[evlatests] S and C band RFI

[rperley at nrao.edu]

Bob Hayward and I did some tests a year ago on the prototype S-band
system, using the 'Bandpass Tool', which provides good frequency
resolution over a 1 GHz-wide bandpass.  I have reviewed these plots taken
with a center frequency of 3800 MHz, (hence showing the spectrum from 3300
to 4300 MHz).  The results are interesting ...

The data taken with the antenna vertical, and pointing at Cyg A (high
elevation) appear fine.  But the 'tip' data, taken mostly at low
elevation, show moderate level RFI, extending more or less uniformly
between 3600 and 4200 MHz.

Last year, at the SKA 'ImCal' meeting held here, Gary Harp (from ATA)
showed similar spectra, similarly messed up from what he said were
satellite downlinks.  It would be useful to get a better understanding of
what these are (if indeed this is the correct explanation).

We have much to learn about the environment we are trying to work in ...