Re: [Discuss-gnuradio] Swig error with add_item_tag

[Michael Ossmann]

On Wed, Apr 09, 2014 at 12:34:59PM -0600, Jay Radcliffe wrote:
>
> address@hidden:~/tpms-master/src$ ../src/extract_bursts.py
> ~jay/ping_903.020m_0.400m_20140403_000000z_rtlsdr.cfile
> 19.6 ********************
> T: -256, 0
> handler caught exception: Wrong number or type of arguments for overloaded
> function 'block_gateway_sptr_block__add_item_tag'.

Short answer:  It's a bug in TPMS's extract_bursts.py.  Try this diff:

- block_abs = numpy.abs(block_spectrum)
+ block_abs = numpy.abs(block_spectrum[2:-1])

Long answer:  There are two problems, and the change above is a
workaround for both.

The first problem is that the burst detection algorithm fails on your
particular capture file because the DC offset in your file is high.  So
instead of detecting six separate bursts within your file, it detects
one long burst consisting of the entire file.  The change above causes
the algorithm to completely ignore narrow signals (narrower than 3/256
of your capture bandwidth) centered at 0 Hz.

I'm going to suggest this change to Jared because DC offset is a very
common defect in SDR captures.  However, it is a trade-off.  In cases
where a capture file does not suffer from DC offset, this change could
cause the algorithm to overlook narrow, well-centered signals.

The second problem is that there is a bug that causes a negative number
to be passed as an argument that is supposed to be an unsigned integer.
I think this only happens when a burst is detected right at the start of
the input file, so the above change avoids the problem.  It's just a
workaround, not a bug fix.

Mike