Re: [Discuss-gnuradio] BBN 802.11 bbn_80211b_rx.py

[yyzhuang]

What does "combination of the LO in the front end and the digital
downconverter" mean please?


Eric Blossom wrote:
> 
> On Fri, Jul 25, 2008 at 10:11:34AM -0700, Y. Zhuang wrote:
>> http://en.wikipedia.org/wiki/List_of_WLAN_channels
>> 
>> Is it because the channel for 802.11 in 2.432G there, so the front end
>> was tuned to 2.432G? But there is 2.437G as well.
>> Or the font end is just picking the strongest channel it finds? Thanks
>> 
>> Y
> 
> None of the above.  I'm just decoding the details of how the usrp was
> tuned using a combination of the LO in the front end and the digital
> downconverter.  The command line shows -f 2.437G.  See the excellent
> USRP FAQ for additional info.  http://gnuradio.org/trac/wiki/UsrpFAQ
> 
> Eric
> 
> 
>> 
>> 2008/7/25 Eric Blossom <address@hidden>:
>> > On Fri, Jul 25, 2008 at 07:46:58AM -0400, Greg Troxel wrote:
>> >>   BTW, what does that guy mean "Not sure when you updated, but we have
>> changed
>> >>   the checked in code to default to 2437, and run it like this (as a
>> NetBSD
>> >>   rc.d start script)", following the above link?
>> >>
>> >> details if you care, but surely they have little to do with your
>> issues.
>> >>
>> >>   http://www.netbsd.org/docs/guide/en/chap-rc.html
>> >>
>> >> about your output:
>> >>
>> >>   ./bbn_80211b_rx.py -f 2.437G -v -b
>> >>   Bits Per Encoded Sample = 8
>> >>   adc frequency =  64000000
>> >>   decimation frequency =  16
>> >>   input_rate =  4000000
>> >>   gain =  45.0
>> >>   desired freq =  2437000000.0
>> >>   baseband frequency 2432000000.0
>> >>   dxc frequency -5000000.0
>> >>   Samples per data bit =  8
>> >>   >>> gr_fir_ccf: using SSE
>> >>
>> >>   2.432G is used instead of 2.437G.  Also the dxc frequency is
>> negative.  And
>> >>   no packets get printed out.
>> >>
>> >> I am unclear on dxc.
>> >
>> > That part is fine.  dxc = digital down converter (DDC) or DUC depending
>> on the context.
>> > In this case he wanted 2.437G.  The front end was tuned to 2.432G, thus
>> > the DDC needed to be set to -5M to get the desired frequency translated
>> > to 0 Hz in the complex baseband.
>> >
>> > Eric
>> >
> 
> 
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