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<p>Did the T304s reset attenuators between runs? I'm sure they did
when you went to a calibrator. So much interference in P-band, I
wouldn't be shocked to see significantly different attenuator
settings from run to run.<br>
</p>
<p><br>
</p>
<p>Rob</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 10/28/2024 1:58 PM, Rick Perley via
evlatests wrote:<br>
</div>
<blockquote type="cite" cite="mid:DM4PR14MB713223D2BCE7255E746234CBD74A2@DM4PR14MB7132.namprd14.prod.outlook.com">
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<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
I ran a holography test last night (to assist Tracy Clarke in
her characterizations of the P-band primary beam). The SB
consisted of four single cuts through the primary beam. The
four cuts were: horizontal, vertical, and two cuts at 45 degree
angles. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Each holography cut begins and ends with a short on-source
calibrator observation. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
A most remarkable thing happened between the first two
holography cuts in last night's test:</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
The amplitude changed, for all antennas. Some amplitudes went
up, others went down. For some antennas, the change was barely
noticeable. For others, it was as large as a factor of six.
(!). The changes were not the same in the two polarizations. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
The effect is due to a gain chang, and not to any antenna or
subreflector position error —it is seen in the switched power
monitors —both PSum and PDif. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
The PSum values, at the beginning of the run, and through to the
end of the first holography observation, were normal at near 14
counts. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
This gain change occurred only after the first holography scan —
about ten to fifteen minutes into the observation. For all
other beam cuts, the gain remained constant (at the wrong power
levels). </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
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Any idea what happened? </div>
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<br>
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Rick</div>
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