These misunderstandings can cause real trouble for
the installer faced with decisions a knotty problem involving
signal interception. With respect to the common beliefs listed
here, concerning how many do you know the full truth?
IG: I have been working with antennas installation for
20 years and I agreed with the author. I have to add that in the
present times there are more myths then truth...
FICTION: The front to back ratio of an antenna is the ratio
between the sensitivity to a signal from a station in front of
the antenna and the sensitivity to a signal from a station to
the rear of the antenna.
FACT: This half-truth can be a damaging one if it is taken
literally. Strictly speaking, the front to back ratio is based
upon reception of a single signal originated from one point. The
antenna is first oriented so that it is picking up maximum signal
from this source while facing it. Then the antenna is rotated
through exactly a half turn- 180 degrees- and pickup of the same
signal is measured. The front- to- back ratio is the relationship
between these two readings.
Antenna patterns are such that
it is possible for a relatively small shift in orientation-say
a shift of 10 degrees- to produce a very great apparent change
in this ratio, often by as much as 5 to 20 times. These changes,
depending on the particular radiation pattern and the installation,
may be more important than an arbitrary ratio.