A computer‐controlled pulsed electron spin resonance spectrometer operating atS‐band (2–4 GHz) is described. The instrument is designed for the study of weak interactions between paramagnetic centers and surrounding magnetic nuclei by electron spin‐echo modulation techniques. The incorporation of loop‐gap resonators gives good sensitivity and allows use over the full octave bandwidth range. Free‐induction decay and electron spin‐echo signals at room temperature and at liquid‐helium temperature are shown in selected sample types. The expected increase of the electron spin‐echo modulation depths relative toXband (∼9 GHz) frequencies is demonstrated for proton modulation.