We present the first results of our program of spectroscopic observations with orbital phase resolution of short-period active binaries. We have collected simultaneous data in the lines Hα, Hβ, and the infrared triplet (IRT) of Ca II (8498 and 8542 A). In this paper we discuss the methods used to analyze the spectra and describe the results obtained for the systems CG Cyg, BR Vir, and ER Vul. All the stellar components of the two binaries present emission in the lines analyzed, with phase dependent variations. The Hα and Hβ lines show well correlated changes, while the Ca II (IRT) lines display a different behavior with respect the Balmer lines, suggesting that they were formed in different regions. In CG Cyg, BR Vir, and ER Vul the measured ratios are: EHα/EHβ ˜&=1-3 and E(8498 Å)/E(8542 Å) ˜=1-3, both values being indicative of optically thick formation. These ratios of the systems that we have studied, conformed by main sequence stars, are significantly lower than the values reported in the literature for long-period RS CVn systems with subgiant components.