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Project Notes

#208 FM/SingleStageTransmitterKit

Build a simple single-stage FK702 FM Transmitter Kit by Future Kit.

The Build

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

About LEAP#208 RadioFMTransmitter
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.