The use of interference signal cancellation has been around for
some time. The idea is to use an auxiliary antenna (almost any
random length of wire) in addition to the main receiving
antenna. As the two antennas are physically spaced from each
other and also unlikely to have similar field patterns, the
amplitude and phase difference between the two antennas for an
interfering signal can be expected to be different to that for
the desired signal. This particularly applies to a localised
interference source where that source is largely coupled into
the antenna by induction. This induction field follows a
different law of signal attenuation verses distance to that of
the radiation field by which the distant desired signal is being
received. The two antenna outputs are combined after modifying
their relative signal levels and phase such that the
interference signal from one antenna is equal but opposite in
phase to that from the other antenna. The interference signal is
cancelled but as the two desired signals h