This FM transmitter circuit is a quite fun project for electronics beginners, so here’s a circuit with the 2SC9018 transistor. It uses the 2SC9018 high frequency transistor, based on a different spin of the common base Collpit’s oscillator. The circuit is rather simple, uses only one transistor and few passive components and performs well in terms of frequency stability, almost zero drifting after about 4 hours of continuous operation.
Here the RF feedback is taken from the centre tap of C2 and C3, close to original Collpit’s oscillator.
You can calculate the effective capacitance of the tuned LC circuit by determining the series capacitance of C2 and C3.
If both C2 and C3 are equal, the effective capacitance will be the half.
FM transmitter circuit Part list and construction
Q1 – C9018 NPN transistor
R1 – 470 Ohm, 1/4 watt
R2 – 10 kOhm, 1/4 watt
C1 – 2.2 nF ceramic disc capacitor (222)
C2 – 30 pF ceramic disc capacitor, (30)
C3 – 30 pF ceramic disc capacitor, (30)
C4 – 10 pF 30 pF ceramic disc capacitor, (10)
C5 – 1 nF 30 pF ceramic disc capacitor, (102)
C6 – 100nF 30 pF ceramic disc capacitor, (104)
L1 – 16 turn on 3 mm diameter
This circuit uses only 10 parts including the coil.
The coil is winded on a 3 mm drill bit, 16 turns of 0.4 mm (28 S.W.G) enamelled copper wire.
It’s very easy to construct the circuit on a strip board, just few components to solder. Always try to minimise the track length.
My prototype without the audio source connected, small enough to fit on a matchbox. Fix the inductor with some wax for better frequency stability.
This circuit runs on a 3.3 Volt regulated power supply.
So, that’s all for this FM transmitter circuit project, if you have any suggestion or question, just drop a comment.