  The paper describes the multiple rotating frame technique for designing
modulated rf-fields, that perform broadband heteronuclear decoupling in
solution NMR spectroscopy. The decoupling is understood by performing a
sequence of coordinate transformations, each of which demodulates a component
of the Rf-field to a static component, that progressively averages the chemical
shift and dipolar interaction. We show that by increasing the number of
modulations in the decoupling field, the ratio of dispersion in the chemical
shift to the strength of the rf-field is successively reduced in progressive
frames. The known decoupling methods like continuous wave decoupling, TPPM etc,
are special cases of this method and their performance improves by adding
additional modulations in the decoupling field. The technique is also expected
to find use in designing decoupling pulse sequences in Solid State NMR
spectroscopy and design of various excitation, inversion and mixing sequences.
