I have a question about this, is it the new rc4 protocol you talk about or the old? And if it is the old what have you found out about?

Just opened it up and played around. I managed to track airplanes flying overhead. But I didn't see anything obvious in the spectrum analyzer or waterfall view.

That said I'm a total SDR newbie...

This thread has reached a milestone: 50,000 views! I would never have guessed that there would be this much interest. Thanks, everybody!

Can the decoder thread reach 100,000 views?

any chance you're selling a DIY kit or plans with BOM to build our own?

I have no plans for kits, as I have moved on to other projects. But I will send a zip file with all of the documentation given in the thread to anyone that desires it; just PM me with your email address.

There have been several people in the decoder thread that had bare PC boards made, and offered them for sale in the thread. I encourage anyone and everyone to do the same for the transponder.

By the way, I have enjoyed reading your threads and posts on 2.4GHz radio systems. There's a whole bunch of useful information there!

thanks for the help, tips and compliments, much appreciated!

Actually the decoder is more important, particularly if it can read MyLaps signals.

Hmm, I have a question on the drive circuitry in Howards schema. Since the output pins cannot drive the coil directly Howard uses another chip with logic gates that can source more amps. Why not simply use a transistor? Something like this:
http ://cq.cx/interface.pl#12

Above URL needs the space removed to work

You could certainly use transistor drive if you wanted. Here is why I didn't:

The XOR gates let the processor run at 1.25MHz clock speed instead of 5MHz (which exceeds the specs of the processor I originally used) and use less code space. The even harmonic output is also reduced.

When I look at the specs of the PIC12F683 processor the max clock speed seems to be 20 MHz? Should suffice by far?

If the switching artefacts is a problem, could it not be removed by a low pass filter?

Pardon my LLEK (Low Level Electronics Knowledge) :)

The 12F683 is much faster than the 12F508 processor I originally used. It had a max clock speed of 4 MHz.

Reducing low-order harmonics while maintaining the ability to follow the modulation fast enough is not easy. However, I have no proof that the arrangement I used is necessary to pass emissions requirements... But it can't hurt!

P.S. I corrected my previous post to say "even" harmonics. A square wave (as provided spproximately by the XOR gate) contains no even harmonics.

Ok, I'll guess I can experiment with it once I get my oscilloscope (need to order one). My gut feeling tells me the design could be simplified, both in HW and SW. But it is unproven. I'll post my results if and when I get them :)

On another note, if I where to build a perfboard prototype, how does the layout of the antennae design affect its effectivness? Does the diameter of the coil matter? Or is it just the turns? Need to read up on inductance...
My thinking is to build a companion board with a simple coil arrangement. That way I can build the rest of the electronics on a stripboard which would be easier to solder. So I am thinking of what is the best design for that coil design. Maybe something with a smallish ferrite in there as well?

These are all excellent ideas. I'm sure the design can be simplified, and to that end you may want to use a different brand of microprocessor.

I believe that the larger coil will give better range, since the surrounding magnetic field is also larger (but not stronger). I played briefly with a ferrite, and think that is worth further investigation.

I have used attiny85 processors for my transponder and the antenna design is 5 turns around pcb and a 1nF cap. And the numbers of turns and cap rating is very dependent to eachother and this is both calculated to be good and tested in practice to work good.

Hmm, I am so far only accustomed to the PIC processors, so I'll stick to that. But if I go higher in frequency there is more room for clever routines to send the messages with looping and branching and not just a single "thread" of execution. That would leave room for more program space and functionality I believe. Why not a button to program a specific ID number. Hold button on power up to go to program mode. Short clicks to increment number, long click to go to next number until all ID is programmed (in EEPROM). Use a blinking LED to show what is happening. Somewhat as we calibrate an ESC. To get this working we of course need to crack the ID encryption. Isn't this the solution to that:
https ://github.com/condac/openAST
I believe it is the same condac as in this thread? Right? :)

This way we could program any arbitrary ID number (within some limits of course).

Yes same person. we have found how to make a old amb id number. but it only works on old decoders, new one require a bit more. And it seems like Payalneg was on to something. If it only was to brute force what numbers that was valid or something more I don't know. But the 7 packages that have a bit counter in them that seems to go along the id number is probably what the new one also want.

I only have a old decoder so I can't test any further. My old decoder accepts numbers from 1 - 99999999 so not much verification on it..