Re: [Discuss-gnuradio] saturation with multi_fft.py

[ematlis]

Thanks-

I just downloaded, compiled and installed this latest revision.  When I 
test multi_scope.py in the mutli-antenna examples directory with this 
release I get the same issue.  Please note, I have the LF_RX 
daughterboards, so I change the daughterboard ID from BASIC to LF in the 
python code.  I also eliminate the second factor of 4 decimation in the 
host (sw_decim = 4) by setting it to 1.  I then run with the following 
command:

multi-antenna]$ ./multi_scope.py -f0 -d250 -g0

while acquiring a 10 kHz 0.3 V p-p signal.  The max value shown in the 
waveform on the gui is just over 25,000, which is way too much compared to 
the standard usrp_fft.py, which by the way is no longer in the examples 
directory; I used one from a previous release.  If I increase the input 
voltage level to 0.4 V p-p, I get a jagged waveform with sharp 
discontinuities.

So, my problem remains.  Any ideas?

thanks,
eric

On Tue, 9 Oct 2007, Eric Blossom wrote:

> On Tue, Oct 09, 2007 at 03:02:33PM -0400, address@hidden wrote:
> > Thanks so much for clarifying that!  I see now that config.vh controls how
> > the code is configured.
>
>
> FYI, I've committed new rbfs to the trunk.  They were built with
> Quartus II Web Edition, version 7.1 SP1
>
>
> > Regarding the loss of the half-band filters in the multi-antenna fpga
> > configuration; what is the recommendation to avoid aliasing?  Say for the
> > case of a 2 MHz carrier AM waveform with modulation out to 100 kHz.  What
> > kind of filtering would I need to avoid aliasing?
> >
> > thanks again,
> > eric
>
> With the halfbands, it's flat to about 70% of the passband.
> decim = 320 gives 200kS/s complex baseband, a bit more than you'll
> need.
>
>
> Without the halfbands, I'd use about 4x the bandwidth of interest,
> then filter and decimate in the host for the final channel selection.
> In your case, I'd use decim = 160 giving 400kS/s.
>
> Eric