  Several binary systems consisting of a massive star and a compact object have
been detected above 100 GeV in the Galaxy. In most of these sources, gamma-rays
show a modulation associated to the orbital motion, which means that the
emitter should not be too far from the bright primary star. This implies that
gamma-ray absorption will be non negligible, and large amounts of secondary
electron-positron pairs will be created in the stellar surroundings. In this
work, we show that the radio emission from these pairs should be accounted for
when interpreting the radio spectrum, variability, and morphology found in
gamma-ray binaries. Relevant features of the secondary radio emission are the
relatively hard spectrum, the orbital motion of the radio peak center, and the
extended radio structure following a spiral-like trajectory. The impact of the
stellar wind free-free absorption should not be neglected.
