[evlatests] X-Band status, Modcomp-free, 26 June

[Jim Jackson]

I just checked while the system was in X-band (about 3:45PM MDT).

I see nothing in the hardware to explain why Antennas 19 & 21 did not work.

Antennas 13 and 14 have been having EDFA problems. These have just 
been swapped to spare EDFA's. I wouldn't trust anything before about 
3:30PM MDT today.  We also had extra problems bringing 13D up and 
some monitor points in the D351-d are not behaving - there does 
appear to be good RMS, TP and SD values. We believe the IF-D signal 
should be good but won't know for sure until we power cycle and check 
the module tomorrow.

Antenna 18 IF-A is dead due to a bad D351 deformatter - it will 
likely be changed tomorrow, Thursday at the latest.  We don't 
currently have spares - Kerry just completed final assembly on a few 
more and is testing them overnight.

The drops on 26AC sound like synthesizer lock issues we see 
occasionally - we are looking into those in the L302 design and calibration.

Antenna 16 will need some more looking into.

Jim


At 03:18 PM 6/26/2007, Rick Perley wrote:
>     After appropriate flagging was (manually) done on the observations
>referred to in the prior note, I find:
>
>     1) Antennas 14, 19, and 21 are dead at all IFs.  It is noteworthy
>that none of these were flagged by the system.
>
>     2) Antenna 13A and 13B are very weak.  Antenna 13D is dead.   The
>amplitudes of all three 'working' channels are not behaving normally,
>with oscillations and 'clunks' occurring on many timescales.
>
>     3) Antenna 16C has three different levels, at 0.0, -1.6, and -3.8 dB
>in power.  There is a fairly clear periodicity in the pattern of drops
>-- 1.2 second period.   The 'zero' level defined above is itself below
>what would be considered normal, by about -3 dB.
>
>     4) Antenna 18A is fixed at a high (erroneous) level, with exactly
>180 degrees of phase on all baselines.
>
>     5) Antenna 16B has extremely unstable gains, varying by ~50% or
>more.    These are clearly related to large claimed changes in Tsys,
>seen in the tables.
>
>     6) Antenna 26 has three small 'short shallow drops' on IFs A and C
>only.
>
>     Overall, phases look pretty good, other than steady winds likely
>related to large baseline errors.  There are a multiplicity of small
>clunks and slopes, which I have come to understand are due to the VLA's
>phase and delay compensation system.  All of these are of 5 degree
>amplitude or less.
>     Some VLA antennas have steady phase winds.  For this observation,
>nearly all of these are on the west arm (6, 8, 4, 5, and 22).  The rate
>increases more or less with baseline length.  It is curious to me that
>this is not seen on the east arm, except for antenna 15.  In particular,
>antennas 3 and 20 (at E64 and E48, respectively) have nice steady
>phases.  It is possible we hit the stationary point (which happens once
>per day) by accident in this observation, but what's the probability ?
>Either that, or a fortuitous atmospheric wedge positioned itself just
>right ...  Similarly, all north arm phases are flat, except for minor
>slopes for antennas 7 and 26 (which are of opposite sign).
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