[evlatests] Ka band status

[Ken Sowinski]

Rob was able to fix the M301/T303 communication problem yesterday
and both K and Ka bands work again.

About the only useful thing that can be done with a system that
is usable onlt at its edge frequencies is to look at the change
of focus with frequency.  That was done this morning under
reasonablt bening conditions.

The change of subreflector focus for Ka band between 26 GHz and
40 GHz is 0.15 +/- 0.02 cm; about one-sixth of the midband wavelength.
This is in reasonable agreement with, and in the same sense as,
the K and Q band measurements reported in Evla Memo 121.

Pointing is about right, but the X band pointing does not repeat well
so I don't trust it too far.  The possibilities are that it does not
track well near the zenith, or that there is some unknown pathology.
In a recent 3 dB tracking test this antenna looked "funny".  Further
investigation is needed.