> You need to place the first insulator as close to the
> tower as possible to prevent coupling to continuous
> wire from one insulator, through the tower, to another
> insulator.
That is not necessarily where the problem is. The guy wire can be
resonant with the electrical length of the tower at the attachment
point, and not even involve another guy wire. When you attach a
guyline directly to the tower, you bring the entire tower into
play...like a sloper does.
Also, conductors do not need to be resonant to re-radiate or to
affect pattern. Any RF current flowing in a conductor will cause the
conductor to radiate. The amount of radiation is related to the
amount of current and the distance over which that current is
flowing, the "ampere/feet". Long guy wire sections can have a bad
effect even when not resonant.
To have an unwanted effect, a conductor simply needs to have
enough induced current to develop a field that affects nulls of the
antenna. The longer the wire the less current it needs for the same
radiation. If a guy line re-radiates a field that is 15 or 20 dB less
than the main lobe of the antenna, it can still noticeably reduce the
depth of antenna nulls!
The best rule is to avoid resonant lengths AND keep the lengths in
strong field areas of the antenna much shorter than 1/2 wl. This
would include if you point other antennas through the guylines from
some distance away. Near the antenna, guy lines should not
electrically connect to the tower.
73, Tom W8JI
W8JI@contesting.com
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