[Discuss-gnuradio] FSK with TX-RX in ISM-band 433 Mhz

[Luis Simoes]

Hi all,

I am a novice in gnuradio and after searching in a lot of forums I put my USRP 
working and my Gnuradio running. Some FM and AM reception with and without 
GUI are working fine. Now I have some problems in FSK. I try to receive in 
ISM 433 MHZ some data packets with a data rate of 38.4 kbaud. The data is 
manchester encoded. To do this I followed the way in the gnuradio examples 
(fsk_rx.py) with a channel filter and the simple correlator. To do the 
correct manchester decoding I changed the correlator block in according to my 
needs and build the new block howto_manchester_correlator. The difference 
between my manchester_correlator and the simple correlator is the packit 
function and the sync bytes (instead of using GRSF_SYNC I use MAN_SYNC= 
0x66669999, these are the preamble and syncronization bits).
Now when I start my application gnuradio starts receiving some data that is 
written to a file, but my transmitting module is switched off and the data is 
complete nonsense. When I switch on the transmitter the result is the same. 
This occurs also when I ran the application with the simple correlator. The 
seqno where in random order, but there should be nothing because I didn't 
send anything in the simple_framer format. Now I think the correlators are 
working well but the problem can be on the radio part.
My system is working on Linux-kernel 2.6 (Linux 9.3) and the CPU is AMD Athlon 
XP 2400+
I have tried to adjust all parameters with no result.

I am very grateful for any kind of help or advice.

Luis