Lbw cal values measured 06mar03

28mar03

Links to PLOTS:
hcorcal value versus freq from sky and absorber
spectra of hcorcal on/off-1 on sky
power levels during hcorcal measurements

Ratio of other cals to hcorcal tracking blank sky.

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.

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

The high correlated cal value (diode 1 going to polA and polB) for lband wide was measured 06mar03 on the telescope using the sky/absorber technique. The telescope tracked blank sky and used 3 second cal on/offs. The data was taken with the radar blanker on for both the sky and absorber.
The cals values had also been measured at the receiver test shack in feb03. These measurements included the measurement of Treceiver across the band. The Treceiver measured was used in the 06mar03 reduction.

The temperatures used in the computation were:

Tabsorber 304 K

Tsky 5 K

Treceiver from test shack

Tscattered 15 K

Each frequency band was measured 6 separate times on the absorber and 9 separate times on the sky. For each measurement the calon/off-1 spectrum was computed. A 3rd order polynomial was fit to this data to generate the cal values (throwing out any datapoints greater than 2sigma on the first iteration of the fit). The calValue 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 red line is the cal value measured at the antenna test range.. The dash green line is the receiver temperature used (from the antenna test range measurement). The cal value from the sky does not agree very well with the values from the absorber and absorber, sky ratio.
Fig 2 is a 3rd 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 red line is the cal values measured on the antenna test range. polB 1320-1420 data was not used as well as some polA points at lower frequency.
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 9 measurements on the sky. The bottom plot is the absorber, sky ratio. Pol A on absorber has jumps in the first 100 Mhz while polB has jumps 1300-1400 Mhz on the sky.

The spectra of calOn/Caloff-1 for the 9 sky measurements shows the spectra for the on sky measurements. 100 Mhz junks at a time were taken. Since the radar blanker was on, pol A is clean in the 1300 to 1400 Mhz band. Pol B has some troubles in this region. Since pol A was working, we must have been tracking and the blanking must have been working. The only thing i can think of is that polB was going into saturation from the radar and was not recovering within the 400 usec blanking period. The 11db amp in the filter bank was before the filters so there was 71 db gain (40 dewar, 26-6 pol box, +11 amp) before any attenuation.

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. There were 108 records on the absorber, 3*(108)=324 records on the sky and then a final 108 records on the absorber. The large dips are at the lowest frequency 1120-1220 where the bandpass filter is cutting off half the band. The spectral density was probably ok for the fiber optic transmitter.
Fig 1 center is the power at the downstairs if power meter.
Fig 2 plots the 50 Mhz band (via the power counters) that is input to the correlator 8 bit a/d converter. Top to bottom is correlator board 1 (first 25 MHz of 100 MHz section) through board 4 (last 25 MHz of the 100 Mhz section). The level has been divided by the median value (the scale is linear in power). The jumps in middle are larger since the cal is a larger fraction of Tsys when on the sky (the central 324 records).
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. The rfi does not look as bad.

processing: x101/030306/hcorcal/lbwinp.pro,lbwcal.pro,lbwspec.pro,lbwdiag.pro

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

The high correlated cal was measured above using sky and absorber as the hot and cold load. The other cals were then measured relative to the high correlated cal. Blank sky was tracked and the following cal sequence was run:

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)

100 Mhz at a time was measured (4 by 25Mhz) going from 1120 to 1720 Mhz. The cal was cycled on/off for 3 secs at each step. The entire frequency range was repeated 6 times.
The calOn/calOff -1 spectra was computed for each measurement (giving cal in units of calOff or Tsys). Each of these 25 Mhz bandpasses was cumfiltered. This was done on the 6 loops of the same freq band (256 channels *6 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 measurements). These values were used to generate the cals table (after multiplying by the hcorcal in kelvins). No polynomial fit to the data was done. 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) all track extremely well even thought they were different measurements.
Fig 2. The calType/hcorcal. The top has the high cals while the lower plot is the lowcals. The frequency ripple in the high cal ratios is probably from the 90 deg hybrid (diode2 ->). The low cal diode1 ratios have a large sine wave. This is probably coming from the directional coupler used to generate the low cal from the high cal.
Fig 3. The hcorcal was measured 3 times in each set of 10 measurements. This plot shows how well the cal on and cal off values repeated. Most of the jumps include the * (calon) and + (caloff) so tsys was moving , not the value of the cal.

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