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Correlator  II: Implementation
D. Anish Roshi
The visibility measured by an interferometer is characterized
by the amplitude and phase of the fringe at different instants. For
simplicity first consider the output of a two element interferometer.
In the quasi monochromatic approximation the multiplier output can be
written as (see Chapter 4)

(9.0.1) 
where and are the voltages at the outputs of the
receiver systems of the two antennas, and are the
amplitude and the phase of the visibility and is the geometric delay.
The quantities required for mapping a source are and
for all pairs of antennas of the interferometer. These
quantities are measured by first canceling the term in
Eq. 9.0.1 by delay tracking and fringe stopping. In general,
one needs to know the amplitude and phase of the visibility as a function of
frequency. This chapter covers the implementation of a spectral
correlator to measure the visibility amplitude and phase. Further since
the delay tracking (and fringe stopping for some cases) is usually also
done by the correlator, these issues are also discussed.
Subsections
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