polB if1 attenuator failing
The upstairs if/lo has two sets of
attenuators: rf attens (before the mixer) and if1 attens
(after the mixer). These attenuators to 0 to 11 db in 1 db
steps. When testing the sbn receiver on 11dec16, we saw that
the attenuator values for polB if1 attens were jumping around.
Normally the if1 attenuators are not needed ..
Sbn started needing the if1 attens when the 2355-2360 rfi got very
On 12dec16 we ran a test to see if the if1
attenuators were working ok.
The setup was;
- sbn shutter closed (to give a stable power level)
- 750 mixer used ( we also looked at the 750nb mixer with
- 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
- 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
processing : x101/161212/tstif1attn.pro
- 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