# Difference between revisions of "Polarization Mixing Correction (Old)"

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The newer 2.1-m antennas [Ants 1-8 and 12] have AzEl (azimuth-elevation) mounts, which means that the crossed linear feeds have a constant angle relative to the horizon (the axis of rotation being at the zenith). The older 2.1-m antennas [Ants 9-11 and 13], and the 27-m antenna [Ant 14], have Equatorial mounts, which means that the crossed linear feeds have a constant angle with respect to the celestial equator, the axis of rotation being at the north celestial pole. Thus, the celestial coordinate system is tilted by the local co-latitude (complement of the latitude). This tilt results in a relative feed rotation between the 27-m antenna and the AzEl mounts, but not between the 27-m and the older equatorial mounts. This angle is called the "parallactic angle," and is given by: | The newer 2.1-m antennas [Ants 1-8 and 12] have AzEl (azimuth-elevation) mounts, which means that the crossed linear feeds have a constant angle relative to the horizon (the axis of rotation being at the zenith). The older 2.1-m antennas [Ants 9-11 and 13], and the 27-m antenna [Ant 14], have Equatorial mounts, which means that the crossed linear feeds have a constant angle with respect to the celestial equator, the axis of rotation being at the north celestial pole. Thus, the celestial coordinate system is tilted by the local co-latitude (complement of the latitude). This tilt results in a relative feed rotation between the 27-m antenna and the AzEl mounts, but not between the 27-m and the older equatorial mounts. This angle is called the "parallactic angle," and is given by: | ||

− | <center><math>\chi = \arctan(\cos\lambda \sin | + | <center><math>\chi = \arctan(\cos\lambda \sin A, \sin\lambda \cos E - \cos\lambda \sin E \cos A)</math>,</center> |

+ | |||

+ | where <math>\lambda</math> is the site latitude, <math>A</math> is the Azimuth angle [0 north], and <math>E</math> is the Elevation angle [0 on horizon]. | ||

= Status of tests = | = Status of tests = |

## Revision as of 15:18, 20 October 2016

# Explanation of Polarization Mixing

The newer 2.1-m antennas [Ants 1-8 and 12] have AzEl (azimuth-elevation) mounts, which means that the crossed linear feeds have a constant angle relative to the horizon (the axis of rotation being at the zenith). The older 2.1-m antennas [Ants 9-11 and 13], and the 27-m antenna [Ant 14], have Equatorial mounts, which means that the crossed linear feeds have a constant angle with respect to the celestial equator, the axis of rotation being at the north celestial pole. Thus, the celestial coordinate system is tilted by the local co-latitude (complement of the latitude). This tilt results in a relative feed rotation between the 27-m antenna and the AzEl mounts, but not between the 27-m and the older equatorial mounts. This angle is called the "parallactic angle," and is given by:

where is the site latitude, is the Azimuth angle [0 north], and is the Elevation angle [0 on horizon].