FM Transmitter Circuit 2n2218, this small transmitter can reach over 1 km in favorable broadcast conditions. Modulation can be done either with a microphone, by an electret microphone, or another audio source. The frequency is given by CV (common 5-20 or 6-30pF trimmer) and L1 4 or 5 turns of 22 AWG enameled wire, 1 cm diameter with an air core.
Pay attention to the capacitors, which should be ceramic. The antenna should be 72 cm long.
For transmission turn on a nearby FM receiver (radio) at half volume on a free frequency (that there is no radio operating), with a wood/plastic key, turn the CV screw until the strongest signal from the transmitter is picked up, as a spurious signal may be picked up.
If you have trouble adjusting, remove the coil and wind it again with more, or fewer coils.
Below is the circuit diagram of the FM transmitter. Pay attention to the 2n2218 transistor pinning.
Mic1 is a two-terminal electret microphone. Resistor R1 polarizes the microphone, you may need to change the value of R1 to adapt to your microphone, values from 1k to 10k can be tested.
Preferably use a fiberglass plate, being suitable for high frequency.
Schematic for assembling the FM transmitter with 2n2218
Suggested PCB for mounting the FM transmitter circuit
List of Material for assembly of the FM transmitter
Resistors 5% 1/4 w:
R1 = 10 kΩ Brown, black, orange, gold
R2 = 6.8 kΩ Blue, Gray, red, gold
R3 = 4.7 kΩ yellow, violet, red, gold
R4 = 39 Ω Orange, White, black, gold.
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C1,C3 = 100nF (104) Ceramic
C2= 6.8nF (682) ceramic
C4 = 6.8pF (6p8) ceramic
C5 = 10pF (10p) ceramic
C6 = 10µF/16V — Electrolytic
CV = TRIMMER 3-30 PF.
T1 = 2n2218, 2n2219 or equivalent.
L1 = see the text
B1 = 9V battery.
Mic1 = electret microphone.
Various = printed circuit board PCB, antenna, box, etc.
Pinout transistor 2N2218
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