[evlatests] Ku-Band report from flux densities run
Rick Perley
rperley at nrao.edu
Wed Mar 5 17:21:42 EST 2025
A short summary of issues seen in the Ku-band data, from the 24-hour run taken 31Jan/01Feb. (apologies for late report, but there's a lot to sort through ...)
27 antennas in the array — ea17 was out.
3 antennas (ea07, 08, 12) had warm cryos (!!!) — Tsys about 250K. Data are useable, but very noisy.
One antenna (ea01) had non-functioning switched power.
Major gain changes were seen in all antennas, from various causes. In almost all cases, application of switched power reduced the gain changes from tens of percent (or larger) to about 1 percent.
1.
The 30 C change in the ambient temperature caused a 25% (!) change in correlated visibilities, with a time function clearly connected to the outside temperature.
2.
a few antennas showed occasional big gain changes, (> 10%) with no obvious cause.
As noted, application of switched power corrected all of these, except:
1.
ea01 — which had no switched power
2.
ea21 — the switched power looked great, but the calculated gains showed amplitude (and phase) changes on timescales of a few seconds. Gain fluctuations are in the 10% level. Cause unknown.
New elevation gain curves were derived for all antennas except ea01 and ea17. The results for ea21 are less secure, due to the rapid gain changes noted above.
Cross-polarization ('D' terms) were very low (~ 2 — 4%) for most antennas. (Note —since I'm using 8-bit samplers, I see only 1 GHz-wide chunks centered at 14 and 16.5 GHz). Exceptions (all in the upper frequency window) are: ea03 (6%), ea21 (10% above 16.5 GHz), and ea24 (20% above 16.7 GHz).
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