= Residual phase of a tracked east-west interferometer
{title2=$\delta\phi\simeq2\pi b\alpha\cos\theta/\lambda$}
For an east-west baseline $b$ and phase-centre zenith angle $\theta$ in its vertical plane, path compensation subtracts $b\sin\theta$. An offset $\alpha$ leaves $\delta\ell=b[\sin(\theta+\alpha)-\sin\theta]\simeq b\alpha\cos\theta$. The complex correlation therefore has phase $2\pi b\alpha\cos\theta/\lambda$, up to receiver-order convention. Equal cable lengths do not remove this sky-dependent path difference.
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