One Transistor Transmitter Test example - jontio/JMPX GitHub Wiki

Aim

Use a simple one transistor FM transmitter with JMPX to see what happens.

This was my experiment of using a simple one transistor FM transmitter. I do have 2 PLL FM modulators but wanted to demonstrate that even a horrid one transistor FM transmitter could at least demonstrate that JMPX will work with these kinds of transmitters at a pinch.

Design

I created the following oscillator as the transmitter.

This is different from any other FM transmitter oscillator I've made which is why I tried it. The input is the base of the transistor. You can if you want take some power from the emitter. The signal at the emitter is the following.

The build looked like the following

Results

Like all non PLL transmitters it drifted a lot and I had to be careful not to change the stray capacitance by moving anything. I ran it off a 3 cell LiPo (about 11v). With a bit of tweaking I got it oscillating around 90MHz when plugged into the soundcard. My white phone was fussy about transmitting exactly on frequency and if it was slightly off the sound volume would drop to a low level, my other phone without RDS did not have such a problem. The sound quality was ok. The figure below shows the RDS signal coming through to my white cell phone's radio.

Suggestions

Due to the drift this is not a practical transmitter but can be used to try out JMPX. Searching the Net for any "Simple FM transmitter schematic" will return a plethora of simple transmitters like this one and all should work with JMPX. Some may be better than others but I can't recommend any one over any other.