FM Transmitter

Here is the schematic, PC board pattern, and parts placement for a low powered FM transmitter. The range of the transmitter when running at 9V is about 300 feet. Running it from 12V increases the range to about 400 feet. This transmitter should not be used as a room or telephone bug.

Schematic This is the schematic of the FM Transmitter

PC board layout and parts placement

This is the printed circuit layout and parts placement of the FM Transmitter

Parts:

C1_____________.001uf Disc Cap
C2_____________5.6pf Disc Cap
C3,C4__________10uf Electrolytic Cap
C5_____________3-18pf Adjustable Cap
R1_____________270 Ohm 1/8W Resistor
R2,R5,R6________4.7k 1/8W Resistor
R3_____________10k 1/8W Resistor
R4_____________100k 1/8W Resistor
Q1,Q2__________PNS2222A (or equlivelant) NPN Transistor
L1,L2___________5 Turn Air Core Coil
MIC____________Electret Microphone
MISC___________9V Battery Snap, PC Board, Wire For Antenna

Notes:

1. L1 and L2 are 5 turns of 28 AWG enamel coated magnet wire wound with a inside diameter of about 4mm. The inside of a ballpoint pen works well (the plastic tube that holds the ink). Remove the form after winding then install the coil on the circuit board, being careful not to bend it.

2. C5 is used for tuning. This transmitter operates on the normal broadcast frequencies (88-108MHz).

3. Q1 and Q2 can also be 2N3904 or something similar.

4. You can use 1/4 W resistors mounted vertically instead of 1/8 W resistors.

5. You may want to bypass the battery with a .01uf capacitor.

6. An antenna may not be required for operation.