Cool Low Power Spy Mini-Transmitter
This circuit schematic is for a bare bones short range FM low power transmitter. The circuit operates on the commercial FM frequency band between 88 and 108 MHz. The input Audio from the electret microphone causes a shift in the resonant frequency of the Colpitts oscillator formed by the Q1 circuit. The frequency modulated signal is tapped off by the antenna which transmits the signal.
How Far Will it Go?
The circuit may be built on a proto board, perf board or printed circuit board. The reception range is limited and is dependent on both the environment and receiver. To extend the range I would recommend adding an output amplifier stage. Also, FM receivers like those in car radios which contain an RF preamp can improve the reception range.
Tweaking the Freq.
It may take some tweaking to find a clear spot on the FM band for best reception. The setting of variable capacitor and the coil spacing are critical in adjusting the resonant frequency of the transmitter. Feel free to leave a question, comment and/or suggestion. Thanks for reading this post.
