Friday, 3 February 2012

Mini FM transmitter (500mW - 1w) 88-108MHz VCO

Here is a little project i have been working on; A miniture FM transmitter (my favorite of all electronic fields RF!).

This transmitter puts out between 500mW and 1W (maybe more!). It runs off 12-15VDC and draws between 100 and 150mA.

Tuning is voltage controlled (using a variable capacitance diode (varicap) and a 10k 10 turn pot).

I've used 2 off MC120 type coils in series for the oscillator coil in a effort to minimise drift.

The borad was only a prototype and unfortunately i slightly misaligned the top copper layer which means it had to be cut by hand in place, still ,works ok. Because of it's prototype nature ground pins are soldered on both copper planes.

There is a single resistor and capacitor that are no longer required (i changed the design a little), there is also a small piece of ground plane i forgot to connect, and a low value ceramic capacitor i ahd to solder to the bottom of the PCB. There is a couple of surface mount components, one (the cap) i used through choice, the other (an inductor) was always designed to be SMA to save space.

All these errors have been corrected in the rev.2 PCB.

I used 4 off 220 ohm 1/2 watt resistors to make a 55 ohm dummyload (becasue i had a load of them laying around).

I may make kits available through ebay if there is any interest.