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Sections:

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History:

• 
  
• 02mar20 sbn back up. polB lna is bad . will have to live with high tsys till we get a replacement
  
• 17feb20 sbn down to lab  to check polB amp
  
• 27nov19: ports omt switched so oc comes out on chan A downstairs (see figure)
• 26apr19 : polB starts to rise. 04 aug19 jumped more. continued deteriorating till 17feb20 when it was found that amp was bad. need a replacement.
  
• 01may18  New gain curve installed (after maria).
  
• 09feb18: 15 db pad between rf filter chassis and postamp chassis removed.
  
• 08feb18: 120MHz rf filter replaced with 35MHz rf filter.
  
• xxjul14:polB amp (in the dewar) sband hi, was replaced by a new chalmers amp.This is polA on the outside.
  
• 01aug13: first stage of amps (both pols) burned up..
• had an sband experiment. ao19 was installed. many receivers taken down. When trying to bypass the shutters for the missing receivers, they reversed open and closed. So the tx transmitted with the shutters open.
• polA in the dewar was replaced with the spare sbn chalmers amps
• polB in the dewar was replaced one of the sbh amps
• The cables from amp to dewar output are swapped...so
• polAAmp (sbn spare) is polB outside
• polBAmp (sbhi amp) is polA outside.
  
• 13jan13: updated pointing offsets (after focus move).
  
• 26nov12: sbn moved up 1.2 inches along focus. (date may have been 28)
  
• 20nov12: cal values fir new sbn receiver  installed
  
• 09nov12: circulator postamp chassis was reversed.
  
• 28oct12: new sbn receiver installed. sbTx horn also replaced.
  
• 15mar06: sbn cal values remeasured at 2380 and 2280. Installed 10apr06, backdated to 14oct03.
• 14oct03 turnstile stubs switched. Also reversed  rf cables so polA is still polA downstairs. This is to put the "better" amplifier for the OC echo for the radar experiments.

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Calibration measurements:

Measurement by date

20may20: system performance for venus run declination.

Gain curve after maria using nov17 - mar18 data set.

    The telescope performance was degraded after the passage of hurricane maria (more info).
x102 calibration data 01nov18 through mar18 was used to generate a new gain curve (the previous gain curve was done in feb04). The 01nov17 through 12nov17 data was also used to generate the new pointing model after maria. The pointing could have been off a little, but the gain measurement should be ok (since we do spider scans of +/- 3 beams).

The plots show the data and gain fit (.ps) (.pdf):

• Page 1: measured gain
  
• top gain vs za
• bottom: gain vs az
• Page 2: az,za plot of gain
  
• The length of each arrow is proportional to the gain
• the rotation angle is also proportional to the gain:
  
• 0deg = 8 K/Jy
• 90deg = 6 K/Jy
• 180 deg= 4 K/Jy
• The east side of the dish shows lower gain.
• spider scans with no tiedown tension, or with the platform out of focus were excluded.
• The blue source: J1042+120 (at dec of 12 degrees) is an outlier.
  
• This source, and 3 other outlying scans were also excluded from the fit.
• Page 3: the gain fit vs za
• The red * are the input data
• the black + are the computed fit values
• The lines at the bottom show the coefficients for the fit:
• gain= C0  + C1*za + C2*(za-14)^2 + C3*(za-14)^3 +
•            C4*cos(az) + C5*sin(az) + c6*cos(2*az) + c7*sin(2*az) +
•            C8*cos(3*az) + C9*sin(3*az)
• The coef: c2,c3 are only used for za >= 14 deg.
• The fit rms is .41 K/Jy.
• Part of this is the model not fitting the data
• Another portion is the fluxes for most  sources also have errors (say 5% or more). 
• Page 4:  gain fit residuals   vs za and az
• The residuals are computed as : (measuredGain  - FitGain).
  
• top: fit residuals vs za
• bottom: fit residuals vs az
• Each source is plotted in a different color/symbol.
• The larger residuals at low za is common. The azimuth must swing pretty fast when doing a spider scan at low za's.
• Page 5: arrow plot of fit residuals.
• In this case, the arrows are constant length (since the residual can go to zero and wouldn't show up..)
• The angle from north gives the size of the residual

• angle From North (deg)	Data - Fit K/Jy	Notes
  0	0	fit = data
  +90 CW	+1K/Jy	fit < data
  +180 CW	+2K/Jy	fit < data
  -90 CCW	-1 K/Jy	fit > data
  -180 CCW	-2 K/Jy	fit > data

  
  
• So Clockwise has fitValue less than the MeasuedValue
• Counter Clockwise has fit greater than data.
• The green trace for B0824+294 on the lower right is CCW so the fit is overestimating the measured values.

    The gain curves were installed in the idl locations on 01may18 (#gain)

• The idl routine gainget(az,za,freq,rcvrnum,gainval,date=date) will compute the gain as a function of az and za
• For sbn the rcvr number=12
• the frequency was only measured at 2380 MHz (narrow and feed).
• If no date is given, then the most recent curve is used
• the date format is date=[year,dayNumberOfYear]

Compare pre and post maria gain curves:

    The gain curves for before and after maria were computed and then over plotted.

• the gain was computed at za = 2 to 19 deg in 1 deg steps
• this was done for azimuth angles: 0,60,120,180,240,300 degrees

• The black trace is the gain curve before maria
• the red trace is the gain curve after maria
• the vertical blue lines separate the gain vs za 2..19 for each set of azimuths.
• All of the post maria za strips are lower than the pre maria.
• within the post maria za strips,
• the eastern part of the dish has lower gain.. az=60,10,180 deg

processing: x101/sbn/may18/cmpgainfit.pro

Mar03 to Feb04  fit GAIN CURVES to calib data.  (top)

    A gain curve was fit to the sbn gain data  taken between 01mar03 and 29feb04.This data is described below.The plots show the gain data (black) and the fits (red) for 2380 MHz.This gain equation was installed on 09mar04.

• Fig 1 shows the az,za distribution for the data. The fit uses a linear fit out to a za of 14 degrees. Above 14 degrees it includes a za^2 and za^3 term. It also has 1az, 2az, and 3az sin, cos terms.
• Fig 2 top plots the gain data and the fit to za.  The fit equation is plotted with the sigma for the fit (in K/Jy). T
• Fig 2 bottom plots the fit residuals (data-fit) vs za.

    The routine gainget() or corhgainget() will now return the sbn gain for data taken after 01mar03 using this equation. The coefficients can be found in the ascii file  data/gain.datR12 (this is provided in the AO idl distribution for correlator routines). You can also find a copy of it at AO in /home/phil/idl/data/gain.datR12.

mar03 thru feb04 : System performance of data used to compute gain curves.  (top)

Fig 1 shows the distributions on the dish of the measurements.

Fig 2 has the Gain in Kelvins/Jansky. This relies on the cals and the source flux. Ths  next plot is Tsys vs za in Kelvins followed by the SEFD  (System Equivalent Flux density) in Janskies / Tsys. At the bottom is the average beam width in arc seconds.

Fig 3 plots the coma parameter, first sidelobe height below the peak, the main beam efficiency, followed by the main beam + 1st sidelobe beam efficiency.

Fig 3 has the pointing errors in az,za, and total (added in quadrature) for the data.

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Miscellaneous section.

01jul05 dewar warms up during radar run

13oct04 1.2 Hz total power ripple.

• shutter closed
• upstairs transfer switch crossed
• 260 IF used
• detect the 100 MHz band with a  20 usecond time constant. Do this separately for polA and polB.
• Sample the data at 10 usecs.

• Top figure. This is total power versus time for polA (black) and polB (red). The polarization's are referred to the dewar (not the downstairs signal since the xfer switch was in). The data was smoothed to 10 milliseconds. You can see the jumps in polB. It is not a sine wave. The signal stays low for .55 seconds and then jumps up (about 2% Tsys) for .28 seconds. The entire duration is .83 seconds or 1.2 Hz.
• Bottom Figure:  The 48 seconds of 10 usecond  sampled data was transformed and then the magnitude taken. There are a set of spikes spaced at .6 Hz (with a few harmonics missing).

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