[USRP-users] decimation rate for gsm-receiver-usrp.py

Red Gator redgatormds at gmail.com
Sat Sep 20 13:19:54 EDT 2014


Never mind.

The gsm_receive_usrp.py example looked "old" for B210 UHD, so I took the
gsm_receive_rtl.py example, stripped out the osmosdr source and stuck in
the UHD source based upon the UHD_FFT generated Python code.

Hacked code runs like a champ! Ref:
http://www.rtl-sdr.com/rtl-sdr-tutorial-analyzing-gsm-with-airprobe-and-wireshark/

$ diff -btw gsm_receive_rtl.py gsm_receive_b210.py
16a23
> from gnuradio import uhd
49a57,74
>   def _set_source(self, options):
>       # from uhd_fft.py example
>       address=""
>       self.uhd_usrp_source_0 = uhd.usrp_source(
>           ",".join((address, "")),
>           uhd.stream_args(
>               cpu_format="fc32",
>               channels=range(1),
>               ),
>           )
>       self.uhd_usrp_source_0.set_subdev_spec("A:A", 0)
>       self.uhd_usrp_source_0.set_samp_rate(int(options.sample_rate))
>       self.uhd_usrp_source_0.set_center_freq(options.frequency, 0)
>       self.uhd_usrp_source_0.set_gain(options.gain, 0)
>       self.uhd_usrp_source_0.set_antenna("RX2", 0)
>       self.uhd_usrp_source_0.set_bandwidth(options.sample_rate, 0)
>       return self.uhd_usrp_source_0
>
65c90
<     self.src = osmosdr.source(options.args)
---
>     self.src = self._set_source(options)
67,75c92
<     self.src.set_sample_rate(int(options.sample_rate))
<
<     if self.rfgain is None:
<         self.src.set_gain_mode(1)
<         self.iagc = 1
<         self.rfgain = 0
<     else:
<         self.iagc = 0
<         self.src.set_gain_mode(0)
---
>     # self.src.set_sample_rate(int(options.sample_rate))
76a94
>     self.iagc = 0
79c97,98
<     sample_rate = self.src.get_sample_rate()
---
>     # sample_rate = self.src.get_sample_rate()
>     sample_rate = self.src.get_samp_rate()


On Fri, Sep 19, 2014 at 4:37 PM, Red Gator <redgatormds at gmail.com> wrote:

> There is an interesting application called airprobe that allows an SDR to
> decode GSM signals.
>
> I have it mostly working with a B210, but it's acting like the decimation
> rate is wrong, and I am frankly clueless with regard to how to determine
> the appropriate deci rate.
>
> The RTL-SDR uses a decimation of 64, and the USRP1 uses 112.
>
> Can somebody suggest a decimation rate for the B210?
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20140920/f2e22ebc/attachment-0002.html>


More information about the USRP-users mailing list