A great low power FM transmitter

Saw this little FM transmitter for the broadcast band on the Make Blog.

I often want to listen to the Sunday ham radio broadcast but it would be great to not have to sit by the rig for the whole duration so I've used an iPod FM transmitter to relay the audio but they have very short range, even with an antenna added.

Turned out I had all the required components in my junk box. Built the oscillator first and it just worked right off, then built the buffer stage.

This circuit has an RF buffer stage so touching the antenna won't pull it off frequency. Running on a 9V battery it puts out enough power to cover the house. It's getting hard to find a spare frequency but I put it down near 88Mhz and it works very nicely.

I really love the aesthetic of "ugly" construction and it's so quick to throw together these little projects. I did release the smoke on the buffer transistor by accidentally using a 1K bias resistor in place of the 100K but after a small explosion that was fixed.

This design is to be recommended, it worked without any problems (except those of my own making) for me other than a bit of stretching of the oscillator coil to get it on band and it seems exceptionally stable given the construction.

If you tap the board it transmits a lovely metallic "clang" sound from the coil but that's to be expected.

I remember many years ago building JostyKit transmitters which had the coil etched onto the circuit board.