[evlatests] EVLA Characteristics from last evening

[Jim Ulvestad]

Did you use the Modcomps?

I thought you used to say that G was worse, but compensated
by lower Tsys.  Now it appears that Tsys is worse too?
It would be unfortunate to not meet spec. at L band.

ju

>     From last night's long blank-field integration at L-band:
>
>     All 10 EVLA antennas up and running.  However:
>
>     1) 21C gave all zero visibilities.
>     2) 18 B and D gave only noise.
>     3) 19B was only barely alive -- very poor sensitivity.
>     4) 19D was only slightly better than 19B.
>     5) 14B and D are still doing the 40 degree bi-stable phase bit that
> I described yesterday.
>     6) 24A and C have some data drops.
>
>     In addition, amongst the VLA antennas:
>
>     1) 28D gave spectral with oscillating amplitude -- a sawtooth
> pattern.  A correlator problem which I understand is being corrected.
>     2) Antenna 4, all IFs, shows brief data drops.  This problem has
> been going on for a couple weeks, at least.
>
>     Otherwise, data quality was very good.
>
>     Sensitivity:
>
>     I calculated the antenna-based sensitivity, via ANBPL.  In general,
> the EVLA antennas are all significantly poorer than the VLA antennas, as
> has been reported many times.  These observations were taken at very
> high elevation (above 70 degrees) where the discrepancy between EVLA and
> VLA is maximized.
>     Antenna 24 is the only one whose sensitivity is comparable to the
> average VLA antenna.  All others are from 15 to 30% lower in G/Tsys than
> the median VLA.
>     The worst EVLA antennas (in sensitivity at L-band) are:  21, 17, 13,
> and 14.    In general, it seems that the problem lies with Tsys.  For
> all four antennas, the reported (back-end) Tsys values are 40 to 80 K.
> We can correct for errors in Tcal by noting the change in Tsys when
> going onto the calibrator -- presuming the antenna efficiencies are
> about 50%, we should get about 1.5K extra.  The values observed are
> close, although in some cases, a downward correction is suggested.
>
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