A second fixed-frequency RF source is introduced within the technique of Raman heterodyne detection of nuclear magnetic resonance and used to burn spectral holes in the I2=+or-1/2 implies/implied by +or-3/2 transitions of Eu3+ in KEu(WO4)2. At 1.8 K the hole has a width (FWHM) of 350 Hz whereas the homogeneous width of the transition determined from Raman heterodyne-detected nuclear spin echoes is 220 Hz. At 4.2 K the width of the RF hole is 1300 Hz and the homogeneous width is 660 Hz. The holes are asymmetric in shape and displaced by about 100 Hz to the low-energy side of the burn frequency; this is attributed to cross-relaxation between the resonant ions and ions with adjacent resonant frequencies. The effect of the burn frequency and burn power on the shape and depth of the holes is reported. In a magnetic field, burning in one Zeeman component also gives auxiliary holes in the other Zeeman components. The hole spectrum gives an increase in resolution of an order of magnitude compared with the regular Raman heterodyne scheme. © 1987 IOP Publishing Ltd.