Mandelstam's early works in radio-engineering are described. The author takes into consideration not only Mandelstam's publications but also his patents and his private communications. It is emphasized by the author that Mandelstam reverted to his Strasbourg ideas in his Moscow lectures on oscillations. Mandelstam's polemics with the English radio-physicist J.A. Fleming are described and an attempt to reconstruct a political background of these polemics is made.