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Äàòà èçìåíåíèÿ: Wed Mar 1 18:52:04 2006
Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 20:04:41 2007
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Ïîèñêîâûå ñëîâà: asteroid

Measuring the cband cal values.

25apr03

Links to the plots:

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

Intro:

New diodes were installed on the cband system on 22apr03. On 25apr03 the cals were measured using absorber and tracking blank sky. 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 9 times on absorber and 9 times on the sky. See measuring cals on the telescope using sky and absorber for a more detailed description.

NOTE:

After taking the data, the spectrum of the cal showed a ripple in polA. This turned out to be a loose cable in the cal box. On 05may03 the problem was found and corrected. The cal values measured here were installed because of a calibration run on 25apr03. There was no other cband data taken between 22apr03 and 05may03.

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	302 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 shows cal polA, polB measured relative to the absorber.
Red shows cal polA,polB measured relative to the sky.
Blue is cal polA, polb measured using the ratios of the absorber and sky measurements.

Fig 2 is the cal value from the absorber and ratio measurement (averaged over each 25Mhz band) with no cum filtering. The red line is a high order (13th) polynomial fit to the data. This was used to generate the cal values that were installed.
Fig 3,4 plot the cal values for each of the measurements: absorber, sky, and 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 (9 in total). Offsets have been added to each pass for plotting purposes. A 1 Mhz ripple is a delay of 1 usec or a down and back distance of 150 meters. The 90 MHz ripple in polA would be 150/90. * .6 = 1 meter (.6 is the velocity of light in the cables). Since the ripple is in polA and not polB (using the correlated cal), the loose cable is after the power splitter for diode1.
The cable was tightened 05ma03 and the cals were remeasured.

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).

processing: x101/030425/cbcal.pro

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