polB if1 attenuator failing

• sbn shutter closed (to give a stable power level)
• 750 mixer used ( we also looked at the 750nb mixer with similar  results).
• a set of  tcl commands in /home/online/Tcl/Proc/test/attnloop.pro were used to cycle through the attenuator settings:
• set attenuator
• measure power if upstairs power meter
• step the attenuator values and repeat.
• we went
• 0 - 11 in 1db steps
• 0-11 in 2db steps
• 0-11 in 3db steps
• 0-11 in 4db steps
• 0-11 in 5db steps
• ...
• 0-11 in 11 db steps.
• We then repeated this.
• We ended up with 98 measurements (each with polA, and polB).

The plots show the power levels for the various attenuator settings (.ps) (.pdf):

• The horizontal scale is the attenuation used
• the vertical scale is the measured power (in db).
• I removed a constant value so that polA and polB had similar power levels.
• black is the polA reading, red is the polB reading.
• The blue labels at the bottom show which internal attenuators were used for each setting.
• each attenuator internally has 1,2,4, and 4 db attenuators.
• for 8db attenuation and above, the 2nd 4db attenuator for polB never got inserted (when requested).
• there were two instances (out   of many) where the 2db attenuator did not get inserted for both polA and polB (at 2 and 10db)

Summary:

• we need to replace the if1 attenuator  for polB.
• The two failures in the 2db atten for both a and b  may have been attenuators,, or it could have been a communications problem. We can probably leave the polA attenuator  in.
• These hp attenuators have the ability to verify that the attenuation switch worked correctly.
  
• This capability was disabled in  oct15 because we were living with a bad  attenuator.. it might  be a good idea to re install this checking (after the new attenuator get installed).