Sbh tsys polB high: 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
tsysA: 27K , tsysB: 35K
After the cooldown both TsysA and TsysB came
back higher, then on 02dec19 polA jumped back down to its
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
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
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
- Bottom: SEFDA/SEFDB
- The average values of the sefd ratios are similar to the
- 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
- The high polB Tsys is a real problem with the system
temperature. Probably a problem in the dewar.