RXTE Observations of the Microquasar GRS 1915+105

We analyse a set of three RXTE Target of Opportunity observations of the Galactic microquasar GRS 1915+105, observed in April 2000. We concentrate on the timing properties of the source, and examine the properties of a low frequency QPO, with its harmonic, in several energy ranges. The source was found in two different states of the spectro/temporal classification of Belloni et al. (2000), and exhibited in the three observations a strong, low frequency QPO together with a strong harmonic. We discuss the properties of the QPO, of its harmonic and of their spectral behaviour in the framework of the Accretion Ejection Instability (AEI) (Tagger & Pellat, 1999; Varni\`ere, Rodriguez & Tagger, 2001; Rodriguez et al., 2001).