Origin of Echo-Enabled Harmonic Generation

In this paper I present overview of two preprints that were published at Budker Institute of Nuclear Physics in 1980 [1,2]. These original publications describing harmonic generation technique which has the same foundation as Echo-Enabled Har-monic Generation (EEHG). They recently become available online [3], but they are still unknown to FEL community. This paper is an attempt to cur-rent this omission.