Measuring the ratio of the other cals to the hcorcal

checking the cal 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)

Measuring the hcorcal: (..top)

Trcvr | from hilltop measurements | 11 to 18K |

Tabs | absorber temperature | 301 K |

Tsky | sky + scattered ground radiation | 3 + 15=18K |

- 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.

- 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.

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

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%.

Checking the cal values (..top)

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