Example data set generated during the 2017A GBT observer training workshop.
This particular file has two data extensions because for the first part of 
the session VEGAS was configured to use 32768 channels, and during the second 
half it was configured to use 4096 channels.
It is the use of different numbers of channels that triggered the creation of
two data tables within the SDFITS file, not the change between frequency 
switching and total power.