Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/~phil/hardware/powermeter/20120208_LadyBug_Attenuators_GD_CH.pdf Дата изменения: Thu Feb 9 19:11:11 2012 Дата индексирования: Tue Feb 5 03:20:46 2013 Кодировка: Поисковые слова: mdi

LadyBug Power Monitor - Attenuators

Document No. 430TX001, Rev. 001

LadyBug Power Monitor - Attenuators L. Quintero, A. Santoni, V. Iguina Arecib o Observatory Feb 8, 2012 1 Intro duction

43.00dB of the previous section. If we add this to the directional coupler attenuation, we will get 89.82dB total. We are correcting in the LabVIEW application (datalogger) for 89.80dB .

We measured -29.54dB m for CH, that give us 40.01dB total attenuation. Pretty close to the 39.95dB reference value. The measurement, plus the directional coupler This document shows reference values and rough mea- reference value, gives 90.01dB total attenuation. We are surements of the attenuators attached to the LadyBug using 90.02dB in the LabVIEW application. power sensors placed at the Gregorian Dome (GD) and Carriage House (CH). These attenuators are connected to the directional couplers attached to the waveguide. 4 Datalogger Power Measurements We are considering the following attenuation values for the directional couplers, GD: 46.7dB (measured at AO, The LabVIEW application shows the peak power in kiloWatts (kW). This is the default configuration, but difAug 2004) and CH: 50.00dB (reference value). ferent units can be selected (e.g. dB m). 2 Previous Measurements We applied a known signal (430M H z @ 5.06dB m) to the combination of attenuators (except directional coupler) and LadyBug sensors. We measured the peak power in kW using the LabVIEW application, and calculated the equivalent power value in dB m applied to first attenuator. We expect these results close to 5.06dB m (R&S FSH6 measurement). The measurements were taken on Feb 6, 2012 around 11:00am.

The attenuators were measured individually, except one, before installing the boxes at the platform during Summer 2010. Each attenuator has a label attached to it, and shows the values shown in Figures 1 and 2. There is not label for the 30dB attenuator for the Carriage House, but we expect an attenuation close to this value. According to these numbers, we expect total attenuation of We measured 0.1646k W for GD, this is equivalent to 43.00dB and 39.95dB for GD and CH, respectively. 52.16dB m1 . We are adding 89.80dB in LabVIEW, so this is -37.64dB m at the sensor. We measured 43.12dB for the three attenuators, therefore it is 5.48dB m at the first attenuator (30.04dB ). This value is pretty close to the expected 5.06dB m. We did the same procedure for the CH box. The LabVIEW display showed 0.3412k W , it is 55.33dB m. We are correcting for 90.02dB in LabVIEW, so at the sensor we have -34.69dB m. Adding the attenuators measurement, 40.01dB , we have 5.32dB m at the first attenuator (30dB ). This is also very close to the applied power.

Figure 1: Gregorian Dome Attenuators.

5 Figure 2: Carriage House Attenuators.

Conclusion

3

Total Attenuation

There is a slightly difference between the previous measurements of the attenuators in 2010, and the total attenuation measured during this exercise. We got 0.12dB and 0.06dB difference for GD and CH, respectively. The total attenuation values - including directional couplers - used in LabVIEW, match with the measurements and reference values cited in this document. The difference between these values is 0.02dB and 0.01dB for GD and CH, respectively. We got differences in the last measurements - calculated
1

We measured (3 Feb, 2012, 4:00pm) the total attenuation of the circuits of Figures 1 and 2, applying a 430M H z at 10.47dB m signal and taking the measurements at the end of the attenuators. All these measurements were taken with the Rohde & Schwarz FSH6 Handheld Spectrum Analyzer with the R&S FSH-Z1 Power Sensor accessory. We got -32.65dB m at the end of the GD attenuators, so it give us 43.12dB attenuation, pretty close to the Arecibo Observatory

P

dB m

= 10log10 (P

mW

/1mW )

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Release: February 8, 2012


LadyBug Power Monitor - Attenuators

Document No. 430TX001, Rev. 001

power at the first attenuator - of 0.42dB and 0.26dB for GD and CH, respectively. This is not a dramatic difference, but it is required a calibration procedure in order to reduce the uncertainty. This could be caused by differences between instrument readings (offsets?, calibration?), and connectors coupling. Just for information purposes, on Jan 2010 we compared the LadyBug sensors available at AO with one of our Agilent E4418B power meters. You can see the results in Table 1. The sensors installed at the platform are the LB480A (pulse profiling sensors); GD: S/N 98415; CH: S/N 97404.

Figure 3 shows the linear regression between the LB480A sensors and the Agilent E4418B power meter. Both sensors show a good correlations along the scale, and just 0.12dB and 0.06dB offset for GD and CH, respectively. It should be noted that we do not know anything about the calibration status if the E4418B.

Table 1: LadyBug Sensors comparison, Jan 20, 2010. We used the Agilent N5181A to generate different power levels from -60dB m to LadyBug sensor limits are from -60dB m the measurements were taken with 100 the instruments. a 430M H z at 10dB m. The to 20dB m. All averages in all

Figure 3: LadyBug Sensors plot. Arecibo Observatory Page 2 of 2

Release: February 8, 2012