All this discussion about RDF overlooks the issue of polarization. If you make an array of verticals with a certain RDF (assuming noise comes from all directions uniformly), the array will be better than an individual vertical by the RDF factor. However, what I have found is that a horizontally polarized antenna, such as a low dipole frequently receives considerably better than a vertical. In that case, you would be better off using an array of low dipoles. The reason why horizontal polarization can be better is that the horizontal component of terrestrial based noise is highly attenuated over distance as a ground wave.
Rick N6RK _________________ Topband Reflector Archives - http://www.contesting.com/_topband