Re: [Discuss-gnuradio] GMSK receiver question, USRP tuning?

[George Nychis]

The decimation should not affect the amplitude of the waves, right? 
Which if you look at the graph, the GMSK receiver has ~4x the amplitude.

I agree that the decimation has affected what looks like the frequency, 
but otherwise it should look the same and not affect my ability to 
decode it.  Something else seems different between test_usrp_standard_rx 
and the GMSK receiver.

- George


Dan Halperin wrote:
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> The default decim in the C++ program (which, IIRC, is deprecated) is 8.
> What decim (what bitrate?) are you using for GMSK?
>
> - From the graphs, it looks like data from the C++ app is coming in about
> 4x too fast.
>
> - -Dan
>
> George Nychis wrote:
> > Hi all,
> >
> > I'm using benchmark_tx.py to transmit a GMSK sequence at 10MHz.  As some
> > of you know, I'm trying to debug my own GMSK m-block receiver.
> >
> > If I use test_usrp_standard_rx -F 10000000 (not the in-band receiver) to
> > capture the incoming signal and plot it, I get the graph on the top, and
> > if I dump the data coming out of the usrp1_source_c block when running
> > benchmark_rx.py -f 10000000, i get the bottom graph:
> > http://www.andrew.cmu.edu/user/gnychis/std_gmsk.png
> >
> > I can successfully decode the transmission with my receiver using the
> > data output from usrp1_source_c and benchmark_rx.py ... however I cannot
> > decode it using the samples from test_usrp_standard_rx.
> >
> > So I'm wondering, what is benchmark_rx.py tuning on the USRP differently
> > than test_usrp_standard_rx?  Of course, my goal is to duplicate this
> > action because my in-band code is also dumping data similar to the top
> > graph.
> >
> > Thanks!
> > George
> >
> >
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>
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