Introduction:

The following plans describe how to build a very small tracking transmitter that can be tracked using an FM broadcast band radio receiver. The transmitter is powered by a 3 volt to 9 volt battery and has a range of from 1/4 mile to over 1 mile depending on battery voltage, height above ground, receiver sensitivity, and antenna length. The circuit's size including the batteries is 3/4" by 1 3/4" when powered by two 3volt lithium batteries and twice that size when powered by a 9 volt transistor radio battery. A skilled technician can reduce the size considerably by packing the components tighter on the circuit board. This circuit is ideal for use as a beacon on cars and boats and can even be flown in small model rockets.

The transmitter requires patience and a steady hand to tune and it's frequency is prone to drift. Consequently, it is recommended that it be used with FM radios that can tune continuously across the frequency spectrum. That said, the transmitter is cheap to build, can be built from readily available parts, does not require any expensive test equipment, works well with cheap pocket FM receivers, and can be built by hobbyists with moderate soldering skills provided they don't try to make it too small.

The plans include a parts list, parts sources, schematic diagram, and recommended parts layout for perfboard construction

Theory of operations:

Please refer to the circuit schematic when reading the following description.

The transmitter is composed of three smaller circuits; A transmitter, an audio oscillator and a circuit that pulses the tone oscillator and transmitter on and off.

The transmitter is a variation of a very common FM oscillator circuit that is extensively used in circuits of this type. It consists of one transistor (T2) whose oscillation is determined by a parallel resonance circuit composed of C5 and L1. C6 provides the feedback needed for the oscillation and ca

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