Hi All, in all the examples and in my own gnuradio Programm, there is an unknown Peak in the FFT-Plot sink. Here is the Screenshot: http://img257.imageshack.us/img257/8017/nochstrender.jpg How to avoid this ? Wherefrom does this come ? I attach my Program to this mail, but i think it is still ok. I need this to measure the power of the noise. Further on you see the noise has a wave form always in the middle of the FFT-Plot, still when i watch another spectrum. In the gnuraio example from Eric B. this doesn't appear, but this example only use a sin-signal-source not a usrp-source. How to avoid this ? I tried to change the decimation and the sample Rate, but doesn't solved this. Regards Markus

on 2009-03-20 14:07

on 2009-03-20 18:36

Use an Intermediate Frequency (IF) and frequency translating filter. Paul M.

on 2009-03-21 15:38

Paul M. <opto <at> whidbey.com> writes: > > Use an Intermediate Frequency (IF) and frequency translating filter. > Paul M. I still use the IF by tune my usrp source with, usrp.tune(self.usrp_source, 0, self.selected_device, self.usrp_freq) But i think you mean to tune the "frequency translating filter" ?! Therefor i want to know what is <tabs> ? I read <channel filter>. Is this equivalent to <bandpass filter> or do you mean the IO-Ports from the DA-converters ? Sorry but i didn't learned the english translated technical term. How to fit up this <frequency translation filter> ? # USRP SOURCE self.usrp_simple_source_x = grc_usrp.simple_source_c(which=0, side='B', rx_ant='RXB') self.usrp_simple_source_x.set_decim_rate(decim) self.usrp_simple_source_x.set_frequency(freq, verbose=True) self.usrp_simple_source_x.set_gain(gain_usrp_source) # FREQU. TRANS. FILTER self.gr_freq_xlating_fir_filter_xxx_0 = gr.freq_xlating_fir_filter_ccc(decim, (1, ), freq, samp_rate) # FFT PLOT SINK self.wxgui_fftsink2 = fftsink2.fft_sink_c( self.GetWin(), baseband_freq=0, y_per_div=10, y_divs=8, ref_level=80, sample_rate=samp_rate, fft_size=512*2, fft_rate=20, average=True, avg_alpha=None, title="FFT Plot", peak_hold=False, ) When i start this, it seems to be busy ! When i tune the freq with my slider, all 3 elemts will be tuned. Is this correct? Or should i set up the baseband frequency of the fft plot to 0Hz ? Any Hints ? Regards Marksu