  We present a study of the radio continuum properties of two
luminous/ultraluminous infrared galaxy samples: the OH megamaser (OHM) sample
(74 objects) and the control sample (128 objects) without detected maser
emission. We carried out pilot observations for 140 objects with the radio
telescope RATAN-600 at 1.2, 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2019-2021. The
OHM sample has two times more flat-spectrum sources (32 per cent) than the
control sample. Steep radio spectra prevail in both samples. The median
spectral index at 4.7 GHz $\alpha_{4.7}=-0.59$ for the OHM sample, and
$\alpha_{4.7}=-0.71$ for the non-OHM galaxies. We confirm a tight correlation
of the far-infrared (FIR) and radio luminosities for the OHM sample. We found
correlations between isotropic OH line luminosity $L_{OH}$ and the spectral
index $\alpha_{4.7}$ ($\rho$=0.26, p-val.=0.04) and between $L_{OH}$ and radio
luminosity $P_{1.4}$ ($\rho$=0.35, p-val.=0.005). Reviewing subsamples of
masers powered by active galactic nuclei (AGNs) and star formation revealed
insignificant differences for their FIR and radio properties. Nonetheless,
AGN-powered galaxies exhibit larger scatter in a range of parameters and their
standard deviations. The similarities in the radio and FIR properties in the
two samples are presumably caused by the presence of a significant amount of
AGN sources in both samples (47 and 30 per cent in the OHM and control samples)
and/or possibly by the presence of undetected OH emission sources in the
control sample.
