A new separated local field NMR experiment, designed for accurate measurements of heteronuclear dipolar couplings, is described. The pulse sequence is based on a homonuclear decoupling windowless heteronuclear isotropic mixing approach to achieve the coherent polarization exchange between the z-components of the magnetizations in heteronuclear spin system. This technique suppresses chemical shifts and frequency offset variations irrespective of the dipolar coupling value. The experiment is demonstrated on a columnar liquid crystal.