 should be 1 or 2%.
- Frequency range is the usual 87-109Mhz on the FM dial.
- The coil is made from 22 ga 'hookup' wire, like the solid Bell phone wire. Leave the insulation on.
- The LED is the 'High Brightness' type for maximum illumination.
1.5 Volt Tracking Transmitter
The current draw for this tracker is 3.7mA, so the 1.5V button cell will last awhile. What the heck