[evlatests] K-Band Efficiencies

[Rick Perley]

    We have measured the K-band efficiency on antenna 14 through
observations of Venus, at three frequencies, 18440, 23560, and 26120 MHz.
    The details will be in an EVLA Memo, to be released by next week. 
   
    Summary:

    We used a 5 x 5 raster at 4 points/beam, with off-source baseline
calibration to remove the system power offset.  A focus adjustment was
made based on tracking Venus -- the error was about 5 mm for each
of the three frequences (hence, there is little movement of the optimum
focus as a function of frequency).  [Note:  Ken Sowinski has measured
the focus error interferometrically, but does not see so large an 
error.  His
observations were made at 60 degrees elevation, while ours were at
27 degrees -- perhaps the difference is the known change of focus with
elevation].
    Using 54.0, 81.9, and 97.4 Jy as the (unattenuated) flux density of
Venus, and adjusting by the known opacity corrections at each
frequency, we find:

    59% at 18440 MHz
    53% at 23560 MHz
    50% at 26120 MHz

    Minor corrections from pointing and subreflector positioning could
make small (~1%?) increases in these values. 

    The flux densities used are last week's values, increased by last
week's secular increase (2.1%/day), as provided by Bryan.  He will
provide more accurate values later today.  If there is any significant
change, I'll send around amended values.