Measuring the sband high cal values.

09may03

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 2003 using old and new cals

Intro: (..top)

The sbh diodes have been drifting slowly with time since their installation in march of 2002. On 9may03 the old diodes were recalibrated 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: (..top)

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 + 15=18K

The hcorcal measured values:

This shows the results of the measurements.

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

Black shows cal polA, polB measured relative to the absorber.
Red shows cal polA,polB measured relative to the sky using Trcvr from the hilltop measurements.
Blue is cal polA, polb measured using the ratios of the cals with absorber and sky.
Violet: cal from Tsky but using Trcvr=12K for the entire band.

Fig 2 fits a 3rd order polynomial to the cal value. The top plot is polA, the bottom plot is polB

Green are the data values used for the final fit
Black are values gt 2sig from the original fit.

Fig 3 plots the cal values vs freq for polA averaged over the 25 Mhz bandwidths. The color are the 6 separate measurements. Top to bottom is the cal measured using: the absorber, the sky, and the sky absorber ratio.
Fig 4 polB version of fig 3.

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.

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 0 Lag power (25 Mhz) normalized to the median value for all of the measurements. The figures are sbc1 thru 4. The large variation at the end is on the sky (where the cal value is a large fraction of tsys). The first part is on the absorber.
Fig 3. The same as figure 2, but the power counter data (50 Mhz that goes to the digitizer).

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.

The cals from Tsky are telling us something about the receiver temperature. Using the Trcvr measured on the antenna range ( the hilltop) makes Calsky at low frequency equal to CalAbs,CalRatio. So Trcvr is going up to 17 K at low frequency. For higher frequencies, Trcvr =12K does a better job at making calSky=calAbs than the Trcvr measured on the hilltop (especially for polB). So the receiver temperature above 3400Mhz probably does not increase as fast as the green curve would have it.

processing: x101/030509/hcorcal/sbhcal.pro

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

On the same day (09may03) 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:

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 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.
Fig 2 bottom is the ratio of the low cals to the hcorcal. The non zero slope for the ration of diode1->polAL / diode1->polAH is probably the frequency response of the 10db coupler used to create the low cal.
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 .3%.

processing: x101/030509/othercals/sbhcal.pro

Checking the cal values (..top)

The tsys measurements for 2003 were recomputed using the new cal value at 3500 Mhz. The plot shows the Tsys values for 2003 using the mar02 cal values (top) and the may03 values (bottom). Note that the vertical scales are different. The new cal values have brought down from (50,38) to (28,27). Using the new cal values you can still see a drift of Tsys for 2003. So the drifting has continued during 2003.

x101/030509/othercals/chksbwcal.pro

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