[Discuss-gnuradio] Problem with USRP PSK modulation

[Vivian Paola Triana Galeano]

I think my problem has something to do with the parameters of the USRP. 

I  try to send a file modulated with BPSK. So I build a graph like this :

File source -> Packet Encoder -> PBSK MOD -> PBSK DEMOD -> Packet Decoder -> File sink

and i really get the correct output file with thee right constellation.
 
If I put a USRP source and USRP sink into graph, I don't receive anything.
I hope anyone can help me. Thanks