&gt; Is that a doubling of the radius or a doubling of the diameter<p>Those are equivalent: d=2r, so 2d=2(2r)<p>I very much doubt it means a doubling in the area or volume of the coverage region; seems far more likely that it means a doubling of distance.<p>But while this might only give twice the range with clear line of sight, lower frequencies tend to permeate obstructions better.