OOK demodulator (10 MHz in, 12kbps UART out) ;

[Warhawk]

Hello Everyone,
I am reverse-engineering communication between my old Futaba 12Z model hobby transmitter and the 2.4 GHz RF module. That thing is quite over-engineered for today's standards. It was designed back in 27/35/40/72 MHz times and when the 2.4 GHz came they had to find a way how to make it compatible with their high-end model. For this reason, there is UART-like communication between the base unit and the 2.4 GHz module using OOK modulation (fmod=10 MHz). This was originally used to modulate the old MHz band modules. The 2.4 GHz module has an RF demodulator, MCU, and RF ASIC which explains the price back then . I guess that was the only way how to do it back then.

Now comes my question. How would you implement the demodulator?

At the moment I do it discretely as shown in the attached picture. A simple AC-coupled amplifier boosts the signal and an envelope detector does demodulation. Then I feed the signal to a comparator in the MCU which inverts the signal and does level-translation for the UART periphery. It works in general but I somehow feel It could have been better. I was also looking at MAX9930 or LTC5507. What do you think about it? How would you do it if you needed something like this for a commercial product?

I guess you're curious why I am doing this: I'd like to use FrSky protocol using TI's CC2500 and learn something new.

Thanks for any thoughts.

Jiri :]