spike center of band:sbc1 polB jul-aug11

• 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
• problem went away.
• 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 Mhz)
• Page 2: total power tsys versus bandwidth (3 level)
• + symbols polA
• * symbols polB
• the sbc's are colored
• black:sbc1
• red: sbc2
• green:sbc3
• blue:sbc4
• The large spike is causing the Tsys to increase.
  
• Page 3: total power tsys vs bandwdith or 9 level

Summary:

• A large spike in the center of the band (5 times Tsys) occurred for:
• 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.