[Difx-users] vex2difx bandwidth-sample rate check

[Joe Skeens]

Hello all,

I've been working with a couple of collaborators on running DiFX with
complex signals, and we've found something that looks like it may be an
oversight. In the vex2difx file 'vexload.cpp,' there's a simple if
statement check which seems to ensure the sample rate is above the Nyquist
frequency:

if(bandwidth - stream.sampRate/2 > 1e-6)

This causes vex2difx to exit on an error condition for bandwidth greater
than sample rate divided by 2, but for a complex signal, the signal is
only undersampled for bandwidth greater than sample rate. Commenting out
this check and rebuilding DiFX seems to correct the problem. Is there
something I'm missing with respect to how the bandwidth is processed in
the channel definitions under $FREQ in the .vex file, or has this check
been designed with only real signals in mind? Thanks in advance for any
insights.

Best,
Joe Skeens
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