I am trying to transmit a 1 KHz sine wave using a USRP2 with carrier 2.48 GHz. I use,
usrp_siggen.py –f 2.468G –x 1k --sine -A 0.5 -v Verbose gives:- Interface: eth0 MAC Address: 00:50:c2:85:33:fa D-Board ID: 0x2b USRP interpolation rate: 16 USRP IF bandwidth: 6.25MHz Set TX gain to: 0.0 Set center frequency to 2.48GHz Tx baseband frequency: 2.49375GHz Tx DDC frequency: -13.75MHz Tx residual frequency: -4.65584mHz Set baseband modulation to: Complex Sinusoid Modulation frequency: 1kHz Initial phase: 0 TX amplitude: 0.5 Then with a second USRP2 using a different host I try to receive 1M complex samples at a centre frequency on 2.48GHz and write them to a .dat file. I use, sudo ./usrp2_rx_cfile.py -e eth1 -d 16 -f 2.48G -g 35 -N 1000000 -v out.dat Network interface: eth1 USRP2 address: 00:50:c2:85:33:f7 Using RX d'board id 0x0027 Rx gain: 35.0 Rx baseband frequency: 2.48125G Rx DDC frequency: 1.25M Rx residual frequency: 4.65679m Rx decimation rate: 16 Rx sample rate: 6.25M Receving 1M samples Writing 32-bit complex floats Output filename: out.dat Finally I try to read the binary .dat file created and plot the signal over time and the FFT. I use, sudo ./gr_plot_fft.py -B 1000000 -R 6250000 out.dat In the FFT with a block size of 1M the peak is not at 1KHz (verified using matlab) and in time I also receive high frequency signals. I basically get some sort of AM modulation and a fixed message frequency shift. Can anybody tell me why these effects are present. Transmitting signals in the MHz range the frequency offset is around 190KHz independant of the actual message frequency (1MHz, 2MHz....etc....). Best regards, Marc. http://old.nabble.com/file/p27701654/rx.jpeg -- View this message in context: http://old.nabble.com/Data-aquisition-and-plotting-FFT-tp27701654p27701654.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
