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Gain calibration

The time required per scan on the gain calibrator (also referred to as the phase calibrator) is also given by Equation 7.1, except that a minimum time of 2 seconds is enforced. The phase calibrator flux is always assumed to be 1 Jy and the required antenna-based SNR is 20 over a bandwidth of 2 GHz.

The phase calibration cycle time is calculated using

\begin{displaymath}
t = \max \left[ \left(\frac{2}{v_\mathrm{wind}}\right)\left...
...\sec{Z}}}\right)^{\frac{1}{\alpha}}, 15~\mathrm{sec}\right]
\end{displaymath} (7.2)

where $Z$ is the zenith angle and $\alpha$ the exponent of the phase fluctuation structure function (defined to be the median value at the AOS = 0.6). The phase fluctuations themselves are given by $\eta$, where this is equal to 2.9 for bands 6 and below, and to 6.1 for bands 7 and above. The wind speed is taken to be the site average of 10 m/s. As this formula is only valid up to 5 minutes, cycle times longer than this are set to this value.



The ALMA OT Team, 2014 May 21