[en] Highlights: • Design of a 60–90 GHz chirped-pulse millimeter-wave spectrometer is described. • Sources of spurious frequencies in a broadband spectrometer are discussed. • The 1₀₁–0₀₀ rotational transitions of H¹⁵NO, HN¹⁸O, and D¹⁵NO are detected. • HNO pseudo-equilibrium $r_m^{(1)}$ geometry deduced from global analysis of isotopologues. An E-Band (60–90 GHz) chirped-pulse Fourier transform millimeter-wave spectrometer has been constructed for eventual kinetics and dynamics studies. The performance of the spectrometer is demonstrated with the molecule nitroxyl (HNO). Using the new spectrometer and by passing isotopically labelled methyl nitrite (CH₃ONO) through a pyrolysis nozzle, the spectra of minor isotopologues of HNO have been obtained. The observations on the isotopologues identified here, H¹⁵NO, HN¹⁸O, and D¹⁵NO, have been combined with the earlier isotopic observations, HNO and DNO, to create a global $r_m^{(1)}$ HNO geometry that approximates an equilibrium structure. The results are compared to high-level ab initio calculations.