Experimental source separation in the H.F. band (3-30 MHz) : comparison between a blind and a parametric method

A compact system of direction finding has been developed for the past three years which operates on a set of seven collocated H.F. active antennas. It has been shown that the estimation of the direction of arrival can be efficient as the diversity of their spatial responses replaces the space diversity of a classical array. That technique implies however a particular computation of the Music algorithm, noting that such an array is heterogeneous. A significant number of experiments, which involved broadcast transmitters more than 700 kms far from the receiving site, validated this concept. Further on, a source separation of the H.F. multipaths is investigated, aiming to reduce the amplitude fading and to improve the bit error rate in a digital transmission. The paper proposes a comparison of two possible techniques: a classical spatial filtering (least mean squares filter) or a blind algorithm resorting to second order statistics