Measuring the sband high  cal  values.


 Links to sections:

Measuring the hcorcal
Measuring the ratio of the other cals to the hcorcal
checking the cal values

Links to plots:

The hcorcal measured values:
The spectra of (calon/caloff -1).
The power levels during the measurements.
The ratio  of the other cals to the hcorcal:
Tsys for 2004 using old and new cals

Intro:  (

    The sbh diodes were replaced on 13feb04. On 9mar04 the  diodes were calibrated using the sky and absorber. The correlator was configured as 25 Mhz by 256 lags by 4 sbc.  3000 to 4000  MHz  was covered in 100 Mhz chunks (10 steps). At each step a 3 second integration with the hcorcal on was followed by a 3 second integration with the cal off. The frequency range 3000 to 4000  was covered 6 times on absorber and 6 times on the sky. After this the "other cals"  were measured relative to the hcorcal while tracking blank sky. See  measuring cals on the telescope using sky and absorber for a more detailed description.

Measuring the hcorcal: (

The temperatures used for sbh were:
Temperatures Used
Trcvr from hilltop measurements 11 to 18K
Tabs absorber temperature 301 K
Tsky sky + scattered ground radiation 3 + 13=16K

The hcorcal measured values:

    This shows the results of the measurements.

The spectra of (calon/caloff -1):

     The spectra for the  cal (calOn/caloff -1) for the data taken on the sky is shown in the plots. Each color is a different pass through the frequency range 3000 to 4000 Mhz (6 in total).  Offsets have been added to each pass for plotting purposes. The top plot is polA, the bottom plot is polB.

The power levels during the measurements:

    The power levels during the measurements are shown. Black is pola and red is polB.

    The absorber and sky/absorber ratio give consistent results. They were used to compute the cal values. The variation in Calsky comes from the value of Trcvr used. The error in Trcvr is a small fract of Tabs and it is divided out using the Y factor, so these two agree. The error in Trcvr is a larger fraction of Tsky and causes calSky to jump around.

processing: x101/040309/hcorcal/

Measuring the ratio of the "other" cals to the hcorcal.   (

    On the same day (09mar04) blank sky was tracked with the sbh receiver. A sequence of 10 cal on/off measurements were done using the correlator configured as 25 MHz x 4 boards. The sequence was (hcorcal, hcal, hxcal, h90cal, hcorcal, lcorcal, lcal, lxcal, l90cal, hcorcal). This sequence was repeated covering 3000 to 4000 Mhz. The hcorcal was measured using the sky and absorber (see above). The ratio of the "other" cals was then  computed relative to the hcorcal (see measuring cals on the telescope using sky and absorber ).
    For each cal at each frequency step, the cal on/off spectra was computed and then cumfiltered over the 25 MHz frequency and the 3 repeated loops to remove any "obvious" rfi. The ratio with the hcorcal was then computed by interpolating between the 3 hcorcal measurements. The interpolation was used since  each cal is measured relative to the calOff (or tsys) and tsys varies as we track blank sky.
The ratio  of the other cals to the hcorcal is shown in the plots:
  1. Fig 1 top shows the high cals measured relative to tsys versus frequency. The * are pol B. The vertical lines show the 100 Mhz steps. There were 4 25 Mhz measurements at each frequency setting. Some of the cal sizes track each other since they come from the same diode (e.g.. polA hcorcal:hcal,  hxcal:h90cal, polB hcorcal,h90cal). The bottom plot has the low cals. The bump at 3200 Mhz and at 3600Mhz is seen to be only in diode 1.
  2. Fig 2 top plots the ratio of the cal/hcorcal for the high cals. The horizontal red, black line have diode1->polA and diode 1->polB. This is the same configuration for the hcorcal so the ratio is close to 1. The red (bright,dark)  lines have diode2->polB through the 90 deg leg of a hybrid while the green violet lines have diode 2 -> polA through the 0 deg leg of a hybrid.
  3. Fig 2 bottom is the ratio of the low cals to the hcorcal.  The non zero slope for the ratio of diode1->polAL / diode1->polAH is probably the frequency response of the 10db coupler used to create the low cal.
  4. Fig 3 show how the hcorcal measurement varied for the 3 hcorcal samples taken at each frequency. The 2nd (red) and 3rd (green) hcorcal measurement were divided by the first hcorcal measurement (and then subtracted 1). These values stay within .5%.
The ripple in the cal value that has a peak at 3200 Mhz and 3600 Mhz is coming from diode 1. It is before the switch in the postamp box that selects diode 1 or diode 2 to be sent to a particular polarization. It may be a bad match back at the diode.
processing: x101/040309/othercals/

Checking the cal values  (

    The tsys measurements for 2004 were recomputed using the new cal value at 3500 Mhz. The plot shows the Tsys values for 2004 using the may03 cal values (top) and the mar04 values (bottom).