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Regarding the variation seen in L-band Tcals before 2019, that was
the period we were doing solar cal upgrades to L, S, C, X, and Ku
band receivers. On L-band specifically, all 30 receivers were
upgraded with solar cal capability, which involved adding an
amplifier and adjustable attenuators into the existing cal injection
path. The Tcal levels were re-characterized after each upgrade.<br>
<br>
The final receiver of 102 modified (L-011) was done on 6/13/2019,
completing a 6 year-long campaign. That coincidentally lines up with
what you observed in the data.<br>
<br>
-Wes<br>
<br>
<div class="moz-cite-prefix">On 9/3/2026 1:57 PM, Rick Perley via
evlatests wrote:<br>
</div>
<blockquote type="cite" cite="mid:DM4PR14MB7132F228FA981C46FF908E82D7B62@DM4PR14MB7132.namprd14.prod.outlook.com">
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The procedure to generate 'sky-calibrated' Tcals for our noise
diodes allows investigation of long-term stability. </div>
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The results for Ku-band are especially illuminating. </div>
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As described earlier, we use the known flux density of 3C286 to
generate corrected values for the noise diode temperature. </div>
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For Ku-band, there are 14 antennas whose receivers have not
changed since 2019. I show below the derived values of Tcal at
13.936 GHz. </div>
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Ant Rcvr# 2019Jan31 2019Oct24 2021Sep09 2023Oct03
2025Jan31 2025Mar09</div>
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RCP LCP RCP LCP RCP
LCP RCP LCP RCP LCP RCP LCP</div>
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01 16 1.56 1.85 1.65 1.86 1.52 1.74
1.53 1.73 - - 1.51 1.80</div>
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03 13 0.70 0.78 0.69 0.81 0.68 0.75
0.69 0.80 0.67 0.79 0.69 0.79</div>
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04 17 1.93 1.88 1.99 1.94 1.89 1.84
2.00 1.87 2.00 1.88 2.00 1.85</div>
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05 14 2.23 2.35 2.32 2.41 —- ---
2.37 2.48 2.42 2.44 -- --</div>
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07 05 1.79 1.82 1.78 1.78 1.86 1.81
-- -- 1.41 1.25 1.86 1.82</div>
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09 19 1.79 1.77 — -- 1.69 1.73
1.70 1.76 1.81 1.82 1.71 1.74</div>
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11 27 1.30 1.26 1.30 1.30 1.31 1.45
1.33 1.41 1.34 1.39 1.34 1.44</div>
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15 28 1.24 1.30 1.27 1.36 1.40 1.46
1.45 1.57 1.38 1.47 1.33 1.41</div>
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18 12 1.89 1.87 1.99 2.00 2.25 2.29
2.34 2.39 2.32 2.34 2.28 2.31</div>
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19 02 1.90 1.90 3.58 3.18 1.50 1.42
1.58 1.50 1.52 1.47 1.56 1.47 Values in 2019
questionable</div>
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22 07 3.00 2.99 2.91 3.04 3.06 2.82
3.20 2.97 3.19 2.98 2.99 2.89</div>
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23 24 1.70 1.71 1.68 1.74 1.70 1.68
1.74 1.67 1.75 1.67 1.73 1.66</div>
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26 25 1.24 1.15 1.19 1.20 1.17 1.17
1.20 1.16 1.25 1.16 1.19 1.18</div>
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28 06 —- --- 1.47 1.35 1.51 1.43
1.55 1.43 1.51 1.44 1.51 1.45</div>
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Except for ea19 (whose very different values in 2019 have no
ready explanation), the rms stability over time, for a given
antenna/receiver/polarization is between 2 and 4%. Curiously,
for the four antennas with the same receivers prior to 2019
(dating back to 2014) show Tcals about 10% lower than the
numbers shown above. Other bands, particularly L-band, show
considerable variations in their derived Tcals for dates before
2019. After this date, all bands that I've investigated so far
(L through Ku) show similarly to the numbers above, for nearly
all antennas. </div>
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The few percent variation from year to year for a given antenna
is easily accounted for by temperature variations of the
switched diode, pointing variations, and sky opacity differing
from the simple model used in the gain calibration. </div>
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