[Discuss-gnuradio] Re: FSK4 Demodulation on the FPGA

[ikjtel]

> Hey all,
> Has anyone attempted to implement a C4FM demodulator on the Altera
> Cyclone in the USRP1? Right now I'm hoping to do this to read 
> P25 encrypted packets on the FPGA instead of on the CPU, and I 
> wanted to know if it was possible. If so, could anyone could 
> point me to any sort of examples or tutorials I could learn
> from to accomplish this? It would be greatly appreciated.

Kevin

We've got this working - although at present the code runs in the PC as a GNU 
Radio application.

Assuming you want a receiver implementation that's entirely USRP based, you 
would also need some other blocks in addition to the C4FM demod block -
 - channel selection, downconversion to zero IF
 - decimation
 - FM demod
 - post-demod filtering (i.e., RRC filter)

No idea if there is sufficient gate array capacity in the FPGA to implement all 
this, or not.

Anyway, here are a few links to get you started 
 - http://sites.google.com/site/radiorausch/
 - http://sedition.org.au/op25/
 - op25-dev yahoogroup
The RadioRausch pages do not load properly for me.  Nonetheless, you want to go 
to the "four level FSK" page.

You would be most welcome to join the op25-dev group also.

Best of luck

Max