Sbh tsys polB high: dec19
dec19
The sbh receiver warmed up on 04nov19. It was
cooled back down on 26nov19. During this period there were changes
in the measured Tsys.
- 03nov19: before warmup:tsysA: 28K , tsysB: 28k
- 26nov19: after cooldown: tsysA: 60K , tsysB: 35k
- 02dec19:
tsysA: 27K , tsysB: 35K
After the cooldown both TsysA and TsysB came
back higher, then on 02dec19 polA jumped back down to its
pre-warmup value.
The plots show sbh Tsys PolA,
and PolB as well as TsysPolA-TsysPolB for 2019 (.ps) (.pdf)
- Top: Tsys polA, polB.
- The warmup at the beginning of nov, and then TsysPolB
remaining higher in Dec.
- bottom: TsysPolA - TsysPolB
- The large difference occurred on 02dec19.
SEFD shows real tsys problem.
A change in Tsys could be a problem with the cals
used to measure the Tsys, or a real problem with the system
temperature.
The SEFD is the ratio of Tsys/gain. Since both of
these measurements use the cal values, the ratio cancels out the cal
usage. If the SEFD shows a change, it is not because of a problem
with the cals values.
On 07dec19 and x102 run tracked 3C48 with the sbh
receiver.
The plots show the SEFD changing
similar to the Tsys change (.ps) (.pdf)
- Page 1: measured Tsys and SEFD
- The colors show different frequencies: black: 3300,
red:3500, green: 3628, blue: 3800 MHz
- + lines are polA
- * lines are polB
- Top: Tsys:
- The polB values are about 8K higher than polA
- bottom: SEFD:
- PolB SEFD is higher than the polA SEFD.
- Page 2: PolA/PolB ratios
- top: TsysA/TsysB
- The average value of the ratio is plotted next to each
frequency.
- Bottom: SEFDA/SEFDB
- The average values of the sefd ratios are similar to the
Tsys Ratios.
SUMMARY:
- After the warmup, cooldown cycle of sbh starting on 04nov19)
polB Tsys was about 25% higher that polA
- SEFD measurements done on 07dec19 also showed the polB SEFD
about 17% higher than polA
- This shows that the polB tsys change is not a problem with the
cal value.
- The high polB Tsys is a real problem with the system
temperature. Probably a problem in the dewar.
processing: x101/191222/sbhpol.pro
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