Projects a2703 reported baseline problems
with lbw polB on 07apr15 . I looked at the following data:
- a2703 07apr15. they used lbw
- a2940 07apr15 they used the mocks
The first plot shows the total power
vs time for a2703 data (.ps)
- band 1 was 12.5 MHz, band2,3 were each 25MHz Bandwidth
- the frequencies were around 1380 MHz.
- Black is pol A, red is polB
- the vertical scale is units of Tsys (i divided by the
- You can see polB jumping by up to +/- 2% Tsys
The 2nd plots shows the total power vs
time for the a2940 data on 07apr15 (.ps)
- This used the wapps. Black is polA, red is PolB.
- The negative going spikes are compression caused by the
- I used the rms/channel for each scan to remove frequency
channels with rfi prior to computing the total power.
- For the first 400 seconds, polB was jumping around by up
to 2% of Tsys.
On 08apr15 we used the interim correlator to monitor the lbw
total power while the techs wiggled the lband wide rf cables
- lband wide, cfr 1410 MHz, linear pol.
- We sent the same signal into all 4 boards of the interim
correlator. 25MHz bandwidth, 1 second integrations.
- When polB started jumping around, we used the crossover
switch to switch the polA,B cables before the first
- When we did this, the problem switched to polA. This
showed that the problem was before the first mixer.
- We then had the tech's wiggle the rf cables before the
first mixer while we took data.
The plots show the total power
vs time during the wiggle test (.ps)
- Black is polB,red is polB
- Pol B was misbehaving until around second 1300 (green
- At the green line, we tightened the connector on the polB
cable that exited the dewar
- this stopped the jumping
- the tech said the cable wasn't loose
- At the blue line we started moving the polB cable that
went from the lbwfilterbank output to the blue cabinets
- this caused polB to jump around again
- the tech tightened this cable (but he said it wasn't
- After that we wiggle all of the polB and polA rf cables,
banged on the dewar, but saw no more jumps
- PolB rf cable exiting the dewar was causing problems.
- The connector was tightened and things stopped jumping
(but the tech said the connector was not loose)
- PolB rf cable exiting the lbw filter bank caused jumping
in the total power when it was wiggled.
- The connector was tightened and the problem stopped (but
the tech said the connector was not loose)
- Seems like some of our cables are overly sensitive to
being moved.. even when tight..