The modification described by A. G. Redfield and S. D. Kunz (1975) for a dual-channel NMR quadrature detection scheme is used in a single-channel spectrometer by stepping the actual ref. phase of the receiver by 90 Deg between adjacent sample points according to an analogous 4-step cycle. The resulting free induction signal is transformed and phase-cor. by the std. software of a conventional single-channel spectrometer. The modification provides 4 selectable phases of 0, 45, 90, and 135 Deg at a frequency of 1.125 MHz by division of the 4.5-MHz master clock frequency with bistable multivibrators. Applications of this scheme are described: (1) the proton-decoupled 13C spectrum of mesitylene; and (2) a 2-dimensional J spectrum of 13C in enriched MeI obtained in the F2 frequency dimension. [on SciFinder (R)]