A friend of mine and myself are working on a computer controlled aircraft. Its basically a trainer that will be controlled via laptop and send back gyro information on the axis.

The main obstacle so far seems the FM Dual Conversion system. Can anyone offer me some help or information on how I would go abouts working a system that is fed information through the serial port.

So far I understand that the radio sends the commands through 2ms pulses in approximately 20ms frames. OK, great.

I also understand the ON position is given by a 5kHz shift in frequency (down for Futaba) and a 3.3v level.

The part i get confused on is this.

In FM, since the signal is always being sent as either original or 5kHz modulated, when does the voltage change, or is it always 3.3 volts?

Also, this dual conversion is really confusing! I've read the site !QUOT!Everything You NEVER Wanted to Know About Radios!QUOT! and it helped a lot, but I am still struggling with the dual conversion.

Additionally, does anyone know how to build a transmitter for this purpose that will connect to the computer? I understand the principle of FM, but what is the practice that actually makes it work? How does the frequency change? does it just broadcast on another freq. using a different crystal? Could someone offer some clarification on this?

Finally, I understand this is a weird and complicated job and I've asked about a million (exaggeration) questions in this post... so if you have information or links or connections to people with info on any of these topics or any of _these_ topics...

<edit></edit> After reading this, read the third post to perhaps understand me clearly. I don't think this makes too much sense as it stands right now information about the following topics or the third post would be appreciated, thanks! [[ Tuesday November 25 20003]]

radio protocols

FM protocols

how to make an FM transmitter from computer

dual conversion

how to make something that will transmit equivalent to my FUTABA Skysport 4, Dual Conversion 72.870MHz transmitter,


I'd be absolutely greatful!

Thank you very much