sbw cal values measured 09jul04


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.
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.

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

    The sband wide diodes were replaced on 14may04 (dayno 135). The high correlated  cal value (diode 1 going to polA and polB)  was measured 29jun04 (on absorber) and on 09jul04 (on sky) using  the sky/absorber technique. The telescope tracked  blank sky and used 3 second cal on/offs.
    The cals values had also been measured at the receiver test shack in sep01. These measurements included the measurement of Treceiver across the band. These Treceiver measured was used in the 09jul04 reduction.

    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.

    The spectra of calOn/Caloff-1 for the 6 sky measurements  shows the spectra for the on sky measurements. 100 Mhz chunks at a time were taken. The dotted vertical lines are the edges of the 25 Mhz band passes.     There are ripples at the low end of the spectra. The dips at the high end are resonances in the omt.

    The final plot has the power levels during the measurements.

processing: x101/040709/hcorcal/,,,

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 measured relative to the high correlated cal. This was done on 09jul04 after the hcorcal sky tracking was done. Three  passes were done through the frequency range.  The sky was clear the entire time.  The cal sequence was:     100 Mhz at a time was measured (4 by 25Mhz) going from 1700 to 3100 Mhz. The cal was cycled on/off for 3 secs at each step.  The entire frequency range was repeated 3 times.

    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:

Tsys is measured daily at 2290 Mhz for sbw.The final plot shows the tsys values using the old and new cal values. New cal diodes were installed on 14may04. They were calibrated on 09jul04. The new cal values were installed on 18jul04 and backed dated to become active on 14may04. The aoidl routines will now use these values for data taken after 14may04. The data can be found in the file : aodefdir()/data/cal.datR7 (/pkg/rsi/local/libao/phil/data/cal.datR7 or in /share/obs4/rcvm/cal.datR7.