Re: [Discuss-gnuradio] Matlab signal detection/analysis

[Eric Blossom]

On Tue, Jun 24, 2008 at 11:36:34PM +0200, Jake Hertenstein wrote:
> Hello all,
> 
> I am attempting to analyze data sets recorded by the USRP in Matlab for
> the purpose of signal detection/analysis. The signal detection
> requirement must be met by identifying prominent signals and returning
> the frequency and signal strength. In doing this I have come to identify
> several important questions which I cannot answer myself:
> Given a known decimation, how can one determine the sampling rate of an
> output data file?
> Since the "tuned" frequency is subtracted from the signal, how can one
> apply the FFT in Matlab to identify the original signal's frequency?
> What are the units of the data file values?
> 
> Thanks in advance,
> Jake

You don't say, but I'm assuming that the data is being recorded
using usrp_rx_cfile.py.  The files contain nothing but the binary
samples.   You may want to consider encoding the decimation rate and
center frequency in the filename, or writing the file using something
other than gr.file_sink(...).  Note that in general, the guts of GNU
Radio have no clue as the actual sample rate of data streaming through
the blocks.  That's a feature, not a bug.

If the decimation is D, the complex baseband sample rate is 64e6 / D.

Eric