Measurements of plasma instabilities in the equatorial electrojet with HF and VHF radars have always been performed in a large scale turbulent medium. It is only in the exceptional case of a strong daytime counter-electrojet, as observed in Africa in 1977, that the background can be considered as almost laminar. Characteristics of the instability during such conditions are presented and appear to be completely different from those observed during electrojet conditions; especially the measured phase velocity varies with elevation angle and wavelength as predicted by the linear theory. The level of turbulence deduced from the measurement is found to be weaker than during usual conditions. Comparisons are made with theoretical works.