[evlatests] summary; 4 band; antenna 26

[Ken Sowinski]

X band:  all antennas appear to work
C band:  13, 14 and 16 work
          14C seems low, but the problem is not delays or
          signals levels up to the VLA T5 module.
K band:  13, 14, 16 and 18 work
          13 still has erroneously low SD voltage.  Ateenuator
          levels for BD need adjusting if we know we are not
          going to remove the pads at the Rx output that installed
          last week.
L band:  13, 14, 16 and 18 work
Q band:  13, 14, 16 and 18 work
          ea16-l302-1 did not lock.
          14C (again!) is low, but the problem is not delays
          or signal levels up to the T5 module.
P band:  14 and 18 work, sort of.
          18 seems to have dipole or hybrid problems:
           AA  CC  AC  CA
          .15 .40 .25 .08  (about the same for BD)
4 band:  14 and 18 work, again, sort of.
          14 looks OK; 18 has a very strong birdie in AC.


4 band
May have failed when Mark tried it because the default setup
frequecies were incorrect; these are now corrected.  When I
got things setup correctly there was plausible data from 14
and 18BD; 18AC did not look as good.  An examination of spectra
revealed a very large birdie in the A and C IFs.  LOs were tuned
to achieve a DC edge of 73.01875 MHz.  The birdie was seen
about 300 kHz above the band edge in IF A, and about 400 kHz 
higher in IF C.  Nothing other than the usual interference was
seen in 14.

There are two ways to setup EVLA antennas for 4 band.  What I
did was to choose P band and request the band edge to be 73.01875 MHz
rather than the usual P band frequency.  This works, but uses the
P band table values for setting attenuators and the subreflector.
The preferred way is to ask for 4 band; I haven't tried this yet,
but it is now more likely to work since the default setup frequencies
have been corrected.


Antenna 26
Antenna 26 was not available this morning, but I report on work
done on Tuesday; that was the first time the antenna was available
since it was first shown to work.  I was able to set focus and
delays for IFs A and C, but the response is still down by about
a factor of ten in power.  This afternoon I will try to look at
pointing.  If that does not fix it we have something broken in
the signal path or LO.