Convert HackRF Mayhem Portapack capture to a format playable with hackrf_transfer

I had a nice capture of a busy 40m band done using a HackRF Mayhem portapack and I wanted to play it back using a HackRF connected to a computer using hackrf_transfer.

Even though the native format of the hackrf IQ is 8 bit signed interleaved samples, for some reason the portapack pads these out to 16bit so conversion is needed.

A utility to do this is here.

Here's how it looks being played back:

These captures are excellent for demonstrating receivers and playing with decoders for digital modes. Note that the files can get rather large.

I play the output file back like this: hackrf_transfer -t 40mssb.iq8 -f 7100000 -x 1 -R