This project is a complete crystal-controlled Wide Band Frequency Modulated (WBFM) transmitter delivering a power output in the order of 10 milli-watts (+10dBm) using simple components. The transmitter is based upon the Phase-Locked Loop (PLL) principle, but due to the circuit's simplicity a true "phase lock" can never be achieved.
The transmitter has both 1v peak-to-peak 'LINE' input and 10mV 'MIC' audio inputs. These will accept audio input sources from external equipment, such as hi-fi, CD and computer equipment. The microphone input also has an in-built power source to energise an 'Electret' type condenser
microphone. The Radio Frequency (RF) output circuitry includes a three-pole filter for reduction of harmonics and other spurious signals. The spurious output signal level is better than -40dBc (0.0001 times the power of the wanted signal level), which makes the project suitable for driving an external power amplifier.The transmitter is powered from a 12v supply, but it will operate from 9 Volts to 16 Volts. The DC power input is equipped with a diode (D1), which protects the transmitter in the event the supply voltage is inadvertently connected the wrong way round.
Download Kit Intro Datasheet