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1.5 Volt Tracking Transmitter
o For stability, use a NPO types for C2 & C4.
o Resistance tolerance for R1 should be 1 or 2%.
o Frequency range is the usual 87-109Mhz on the FM dial.
o The coil is made from 22 ga 'hookup' wire, like the solid Bell phone wire. Leave the
insulation on.
o The LED is the 'High Brightness' type for maximum illumination.
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. Have fun with it. --Tony.
