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Re: [Discuss-gnuradio] USRP2 Sample 2.4 GHz Channel

From: Miklos Christine
Subject: Re: [Discuss-gnuradio] USRP2 Sample 2.4 GHz Channel
Date: Wed, 16 Sep 2009 17:08:04 -0700

Yes, that is exactly what I'm looking for. However, when running usrp2_rx_cfile.py with decimation = 4, I get a 'S' printing to stdout. Is anyone else able to run usrp2_rx_cfile.py and not get that overrun message?
What could be the reason for 'S'? Is it a limitation on how fast we can write the samples to the hard disk?
I want to keep the maximum number of samples possible.

Miklos Christine

On Wed, Sep 16, 2009 at 6:52 AM, Douglas Geiger <address@hidden> wrote:
When you say sample the channel - are you trying to look at the I&Q
samples coming right out of the USRP2? In which case, the easiest way
to start would be to use the usrp2_rx_cfile.py script, then you can
load the file into Matlab/Octave/etc. to take a look at. If you want
to record samples coming out of one of a block in the flowgraph (e.g.
in the 802.11b scripts) - you can modify the flowgraph to connect up a
file_sink at each point you want to record data from.

On Tue, Sep 15, 2009 at 9:41 PM, Miklos Christine
<address@hidden> wrote:
> Hello,
> I'm trying to sample the 802.11b wireless channels but the USRP2. I'm
> currently using revision 10689 of Gnuradio.
> I've added code to bbn_80211b_rx.py to connect the gr_probe_signal_f() to
> the top block.
> To sample the channel, I use gr.probe_signal_f().
> Here's the code to connect the block:
> self.connect(self.u, self.conv_c2f, self.probe2)
> Then I use the gr.probe_signal_f().level() to retrieve the signal in a loop.
>     data_file = open('data.txt', 'w')
>     T1 = time.asctime()
>     while cs_samples < 1000000:
>         CST = self.tb.probe_channel()
>         data_file.write(str(CST) + '\n')
>         cs_samples += 1
>         data_file.close()
>     T2 = time.asctime()
>   def probe_channel(self):
>     """
>     """
>     return self.probe2.level()
> I was wondering if this is the fastest way to sample the channel from
> python. When I compute how long this process takes, it appears that I can
> get a sample every 8-9 microseconds, which seems a lot slower than what the
> USRP2 is built to do. Am I sampling the channel in an incorrect way?
> I'm running this on a machine with a Intel Quad Q9650 @ 3GHz.
> Thanks,
> Miklos Christine
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

Doug Geiger

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