PolA Tsys high
09sep15: calibration run shows that problem is not
the cal values.
28sep15: TsysLoad, antenna show that large
Tsys Difference only occurs on antenna
The 430 ch receiver signal path is:
- turnstile to
- jennings relay (load,sky coax switch)
- polA -> monoplexor
- polA,B -> receiver.
The monoplexor should add about 20 K to the
Historically we've seen the temperature difference between
polA and polB range from 20 to 50 Kelvins .
The plots show:
Particular dates are:
- Top Frame: tsys polA (black), polB (red) for the year
- bottom frame: TsysPolA - tsyspolB for the year
tsys 430ch (.ps) (.pdf)
- for most of 2014 TsysPolA-PolB was 10 to 20 Kelvins
- may14-jun14 it had jumped up to a difference of 40 K
- on 28Dec14 Tsys jumped to a difference of about 45 K.
tsys 430ch (.ps) (.pdf)
- For most of 2015 tsysPolA-polB was about 45K.
- 28dec14: last 430tsys with polA-B diff <=20K
- 28dec14:from operators log:
Ast Time: 22:20
Project : INFO
Comments: There was a loud sound behind the rack 6. as the sound of a
short circuit. The experiment could not continue because of
this. I checked the rack and the chassis 6-19 30 MHz - 260
, Converter box had no power. Checked the rack 6 breakers
and had tripped. I reset it and resolved the problem.
- After this delt Tsys was about 40K
- 15jan15: coax switch polA (jennings relay) replaced
09Sep15 - calibration run with ch
On 9sep15 x102 calibration runs were
done with the ch 430 system.
The plots show the sep15 calibration
run results (.ps) (.pdf)
These plots show that the tsys difference is a
true temperature difference and not a problem with the cal values.
- Top: gain (K/Jy) vs za. Black is polA, red is polB
- 2nd: Tsys vs za
- 3rd: SystemEquivalentFluxDensity (SEFD) vs za
- sefd is Tsys/gain. It is independent of errors in the cal
- Tsys and gain both use the cal value. Their ratio cancels
the cal value.
- bottom: Ratios polB/polA
- Black SEFDA/SEFDB, green: TsysB/TsysA
- You can see that the tsys ratio is the same as the sefd
ratio (which is independent of the cal value)
28sep15: Tsys on load and sky.
Tsys was done on sky and then load around
11:15 on 28sep15... the measured values were:
When we were on load, the polA,B difference was
only 20K. When we were on sky, the difference was 50K.
The monoplexor is after the load/sky switch. If it was the
problem, we should have had a large temperature difference whether
we were on load or antenna. These results point at the
problem being the jennings relay load/antenna switch.
- TsysPolA - TsysPolb for the ch 430 has been about 45 Kelvins
- Comparing the ratio of sefdA,B to the ratio of
TsysA,B shows that the Tsys difference is independent of
the cal value (so the problem is not a problem with the cal
- Tsys on load,antenna from 28sep15 showed that the large pola,B
difference only occurs on antenna. On load, the difference is
- This shows that the problem is not the monoplexor (since it
is present on load and antenna).
- The problem is probably the jennings relay.