Re: [Discuss-gnuradio] Output of usrp_rx_cfile and Input of ATSC demodulator

[Brian Padalino]

On Nov 29, 2007 5:13 PM, Dan Halperin <address@hidden> wrote:
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> Wuest Brandon-WTVR47 wrote:
> > I am having a problems with disk writing not being able to keep up with
> > the high data rate, so I am trying to do a little manipulation of the IQ
> > data to get around this.  What I am trying to do it get 8-bit samples
> > from the usrp (which my disk can keep up with) and then before I feed
> > that in to interp.py, I convert every pair of bytes to a complex<float>.
>
> A logical approach if your disk can't handle 32MBps linear write.
>
> I'll answer question #0 first:
>
> For converting pairs of bytes to complex, this might seem a bit (really,
> a lot) silly, but a simple way to do it in GNU Radio would be
>
> gr.file_source(gr.sizeof_char,"file") ->
> gr.char_to_float() ->
> gr.float_to_short() ->
> gr.interleaved_short_to_complex()
>
> You could also write a gr.interleaved_char_to_complex() block (which
> appears to not exist in gnuradio-core/src/lib/general) which would be a
> MUCH better solution but would require effort :-D.

So I had this idea just sitting here after coming home from work and I
pose it as a question - why do the stored complex samples have to be
stored as complex?

Because they are orthogonal to each other, shouldn't there be a simple
way to generate real samples (possibly at some simple intermediate
frequency instead of at baseband) and automatically half the number of
samples that need to be written?  Could you use a simple scheme of
{+1, 0, -1, 0} for your IF for mixing and still retain most of the
information?

Has anyone tried something like this to reduce the amount of data
required for sustained writes?  What do people think of the
feasibility of such a system?

Brian