2. Antenna Structure

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2.5 Specification Summary

2.5.1 Observing conditions

 

Parameters

Specifications

Precision

Wind, continuous

Wind, gusts

< 25 km/h

20 30 km/h

Sun Absent
Precipitation Absent
Temperature -25 30 C
Humidity < 90 %

Normal

Wind, continuous

Wind, gusts

< 65 km/h

50 80 km/h

Precipitation Absent
Temperature -30 50 C
Humidity < 100%
Survival Wind 200 km/h
Precipitation < 5 cm/h snow
Seismic 0.3 g horizontal

Tab. 2.5 : Observing conditions

In survival conditions, and when not in use, the antenna must be settled at 90 elevation and 180 azimuth (stow position).

2.5.2 Surface Accuracy

Structural Elements

(RSS mm)

90 El

(RSS mm)

60 El

Primary reflector panels 0.4 0.4
Secondary reflector panels 0.35 0.35
Gravitational deformation 0.58 0.19
Total surface accuracy 0.8 0.6

Tab. 2.6 : Surface accuracy at 90 and 60 elevation

To estimate the phase error from the surface accuracy, the following can be used :

δ = surface accuracy

λ = observation wavelength

Usually a maximum tolerable phase error is assumed as ε≈36≈0.63 rad , so that the minimum observable wavelength is

 

For the Medicina antenna :

2.5.3 Pointing accuracy

Observing condition Pointing accuracy

(rms arcmin)

Normal/Precision 0.13

Tab. 2.7 : Pointing accuracy

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