[hpsdr] Wide bandscope

[Tom McDermott]

Hi Bob -

The number of samples was increased from 4096 to 16384 a few years ago in
Protocol 1 FPGA code.
I don't know the effective FPGA revision number, but it was probably 2013
or so.

The data rate would be very high if sent continuously, so 16k samples are
time-contiguous but then
there is a large time gap until another 16k contiguous time set, etc.  I
treat each block as a 16k vector
of time samples.

These are 16-bit raw samples, 2's complement fixed point, real (not
complex), and have not been decimated.
So the noise floor is not lowered by decimator integration.   If you do an
16k FFT on the vector you will
get a two-sided result.

If there is a bandpass filter in front of the ADC then the spectra will be
shaped.   In practice most
receive antennas / tuners will also shape the spectra.  A very broadband
antenna and no filtering
would be needed to achieve relatively flat spectra.

I implemented a wideband gnuradio module for this, you can look at the C++
code at
https://github.com/Tom-McDermott/gr-hpsdr/blob/master/lib/hermesWB_impl.cc
I don't know if that will help as much of the processing is gnuradio
specific.

-- Tom, N5EG
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