[evlatests] phase jumps

[Gustaaf van Moorsel]

In earlier reports Rick has pointed out phase jumps in VLA antennas
occurring on frequency changes.  Last week I established that these
jumps do no occur when just the flukes are changed.  A further test
run last night did show the usual phase jumps when changing L6.

This observation was X-band, at four different L6 values for one
minute each.  This set of four was then repeated 14 times, for a
total of one hour.

The signature is the same: the phase jumps to a completely differ-
ent value in one scan, then jumps back to its original value in
the next scan.  The phase jumps can be of any magnitude: examples
are 35, 50, and 90 degrees.  Some antennas are worse than others
(8 and 12), others are largely free of this effect (7, 9, 10, 15,
22, 24, 25).

Gustaaf