Bipolar gradients during the variable evolution period, t1, are usually applied to minimize radiation damping effects on samples dissolved in H₂O.

Easy implementation on AVANCE spectrometers equipped with pulsed field gradients.

The standard way to implement a variable evolution delay in a pulse program is:

... d0 gron0 d0 gron0*-1 2u groff ... id0

in which d0 is the variable evolution delay (in seconds) and in0 is the value to be incremented each time id0 is found. nd0 must be set to 2.In 3D experiments, d10 is used to define the second variable evolution delay similarly as described for d0.

gpz0 defines the intensity of such gradients (usually 2-3%).

Also see: fixed free-evolution delay.