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I can explain what happened with the changing gains. <br>
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The 'digital' gain values were forgotten after the first holography scan. <br>
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In more detail:</div>
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The first scan in the SB was a slew to source, at C-band. </div>
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The second scan was a 1-minute observation of the calibrator, to set the analog gain. New gains were implemented very quickly — within about 10 seconds. <br>
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The third scan was a 10-second observation of the calibrator, to set the digital gain. This resulted in PSum values close to 15 for all antennas, all SPWs. As they should be. </div>
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The next two scans were separate observations of the calibrator, followed by the four observations within the holography script: calibrator, holography setup, holography scan, calibrator. </div>
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It was at this point that the Psum values all reverted back to exactly the same levels they were after the second (analog gain setup) scan. </div>
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So it is clear that the system 'forgot' the digital gain setting. </div>
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Rick</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> evlatests <evlatests-bounces@listmgr.nrao.edu> on behalf of Rick Perley via evlatests <evlatests@listmgr.nrao.edu><br>
<b>Sent:</b> Monday, October 28, 2024 2:12 PM<br>
<b>To:</b> Rob Long <rlong@nrao.edu>; evlatests <evlatests@nrao.edu><br>
<b>Subject:</b> Re: [evlatests] A remarkable gain change at P-band</font>
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All setups were done according to instructions: After moving to the source at a different band, a 1-minute on-source observation, at P-band, was executed for the T304 gains, followed by a 10-second observation to setup the digital gain. These worked as expected
(so far as I can tell). </div>
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Rick<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Rob Long <rlong@nrao.edu><br>
<b>Sent:</b> Monday, October 28, 2024 2:08 PM<br>
<b>To:</b> Rick Perley <rperley@nrao.edu>; evlatests <evlatests@nrao.edu><br>
<b>Subject:</b> Re: [evlatests] A remarkable gain change at P-band</font>
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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>
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<p>Rob</p>
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<div class="x_x_moz-cite-prefix">On 10/28/2024 1:58 PM, Rick Perley via evlatests wrote:<br>
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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>
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Each holography cut begins and ends with a short on-source calibrator observation. </div>
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A most remarkable thing happened between the first two holography cuts in last night's test:</div>
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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>
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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>
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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>
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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>
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Any idea what happened? </div>
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Rick</div>
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<pre class="x_x_moz-quote-pre">_______________________________________________
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