430 dome PolB gain is low. jul-oct12

• source B0618+145 (3C158)
  
• 7.45 Jy at 430 MHz. size~7"
• .2% polarized at 1405 (via nvss)
• 16 patterns done. 
• Each pattern consits of 4 strips each +/- 3 beamwidths
• az strip,za strip, +45 deg strip, -45 deg strip. There are 60 samples/strip.
• Each pattern has a 10 second cal on ,cal off.
  
• freq/bw: 430/25MHz, 430/12.5MHz, 429/1.MHz,431/1MHz
• the 430MHz 25 and 12.5 MHz bandwidth have some rfi.

• The cal deflection  for each pattern was used to scale the data to Kelvins.
• You can see the source deflection for the 4 strips.
  
• Each frame is a different freq/bandwidth dataset
• the 16 patterns have been over plotted.
• polA is black, polB is red.
• The tsys for the two polarizations is within a few kelvin
• The source deflection varies by a factor of 10.
  
• the  jumps in the 1st two frames are rfi
• The rfi jumps in polB are much smaller than the rfi jumps in polA
• 430gr is circularly polarized so this difference is probably not a polarization problem.
• looks like there is not much signal getting in from the sky

• Page 1: 14oct12 x102 data.
• I processed  stokesI (a+b), polA, and polB separately.
• Top: gain vs za in K/Jy
• stokesI = 6K/Jy. This is 1 about 1/2 of the expected value
• polA= 11 K/Jy. this is the expected value
• polB= 2 K/Jy. This is much less that 5x less than expected.
• 2nd frame: tsys vs za
• PolA is around 70K while polB is about 65K. This difference could be explained by inaccuracies in the cal values.
• 3rd frame: SEFD = Tsys/Gain
• this is independent of the cal values (since both gain and Tsys use the cal value)
• polA is around 6 Jy (expected) while polB is 30Jy. stokes I gain is around 10Jy.
  
• if the gain of one pol went to 0, the sefd for stokes I would get 2 time bigger.
• Bottom frame: average beam width
• The average beam width is 650 asecs. this is the expected value.
  
• The beam widths for stokesI, polA, polB are all the same
• This says that the optics and telescope gain are probably ok.
• Page 2-4 show the 430 dome x102 data for jul-oct12
• page 2: StokesI gain,tsys,sefd, and average beam width
• The data agrees with the stokes I data from 14oct12.
• page 3: stokesI pointing error
• The top 2 frames are za Error vs za,az, the bottom 2 frames are az error vs za,az
• there is a 17 asec za offset and 8 asec az offset. the rms  are 10.8 and 7.5 asecs
  
• page 4  gain,Tsys,sefd, and SEFDPOLb/SEFDpOLA for stokesI, polA, and polB
  
• the 3 freq bands are shown with different colors
• + is polA, * is polB
• Gain. i've used a log axis for y. polA is around 10K/Jy, polB is around 1K/Jy
• tsys: The tsys for polA and polB are about the same
• SEFD: polA is around 6Jy while pol B is 20 to 100Jy
• sefdB/sefdA the ratio is 10 to about 60.

When did it start?

• x102 430data was taken on:
  
• low Gain  (5-6 K/Jy) on 15may12,01jul12,14aug12, 07sep12,14oct12.
• normal gain (11 K/Jy) on 24oct09
  
• There was no 430 x102 data between these two dates
• A2599 on/off position switching on continuum sources mar/apr2012 (.ps) (.pdf)
  
• This show source strength in degK vs freq.
  
• Black is polA, red is polB
• PolA and polB have close to the same value for the source in degK (using the cals).
• The values were ok on 02apr12.
• x111 430dome  rfi mar-jul 2012 (.ps) (.pdf)
• The x111 (rfi monitoring data) for mar-jul12 was used to see any gain differences
• The processing was:
• each 60 second scan was averaged.
• the average spectra was converted to deg K using the cals
• The Peak rfi for polA and polB was located in each spectra
• The plots show the Peak rfi in polA and polB with the other pols value over plotted.
• The peaks for polA and polB did not have to be at the same channel.
  
• Black in polA, red is PolB. The dotted green line is the end of each month: mar,apr,may,june.
  
• Top: PolA max Value with corresponding polB value from this channel.
  
• Bottom: polB max value with corresponding polA value from this channel.
• There are measurements where polA is larger than polB, but it is not consistant.
  

Summary:  (top)

• The gain in polB is about 10% of the expected gain.
• The gain in polA is correct
• the system temperature for polA and polB are about the same value 65-70K.. this is the expected value
• This means that any problems are occurring before the cal injection.
• If there is a 90% gain loss after the cal injection then the Tsys from the dewar would go up by a factor or 10. This would probably be noticeable.
  
• RFI coming into polB is much weaker than the rfi coming into polA (and 430gr is circularly polarized).
• The SEFD also shows a factor of 10 difference between the two pols
• the sefd does not use the cal values, so it is not a cal value problem.
• The beam widths are identical for polA, polB  and stokesI.
• this means the telescope gain is ok
• The pointing error has
  

• 	offset err asecs		rms err asecs
  	az	za	az	za
  polA	.6	19.0	5.8	9.9
  polB	46.9	19.8	10.4	10.4

  
  
• So the beam squint is about 45 asecs. This is what it has historically been. This is not enough (with an 11 amin beam) to cause the large drop in source deflection.
  
• The problem must be before the cal injection and it is not the optics. There is either a bad cable (capacitively coupled?) or the omt is not working for polB
• if the omt is bad, it has to be bad only for polB leaving polA functioning correctly?
• How long has the problem been present.
• The problem is in the x102 measurements since 15may12 - 14oct12
• The problem was not seen in the 24oct 09 data. there is no x102 data between 24oct09 and 15may12
• a2599 took data on 02apr12 and the problem was not present.
• Looking a the strength of rfi in polA,B does not give a consistent measure of the gain (probably because the rfi is coming in through a far out sidelobe and is not being passed equally between the two pols.