[evlatests] Temperature-sensitive gains at Ku, K, Ka, and Q bands

[Jim Jackson]

I just looked - the temperature inside one UX converter cycled over 
only about 5C over a 24 hr period.  I'll have to talk to the guys 
tomorrow about whether that could explain anything like this - I'm 
skeptical that it could.

Jim


At 02:04 PM 10/31/2011, Rick Perley wrote:
>     The elevation-gain test taken early Saturday morning strongly
>supports Michiel's evidence for temperature-sensitive gains -- and at
>all the high frequency bands (Ku, K, Ka, and Q).
>
>     A strong change in PDif was noted in the tests taken the preceding
>week -- of a source setting from 82 degrees elevation to elevation 8.
>All high frequency PDif values *increased*, by typically 10%, during
>this period.  It was difficult to be sure that the visibilities changed
>by a similar amount, since the test was of a single source setting
>during the period.
>
>     The data taken Saturday morning were of a source which was rising at
>midnight, and transited at dawn.  Temperature effects were minimized,
>while the elevation vs time was reversed (i.e., the source was rising,
>rather than setting).  The PDif values for this run rise during the run
>-- but by a much smaller amount than the previous week's test.
>
>     We can rule out an elevation dependency of the PDif.  And we can
>strongly favor a temperature-dependent gain, since the vertex room
>temperatures should considerably lag the external air temperature.  Both
>of my runs were taken when the air temperature was declining (the first
>one strongly so, the second one only slightly), while Michiel's test --
>which showed the opposite variation in PDif -- was taken with strong
>heating.
>
>     Application of the PDif values gives an elevation-dependence of the
>gains which appears to be the same for both of my runs -- this
>strengthens an explanation that the PDif changes are due to real gain
>variations, and not due to a changing value of the noise diode power.
>
>     Rick
>
>-------- Original Message --------
>Subject:        [evlatests] Q-band holography d.d. 2011-10-29
>Date:   Mon, 31 Oct 2011 12:37:02 -0600
>From:   Michiel Brentjens <mbrentje at nrao.edu>
>To:     EVLA Tests <evlatests at nrao.edu>
>
>
>
>** [2011-10-31 Mon 12:11] Q-band holography d.d. 2011-10-29
>
>Temperature sensitive gains?
>----------------------------
>
>A 3C273 Q-band holography observation from past Saturday shows a
>systematic decrease of PDIF over the course of six hours in virtually
>all antennas. This *decrease* in accompanied by a similar slow,
>systematic *decrease* in visibility amplitude. Typically, PDIF
>decreases by 20%. The visibility amplitudes also show a 20% decrease,
>although they are much noisier than the PDIFs.
>
>The source had a fairly constant elevation between 36 and 57
>degrees. The observation began at 08:00 MDT and ended at 14:00
>MDT. Are we seeing a temperature dependent Q-band gain here? Notable
>exception is IF 3C, which shows nicely constant PDIFs, yet also
>decreases its amplitudes along with all others.
>
>
>Other phenomena
>---------------
>
>For some reason, 11R lost all signal around 16:50 UTC. After 17:30
>UTC, the PDIFs of 20L become increasingly more noisy, until they
>suddenly snap together at a higher value around 19:05 UTC. 12A PDIFs
>are consistent with noise. 4L PDIFs behave nicely until 17:00, at
>which point they increase by 50% and begin behaving erratically.
>
>- Michiel
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