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<div>Some issues arising from the K-band 24-hour observations, taken 31Jan/01Feb.</div>
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<div class="elementToProof">The power gains of most antennas changed by 25% between night and day, due to temperature changes in the vertex room. </div>
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<div class="elementToProof">PDif data corrected all these changes, to an accuracy of a couple of percent, for nearly all antennas. For a couple of antennas, the PDif values did not show this diurnal effect, as other, much larger issues caused large gain changes
occurred. In nearly all cases, PDif repaired the damage.</div>
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<div class="elementToProof">Three antennas (ea 07, 10, and 12) had warm dewers — Tsys values of 400 K were reported. The data from these antennas are of little use for imaging, but still gave good gain curves deteminations, as the sources we use for this are
all very strong. </div>
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<div class="elementToProof">New gain curves were derived for all antennas except ea01 (no PDif) and ea17 (out of the array). The usual antennas with large elevation dependencies measured in the past (notably ea15 and ea18) still have them. </div>
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<div class="elementToProof">Cross-polarization values were 'decent' for all antennas — in the 5 to 10% range. There is a notable periodicity in the 'D' terms amplitudes for all antennas, of period 250 MHz — corresponding to a reflection separation of ~60 cm
(free-space equivalent). </div>
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<div class="elementToProof">One troubling effect was noted: The R-L phase difference varied by tens of degrees for many antennas. This is a significant concern for accurate polarimetry. (The lower frequency bands that I've reviewed all showed similar effects,
but of much smaller amplitude — a few degrees at most). These differences at K-band, for some antennas, showed a temporal dependence that looks like they are temperature induced, but for other antennas, and for all antennas later in the run, there was no
obvious time function. The large phase differences, and the variations between antennas, make it difficult to impossible to choose a good 'reference' antenna (defined as one which has no R-L phase difference changes over time or pointing position). The effect
of calibration is to induce into the measurements of the linear polarization position angle an error equal to the reference antennas phase difference (divided by a factor of 2). Having a varying changes of tens of degrees in the reference antenna will play
havoc with accurate polarimetry. </div>
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