sbw cal values measured 09jul04

Ratio of other cals to hcorcal tracking blank sky.
Compare tsys using old and new cal values.

Links to SECTIONS:
Measuring the high correlated cal using blank sky and absorber
Measuring the other cals on blank sky relative to the high correlated cal.

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Measuring the high correlated cal using sky and absorber: (top)

    The temperatures used in the computation were:
 

Tabsorber	298
Tsky+Tscattered	20 K
Treceiver	from test shack

    The sbw receiver has some frequency ranges that are unusable because of rfi. The cal measurements were done with the rfi filter bank filters in. The gaps in frequency of the data are where the largest rfi occurs.
    Each frequency band was measured 6 separate times on the absorber and 6 separate times on the sky. For each measurement the calon/off-1 spectrum was  computed.  A 2nd order polynomial was fit to the spectra for the 6 measurements of each bandpass (25 Mhz). All points with fit residuals above 3 sigma were thrown out. The total power for each 25 Mhz band was then computed masking out these bad points.
    A 4th order polynomial was fit to this data to generate the cal values (throwing out any data points greater than 2 sigma on the first iteration of the fit). The cal Value versus frequency plots show the results.

• Fig 1 is the measured cal value in deg K versus frequency. The colors are: Blue is measured using the sky and absorber ratio. Black is using just the absorber and red is using just the sky. The Top plot is polA and the bottom plot is polB. The dashed blue  line is the old cal values. The dash green line is the receiver temperature used (from the antenna test range measurement). The Tsky+Tscattered was adjusted so that the Cal from the sky agreed with the cal from the sky absorber ratio (polB sky looks about 1.5 Kelvins high so either the Trcvr is wrong or the scattered radiation is off).
• Fig 2 is a 4th order polynomial fit to the calAbsorber and calRatio measured values (it will be used to generate the cal value table). The green crosses were used for the fit. The dashed blue line is the cal values measured on the antenna test range. The purple line is from cumfiltering the 6 measurements.
• Fig 3 and 4 show the cal values for each measurement (polA, polB). The top plot has the 6 measurements on the absorber. The center plot shows the 6 measurements on the sky. The bottom plot is the absorber, sky ratio. The absorber measurements have more scatter then the sky measurements even though the sky measurements had more rfi. The time bandwidth product should have had an rms error of about .05 K.

•  Fig 1. This has the entire range of 1.7 to 3.1  Ghz. Top is polA, bottom is polB. Each pass through the frequency range is offset from the previous one for plotting purposes.
• Fig 2-3 has the  same data broken up into 500 Mhz sections.

    The final plot has the power levels during the measurements.

• Fig 1 top is the power at the upstairs fiber optic transmitter for all of the measurements. The spectral density for a
• Fig 1 center is the power at the downstairs if power meter.
• Fig 2 The power counters. They record the 50 Mhz as seen by the digitizer (before the digital filters).
• Fig 3 plots the 25 Mhz 9 level total power measured via the 0 lag of the correlator. A 25 MHz digital filter sits between the power counter of figure 2 and this measurement.

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Measuring the other cals using sky and the high correlated cal from above.  (top)

• hcorcal(on,off)
• hcal(on,off),hxcal(on,off),h90cal(on,off)
• hcorcal(on,off)
• lcorcal(on,off),lcal(on,off),lxcal(on,off),l90cal(on,off)
• hcorcal(on,off)

    The calOn/calOff -1  spectra was computed for each measurement (giving cal in units of calOff or Tsys).  Each of these 25 Mhz band passes was cumfiltered. This was done on the 3 loops of the same freq band (256 channels *2 numbers). The total power was computed and then the ratio of each cal value relative to the hcorcal was computed (via interpolation of the 3 hcorcal measurements). A 5th order polynomial was then fit to the data vs frequency. These values were used to generate the cals table (after multiplying by the hcorcal in kelvins). The figures show the other cals relative to Tsys and the hcorcal:

• Fig 1. This is the cal value as a fraction of Tsys for each of the cal types. The top figure has the high cals while the bottom figure shows the low cals. The lines with * are polB. The cal types where the same diode feeds the same polarization (polA horcal,hcal.. polB hxcal,hcorcal, etc) are in agreement. Since they were measured at different times, the weather was not having large affect on the data.
• Fig 2. The calType/hcorcal. The top has the high cals while the lower plot is the low cals.  The * are an 5th order fit to the data. Diode 1 (hcorcal) is twice as big as diodeB (the ratios are about .5).
• Fig 3. The hcorcal was measured 3 times in each set of 10 measurements. This graph plots the ratio of tsys for the 2ndHcorcal/1stHcorcal (red) and 3rdHcorcal/1stHcorcal (blue). The * have the cal on while the + have the cal off. Each frame is a different pass through the frequency range. These are the raw tsys values. There has been no cumfiltering done yet. If the + and * jump together, then it was Tsys that was changing. If the + and * jump differently then it could have been the cal value. The ratios have interpolated between the 3 hcorcal measurements.

• The top plot uses the old calvalues (only the high cals are plotted). Pol B is the dashed lines.
• The bottom plot uses the new cal values.  Day 135  was the date that the new cal  diodes were installed. The temperatures for polA and polB are now the same.