The interaction of circularly-polarized Alf¿n waves with the surrounding plasma in high speed solar wind streams is investigated. Alfv¿n wave modulational instability is discussed and nonlinear envelope soliton solutions of the magnetohydrodynamics equations are introduced. The characteristics of these Alfv¿n solitons are compared with observational results obtained from Helios I and II. A model of the expected turbulent spectrum due to a collection of such solitons is constructed and its radial dependence is investigated, again along with comparison to Helios data.