spike center of band:sbc1 polB jul-aug11
A 1 channel wide spike was found in the center of sbc 1,
polB using the interim correlator. It did not occur with the 25 Mhz
The plots show an example of
the problem (.ps) (.pdf):
- spike in center of the band, 1 channel wide.
- Only found in polB
- Found in bandwidths 12.5,6.25.. all the way to 195 Khz
- It was not found in the 50 or 25 Mhz bands
- It was seen in 3 level (and stokes) and 9 level configurations.
- It existed:
- 27jul11 13:00 first appeared
- 12aug11 13:00 problem went away.
- We started to work on the problem
- cycled power on halfband filter chassis (problem remained)
- removed halfband filter chassis from rack, opened the
chassis and started running the program so we could probe things
- Projects affected by this:
- a2600: 30jul11,31jul11
- a2619: 28jul11,31jul11
- a2585: 30jul11,31jul11
- a2598: 30jul11, 31jul11
- page 1: spectra (5 sec average)
- black 3 level, red 9 level
- frame 1,2: 25 Mhz polA,polB
- frame 3: 12.5 Mhz polA
- frame 4: 12.5 Mhz polB
- the spike is 1 channel wide at the center of the band
- The spike was seen in all bandwidths below 25Mhz (but no in 25
- Page 2: total power tsys versus bandwidth (3 level)
- + symbols polA
- * symbols polB
- the sbc's are colored
- red: sbc2
- The large spike is causing the Tsys to increase.
- Page 3: total power tsys vs bandwdith or 9 level
- A large spike in the center of the band (5 times Tsys) occurred
- polB sbc1 bandwidths 12.5Mhz and below, 3 and 9 level
- it was present 27jul11 13:00 thru 12aug11 13:00
- It took so long to find the problem because there was a two
week 430 Mhz world day run starting at the beginning of aug11.
- The problem disappeared after we opened the halfband filter
chassis and reran the program
- cycling the power did not make the problem go away
- when opening the chassis we had to disconnect and reconnect the
cables to the halfband filter chassis.
- The operators reported a power dip 27jul11 in the morning.. they
may or may not have had something to do with it.
- The initial band starts out as 50 Mhz with the a/d dc spike on
the left of the band.
- As the bandwidths are halved, the a/d dc spike is removed.
- A spike in the center of the band has been seen before (sep 2002)
but at a much weaker level.
- For each bandwidth, the clock for the next narrower bandwidth
lies in the center of the band. eg:
- for 12.5 Mhz bw, the 6.25 Mhz clock is in the center of the
12.5 Mhz bw
- This does not explain why the 25 Mhz bandwidth did not have a
spike.. so maybe something else was wrong.
up_to_interim cor page