Sbc4 polA highTsys
Tsys is taken daily with the interim correlator. The
same signal is sent to all 4 interim correlator board (sbc's). On
18Aug12 (after an aeronomy run) tsys polA from sbc4 was higher than
the values from polA sbc1-3. This continued will 27Aug12. The
problem properties were:
On 20Aug12 some
tests were done to see where the problem was occurring (.ps) (.pdf):
- The temperature was stable over many days.
- The amount of temperature difference depended on the bandwidth
the interim correlator was using.
We then switched the outputs of the half band filter for 3a,4a. When
we did this, the problem moved to sbc3A
- The setup
- cband at 5Ghz was used
- the same signal was sent to sbc1,2,3,4
- 25 MHz bw, calon, caloff
- when switching the input cables, the power levels were set
- The off cal was scaled to kelvins using the cal
- The spectra from each sbc was ploted using a different
- Frame 1,2: polA
- frame 1 signal goes straight through. 4A has higher Tsys
- frame 2: switch inputs 3a,4a to the digitisers. sbc 4A
- this implies that the problem is after the digitizer
- Frame 3,4 polB
- frame 3: pol B signal goes straight through
- frame 4: pol B signal goes straight through.
On 27Aug12 we
- This shows that the problem is in the half band filter
- Cycling the power on the half band filter chassis did not fix
After the problem went away, I took some data measuring tsys for bandwidths 25MHz ->.19MHz
for 9 and 3 level sampled (.ps) (.pdf):
- removed the half band filter chassis from the rack
- opened it up, looked at it, and then closed the chassis
- reinstalled the chassis in the rack
- After this the problem went away.
Some similar icorr problems:
- Page 1: Tsys 9 level bandwidths 25 MHz to 195 Khz.
- Each board is plotted in a different color
- The bandwidth numbers are 50MHz/(2^}(n-1) ,, n=2..9
- + is polA, * is polB
- Page 2: over plot the polA spectra
- Page 3: Tsys 3 level samlpling.. bandwdidths=25,....
- Page 4: over plot the 3 level spectra.
- 9 level polB sbc1 has a Tsys that is about .4 K larger than
the other values ??
- 22jun11 Tsys function of bandwidth. Problem was half band
filter power supply
- 15Aug11: spike in center sbc1 polB. problem went away when we
removed and the re installed the chassis.
- 18jun12: tsys sbc4A tsys increased. The increase was a
function of the cor bandwidth used.
- The problem was in the half band filter chassis.
- A higher tsys could result if the half band filter was
configured incorrectly and a wider bandwidth was pushed
through when a narrowing was expected.
- 27Aug12: removing the chassis, replacing the chassis made the
problem go away.
- Cycling the power did not make the problem go away.
- on 15Aug11 we had a spike in the center of the band. It went
away when the chassis was removed, re installed.
- switching the rf input cables did not change the
- One of the control cables to the half and filter might be
making lousy contact. Removing and reinstalling the chassis
could reseat it.
- The datataking code used is under usr/x101/src/src.27Aug12.
up_to_interim cor page