Measuring the cband cal  values.


 Links to sections:

The hcorcal measured values:
The spectra of (calon/caloff -1).
The power levels during the measurements.

Links to Sections:

Measuring the hcorcal
The ratio  of the other cals to the hcorcal:


    New diodes were installed on the cband system on 22apr03. On 25apr03 the cals were measured using absorber and tracking blank sky.  A ripple in polA cal pointed to a loose cable in the cal box. The cable was tightened on 05may03 and the cals were remeasured on 16may03.
    The correlator was configured as 25 Mhz by 1024 lags by 4 sbc.  4000 to 6000 MHz  was covered in 100 Mhz chunks (20 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 4000 to 6000  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 cband were:
Temperatures Used
Trcvr from amplifiers 8 K
Tomt orthmode transducer 4 K
Tabs absorber temperature 301 K
Tsky sky + scattered ground radiation 3 + 15=18K
Trcvr Tamp+Tomt 8 + 4 = 12K

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 4000 to 6000 Mhz (6 in total). Offsets have been added to each pass for plotting purposes.

The power levels during the measurements:

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

    All three methods give consistent values for 4300 through 5000 Mhz (of course I twiddled the value of Tsky for this to happen!). Outside this range the Cal values measured from Tsky do not agree with those from Tabs or the ratios.  This disagreement comes from using a constant Trcvr of 12K. calAbsorber, calRatio is not sensitive to the Trcvr while calSky is. When the red line drops below the other two, Trcvr in that region is higher than the 12K that was used for the computation.

processing: x101/030516/hcorcal/

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

    On 16may03blank sky was tracked with the cb 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 4000 to 6000 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 in the sequence, the cal on/off spectra was computed and then cumfiltered to remove 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. A 13th order polynomial was then fit to each curve to generate the cal values.
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.
  2. Fig 2 top plots the ratio of the cal/hcorcal for the high cals.
  3. Fig 2 bottom is the same plots for the ratio of the low cals to the hcorcal.
  4. Fig 3 shows how the hcorcal measurement varied for the 3 samples taken at each frequency. The 2nd (red) and 3rd (blue) hcorcal measurement were divided by the first hcorcal measurement (and then 1 was subtracted). Some of the slope is the change in Tsys with za (decreases at the start then increases at the end).
processing: x101/030516/othercals/