[evlatests] pdiff and noise tubes

[Ken Sowinski]

I examined P_diff for all antennas over all bands with the noise
tubes turned off, to be sure that noise tubes were controllable
for all receivers and to see if any antennas had especially large
P_diff while the nopise tubes were off.

The K band noise tube at ea14 could not be turned off; all others
behaved as expected.

For most bands the peak-to-peak variation in P_diff, over
antennas and time was around .005, consistent with the expected
noise in 128 MHz taking the difference of two half second
integrations.  The exceptions were L band at about 0.1
(interference?), C band and X band which were about .04

A more careful survey is needed, especially at C and X bands.
Datasets called ?nttest, where '?' is a single letter band code
were taken between 1700 and 1730 UT this morning.  Each consisted
of a few minutes with the noise tubes alternating on and off every
20 seoncds.  The antennas were all stowed during these tests.