The most important part of this 88-108 transmitter is the Colpitts oscillator. C3,C4,C5,C6,CD1-CD2 ans L1 determine the transmission frequency. The RF Oscillator circuit has the BF982 MosFet transistor wich is the active part. The others 2 transistors separate the VCO from antenna.


The first stage BF199 amplifies the weak signal from the vco and functions in constant load. The second stage BFR90 amplifies the rf signal to load the antenna wich will radiate the radio frequency power.
Antenna can be one wire, 70 cm long. L1 coil has 1mm thick copper wire, 3.5 turns, 5 mm diameter and 1mm space between turns.
You can use BF199 instead of BFR90 and MV104 instead of the 2 varicape diodes.

FM transmitter circuit diagram

fm transmitter schematic bfr90 300x116

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