## The notion of phase cycle

The phase cycles or phase programs allow to :

-choose the relevant signals and to neglect these ones which do not contain information and which, eventually, are susceptible to hide some other useful signals.

-discriminate the sign of the frequencies in the fl dimension.

-compensate the inhomogeneities from one or several impulsions in the sequence,

-to achieve an optimal quadratic detection in the
f2 axis^{[1]}. (5)

Any impulsion in a sequence has its own phase cycle which may be more or less complex.

The ideal number of scans must be a multiple of the phase number of the longer cycle.

For a better understanding of this method, a standard nomenclature has been defined.

### Example : The cyclops cycle

= x, y, -x, -y. 0, 1, 2, 3.

This cycle involves the accumulation of a multiple of 4 numbers between each free precession.

The first impulsion occurs around the x and the emission will occur in the y axis, the third impulsion along the - x and the reception in -y, etc...

There are other variations of this cycle like the following:

= x, y, -x, -y, or 0, 2, 1, 3.

Or still : = x, x, -x, -x, y, y, -y, -y or 0, 0, 2, 2, 1, 1, 3, 3.

This last one implies a multiple of 8 transient cycles in the accumulation.