Intro

    A new sbn receiver was installed in the dome on 28oct12. It has:

• A new dewar.
• The omt is now cooled
• A new horn
• The horn illumination was  changed.the  illumination of the tertiary was increased. This should increase the gain (and maybe tsys a little)
  
• The sbtx horn was also replaced.
• the tertiary illumination was increased to give a slightly better gain (tsys isn't important for the xmit horn).
• On 26nov12 the new sbn receiver was moved in the z direction by 1.2 inches to move it into  focus.
  

14nov12: rcvr Tsys contributions:

    The old sbn receiver had:

• lna with 40db gain
• postamp1 chassis with circulator, filter,3db pad, 30db amp.
  

    At installation the new sbn receiver had:

• lna  with 30db
• postamp1 chassis with circulator, filter,3db pad, 30db amp
• postamp2 chassis with 36 db gain.
  

• lna  with 30db
• postamp1 chassis with circulator, filter,3db pad, 30db amp
• 10db pad
  
• postamp2 chassis with 36 db gain.
• 15db (polA)  20db (polB) pads
  

• There are two runs:
• first with the current configuration (14nov12)
• 2nd add a 14db amp and 3db pad before the filter
• The final Tsys is  off since the sky and lna temps may be low.
  
• Current config (14nov12) largest Tsys contributions are:
• .2K from filter
• .65 K from 3db pad
• Tsys: 15.4
• Final gain going to iflo cabinet: +64db
  
• Config with 14db amp:
• 14db amp gets rid of the above tsys contributions
• Tsys 14.4
• The 14db amp improves Tsys by about 1K
• Final gain
• with 2nd postamp: 75db
• removing 2nd postamp and 10 and 15 db pads: 64.5db
• This is the same gain as the current (14nov12) setup. It will probably be "better" because the extra 11 db gain (14-3) is before the filter. This should put the sky 10db higher above the noise floor without saturating the downstream components (since the filter limits it to 120 MHz). The if/lo may want a few more db gain to be happy.
  

23nov12:Compare old/new rcvr (out of focus) Calibration runs:

    Calibration runs done during oct12 with the old sbn rcvr are compared to calibration runs done with the new receiver (on 23nov12). The new receiver was 1.2 inches out of focus during these runs.
     There were  2 common sources:

• B0518+165 (3C138). A standard calibrator with about 9% polarized power (linear).
• B0758+143 (3C190)

• Page 1: gain,Tsys,SEFD, beam width
• These use stokes I (which is the sum of polA + polB).
  
• Page 2: coma, 1st side lobe height, main beam efficiency, main beam + 1st side lobe efficiency.
  
• Page3:  Pointing error. za,az error vs za, then za,az error vs az (in arcsecond).

• StokesI:Old receiver performance (oct12 all sources) (.ps) (.pdf)
• StokesI:New receiver performance (23nov12 all sources) (.ps) (.pdf)
• gain,sefd
• Looks like the flux for B1040+123 is too high by about 15%.
  
• Pointing:
• there is a 7Asec offset in za and az.
• 
  
• StokesI:Old, new receiver with common sources over plotted (.ps) (.pdf)
• The new receiver source names end in _New (black,green). The old Receiver source names end in _Old (red,blue)
• Gain.
• The gain drops from za=10 down to za=2.
  
• This is probably because the elevation rails are shimmed incorrectly
• The gain for the new receiver drops a little faster than the old receiver.
• This may be because the receiver is out of focus be about 1 inch in the Z direction.
• Tsys:dropped from 25,5  to 23K.
• Since this measures stokes I, it includes polA and polB.
  
• the old receiver had TsysA=24, tsysB=30K.
• the new receiver has TsysA,B both equal to about 23K
• so the stokes I improvement is mainly from polB.
• SEFD:
• old: : 2.7 Jy
  
• new: 2.3 Jy
• This is probably from the polB improvement.
• Beam Width
• Old: 124 asecs
  
• new: 122 Asecs
• PolA,B separate: old, new receiver performance (.ps) (.pdf)
• The gain,Tsys, and SEFD were computed separately for polA and polB (I+Q)*.5, (I-Q)*.5
  
• Page 1:
• Frame1,2: Gain polA, polB
• Fame 2,4: Tsys polA,polB
• Page 2: sefd polA,polB
  

Summary:

    The table below holds the values for polA and polB measured at za=10deg. If the two sources differed by a lot, then the values for  3C138 were used.

• Moving the receiver into focus in the Z direction (focus) will improve the gain at low za .. since the elevation rails are low at low za.
  

06dec12: compare calibration runs with new rcvr in focus.

• oct12: with the old receiver (set _1)
  
• 23nov12: new receiver out of focus in z (set _2)
• 06dec12: new receiver in focus (set_3)

Plotting the calibration results from each run separately

• Each set has 3 pages of plots:
• page1: gain, Tsys, sefd, beamwidth
• page2: coma, 1st sidelobe, eta , eta + 1st sidelobe
• page3: pointing errors.

• Set_1:Calibration runs old receiver (.ps) (.pdf)
• Set_2:Calibration runs with new receiver (but out of focus) (.ps) (.pdf)
• Set_3: Calibration runs with new receiver in focus (.ps) (.pdf):

Over plotting the 3 sets of calibration data:

The results from the 3 calibration runs are over plotted.(.ps) (.pdf):

• Page 1: gain,Tsys,sefd, average beam width for all sources.
• Black _01 is the old receiver
• Red _02 is the new receiver out of focus
• Green _03 is the new receiver in focus.
• B1040+123 was excluded because it looks like it's flux incorrect at 2380 Mhz.
• Tsys for the new receiver is about 3K lower. This is mainly from polB temp getting better,.
• Page2: Use B0518+165 (3C138) to compare the 3 datasets.
• B0518+165 was included in all 3 datasets.
• The values from the 2nd and 3rd  datasets were interpolated (in azimuth) to the positions of data set 1.
• This was to remove and difference because the samples may have been taken at different az,za's.
• Top: Gain:
• The new receiver gain (in focus) is about 10K/Jy for za's out to 15deg.
• Averaging over all data, the in focus gain is about 8% better than the new receiver out of focus.
• For za's <15 degrees the increase was > 10%.
• The large improvement is because the receiver is too low at low za (from the shimming).
• Middle/bottom: pointing error for B0518+165 for the 3 datasets (vs za).
  
• The az and za error has shifted down by about 10asecs
• The rise,set az error difference decreased when the receiver was moved into focus.
• Page 3: over plot the pointing error for the new receiver out and in focus.
• Using all the new receiver data the pointing offsets are:
• az -10.3 asecs
• za: -8.83 asecs
• We probably need to take some more sbn data (in focus) before correcting for these offsets.

Summary:

• moving the receiver into focus improved the gain by 8% over the entire za range.
• For za's < za=15 the gain improved by > 10%.