Measuring the cband cal values.

16may03

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:

Intro:

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: (..top)

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.

Figure 1 plots the cal Values measured the 3 different ways:

Black is cal polA, polB measured relative to the absorber.
Red is cal polA,polB measured relative to the sky.
Blue is cal polA, polb measured using the absorber,sky ratio.

Fig 2 fits a high order polynomial (red line 13th order) to the absorber and skyAbsorber measurements. The green crosses were used for the fit. The blue line is a cumfiltered version of each 25Mhz set. The cal values installed are computed from the red line.
Fig 3,4 shows the individual measurements : absorber, sky, skyAbsorber ratio.

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.

Fig 1. The entire frequency range 4000 to 6000.
Fig 2-4. The same data in 500 Mhz chunks.

The power levels during the measurements:

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

Fig 1. Top the power level measured at the fiber optic transmitter (the actual power is +20db more since a 20db coupler is used).
Fig 1.Bottom the power at the downstairs power meter (actual power is +20db more).
Fig 2. The 0Lag power (25 Mhz) normalized to the median value for all of the measurements. The figures are sbc1 thru 4. The large variation at the beginning and end is on the sky (where the cal value is a large fraction of tsys). The center part is on the absorber.
Fig 3. The same as figure 2, but the power counter data (50 Mhz that goes to the digitizer).

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/cbcal.pro

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

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:

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.
Fig 2 top plots the ratio of the cal/hcorcal for the high cals.

The horizontal blue, blacks 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 lines have diode2->polB through the 90 deg leg of the hybrid.
The purple,green lines have diode2->polA through the 0 deg leg of the 90 deg hybrid.
The black lines overlaying each data curve is a 13th order polynomial fit the to the data. The * are the frequencies that were used for the fit.

Fig 2 bottom is the same plots for the ratio of the low cals to the hcorcal.
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/cbcal.pro

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