Informations on stations and frequencies are often insufficient, unreliable, outdated, simply wrong or all of this. We want to compile a list of really active stations. This direction is called the bearing and is expressed by the angle in respect of true North.
Radio waves contain both electric and electromagnetic fields.
A vertical antenna radiates a vertical electric field which produces a horizontal magnetic field. This is called a vertically polarized transmission. RDF utilizes the horizontal magnetic field. You get a maximum reading when the plane of the windings aims toward the transmitter and a minimum reading 90 degrees away from this. The latter is called a NULL position.