new amps installed Aug14

Intro

    The sbn Chalmers amplifiers were damaged Aug13 during an sband run. The sband hi amplifiers were installed in sbn while the sbn amps were being repaired.
We received the repaired Chalmers amps and began installing them jul/aug14.

• The polB (labeled inside the dewar) amp  was installed 15jul14. 
• This replaced the old sband hi amplifier
• the cables from the amps to outside the dewar are swapped, so the new amp will be PolA on the outside world.
  

Timeline:

• jul14: new Chalmers amp installed (polB in dewar, polA outside dewar)
• 31jul14: calibration run. single pattern on each of 3 sources
• 06aug14: polB rf cable (dewar to if/lo blue cabinet) found to have a bad outer shield. repaired.
• 19aug14: calibration runs on two source done

The plots show the results of the runs (.ps) (.pdf)

• B0017+154, B0138+136, B2353+154 were done prior to repairing the polB  rf cable
• B1843+098, B2120+168 were measured after the polB  rf cable was repaired
  
• Page 1: stokes I gain,tsys,sefd,beamwidth
• The SEFD for B1843+098 is a little high
• This could be a problem in the flux, or
• Tsys was probably a little higher since this source is close to the galactic plane
  
• Page 2: polA,polB separate, gain,Tsys,sefd
• + is polA, * is polB
• The gain for polA is higher than expected. It is 20% higher than polB
• these sources are not circularly  polarized, so the gains should be equal
  
• The sefd for the new amp is about 10% better than polB
• B1843+098 is the exception. It's sefd for A,B *,+ are about the same.
• Not sure how galactic polarized power could make a difference in 2 circulars?
  
• The cals were not remeasured (for that matter they weren't remeasured when the sbh amps were installed).
• the cal value for polA is probably too large. This makes the gain and Tsys  too large.
• 
  

Summary:

• The cal value for polA is probably about 10-20%  too high
• the new Chalmers amp works better than the old Chalmers amp
• Fixing the rf cable between the dewar and the blue cabinet did not change the Tsys.
• The source B1843+098 does not show a difference in polA,polB sefd..
• the only difference i can think of is that this source is close to the plane of th galaxy.