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History  (top)

• 15sept15: lbw warmed up , worked on.
  
• aug15: a2812 reports unstable baseline. problem is polB. more info
  
• 13ju15:  change x102 freq in use. 1300 -> 1310 (punta salinas new mode a), 1175 -> 1155 (gps L5)
  
• 18sep13-> 13jun15 (file.2) x102 low band data taken in circular rather than liner polarization mode. LbwHiband was always linear.
• 09jul15:  cooling turned off because of ratcheting noise in dewar. will check after 430 run.
  
• 05jun15: lbw reinstalled in dome after vacuum window replaced. 1320 hp filters had broken shields at n-type connectors. replaced with sma cables.
  
• 11may15: problem found with lbw vacuum window.
  
• 07apr15: polB starts jumping. problem was rf cable connectors (more info)
  
• 14feb13: helium lines contaminated. warmed up, cleaned lines, cooled down.
  
• 13jan13: pointing offsets updated.
  
• 10dec12: x102 calibration on 3C138 showed that Tsys is real (not a problem with the cals).
  
• 07dec12: dewar reinstalled in dome. Dewar temps were off. they found bad power supply in postamp chassis.
  
• 04dec12: warm up dewar bring it down to lab to work on it.
  
• 27nov12: warmed up dewar, then cooled it back down. Tsys still high.
  
• 18nov12: dewar pressure relief valve blew out. warm air into dewar while still cooling. tsyspol increases, and polA now 8K > polB
  
• 31oct12: 1370 hipass filter polA was giving problems. Replaced the switches that switch this filter in and out.
  
• 12aug12: new cals installed (measured 28jun12, installed 12aug12).
• 07feb12: Tsys values and later cal measurement showed that calPolA jumped by about 20%
  
• 26oct10: lbw warmed up. knocking sound in cross head
• 28oct10: cooled back down. Knocking gone
• Tsys PolA dropped from about 32 K to 25K before/after warmup/cooldown.
• Looks like cal values changed by up to 10%. mainly polA??
  
• 25sep10: lbw reinstalled.
  
• sep10:  lbw window blown out when warming up. Brought down to lab, worked on receiver.
  
• 08may09: changed lbw cross head. Old cross head causing 1.2 hz interference in data.
  
• 26sep08: lbw cals remeasured.
  
• 05sep08: lbw warmed up looking for cause of interference. bias voltagel bulkhead cable replaced.
  
• 29aug08: lbw cals remeasured before warmup.
  
• 08jun08: lbw cryo problems.
  
• 08apr08: lbw cal box brought to lab, cables tightened. (need to remeasure cals).
  
• 02apr07: finally installed the lbw cal values that were measured back on 22apr07.
• 06feb07: tuned the bias on the 2nd/3rd stages of the dewar amp to equalize the gain in polA,polB
  
• 18dec07: found that polB had a 25% higher Tsys than polA.
  
• 22mar07: Lbw brought down to lab. Put back on telescope 03apr07. Dewar openned up and the bolts in omt were all tightened (they were loose). Trcvr was  measured on the test range. The polA resonance at 1400 Mhz (there since the jun05 dewar warmup) is not gone. The wider polB resonance around 1395 is stil present.
  
• 27oct06: upstairs iflo cable test shows loose cable in 750 mixer chassis.
• 16jun06: dewar warmed up and openned. found loose sma feed thru for polB cal. fixed. was probably causing the drifts in Tsys for polB.
• 23feb06: lbw cal value remeasured.
• 04dec05:lbw polB cal value jumps by 20%.
• 24nov05: lbw polB filter 3 (1230-1470) shows jumps in total power. This has been happening since at least last jun05 (maybe earlier).
• 23nov05: new diodes installed lbw. cal values remeasured.
• 21jul05: diode 1 lbw died. changed software to always use diode 2. This will affect polarization measurements since diode 2 introduces  a 90 deg phase shift between polA, polB outputs.
• 10jun05: remeasured the cal values after cables repaired.
• 01jun05: dewar warmed up and some cables repaired. Caused resonance in polA and polB near 1400 Mhz.
• 16may05: Tsys for lbw started jumping. (more info).
• 06aug04: cals remeasured to correct for the jump that occurred on 23apr04.
• 23apr04: Tsys polB jumped by up to 20 %. Then wandered around about for about a month. The jump was from the cal or cal cables (not the actual Tsys). see polB cal jumps
• 17feb03  New lband wide receiver installed.
• 22nov02 lband wide horn moved down 3.67" to put phase center in the correct position.
• 26aug02 lbn horn moved down 3.84" to put phase center in the correct location.

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Gain curves: (top)

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 Lband wide measurements by date:  (top)

2005

2004

2003 Images/plots of the entire band

2002

2001

2000

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Lbw measurements by topic: (top)

Specs:

• bandwidth	with only bandpass filter 1120 starts to roll off (3db down) , 1090 down by 23db 1760 start to roll off (3db down) bay 1780 18 db down

            Images/plots of the entire band

• 27sep10 300 sec integration over entire band

Resonances:

• 27nov08: trying to remove the lbw 1400 Mhz resonance in software
• 21apr07: polA resonance at 1400 Mhz gone after omt bolts tightened. PolB at 1395 still present.
• 07mar06: jun05 warmup/cooldown caused resonance in polA and polB.
• 23jun05: resonance in lbw polA at 1400 Mhz.
• 17apr03: resonances in the new lbw receiver.
• resonances in the lband wide OMT (mar02)

Cal jumps:

• 12aug12 Cal values remeasured, installed. Data shows that calPolA jumped on 07feb12.
  
• 07mar06: lbw calPolB. tapping the cables external to dewar to not change caldeflection.
• 04dec05: lbw cal value polB jumps by 20%.
• 23apr04: polB cal jumps.

Rf filterbank

• 09mar06: cycle through the 9 rf filters checking Tsys variations
• 07mar06: 1230-1470Mhz filter. See if Tsys stable when in, out.
• 26nov05: lbw polB filter 3  shows  jumps (1230-1470 Mhz)

The hybrid:

• jul01:problems using the lbw system in circular mode (hybrid in)

Compression:

• 9apr03:IFLO compression by the FAA 1350/1330 radars using lbw,lbn (29apr03).

Warmup/cooldown times for dewar:

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