Nulls in radiation pattern

[kq6qv]

Nulls in the radiation pattern can be useful. If you rotate the antenna so that a null points toward an interfering signal, that signal is eliminated. Some interference situations that might benefit from this trick include:
> Adjacent channel interference (a very strong station one channel up or down)
> Co-channel interference (two weak stations on the same channel)
> Multi-path interference (usually caused by the direct path being blocked)
> A very close transmitter (a neighborhood FM station, police station, taxi company, etc.)
> An industrial noise source (a factory, a clinic, a malfunctioning power transformer)

For example, the Channel Master 4228 has nulls on both sides at 30 and 90 degrees:
[img]http://www.hdtvprimer.com/ANTENNAS/cm4228az.gif[/img]
Yagi/Corner-reflector antennas have no nulls. LPDA antennas have nulls at 90 degrees, but LPVA antennas have no nulls. To make rabbit ears have nulls (at 90 degrees) lower them into a straight dipole. See also