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#208 FM/SingleStageTransmitterKit

Build a simple single-stage FM Transmitter Kit

The Build

▶️ return to the LEAP Catalog

Notes

I've been experimenting with FM, and the hardest thing to get right tends to be the hand-wound coils. So to get a baseline, I picked up a 1-transistor kit during a recent visit to Sim Lim Tower.

The kit is the FK702 by Future Kit. It takes the hastle out of getting the LC circuit right by printing the inductor coil on the PCB (used in conjuction with a trimmer capacitor).

Power Connections

The PCB includes +9V and GND connectors.

Optional Transmit-enable switch

The PCB includes connections for an optional transmit switch (not included). I put a switch in my build.

Performance

tl;dr: Not that great!

With the supplied coil antenna, I don't get much more than a metre range before the signal is lost to noise.

Adding 30cm rabbit ears gives about 5m.

Frequency is quite selective which is good, but stability is a bit all over the place - it will drift and jump over time.

Here's a trace of the signal and FFT when tuned at 83.25MHz:

scope_signal

scope_fft

Construction

Breadboard

The Schematic

The Build

Credits and References