Installing the antenna
12 Automatic Tuning Whip Antenna 9350 Installation Handbook
The installed antenna should enable easy access to the
connectors.
Earthing
Most mobile antennas are considerably shorter than a quarter
wavelength at HF, and can exhibit an extremely low radiation
resistance. Consequently, their efficiency is reduced compared
with the quarter-wave radiator that they represent. This can be
improved by good installation practices, and most importantly,
by the provision of a low-impedance earth return for the
antenna.
Due to the relatively poor earth plane surrounding a mobile
HF antenna, best use should be made of what is available. A
reduction in any losses can increase antenna current and
radiation. This can often be achieved by providing a good
earth connection from the base of the antenna to nearby
bodywork. An earth strap is provided for this. Connections to
the vehicle chassis are not as effective because many 4WD
vehicles have insulating mountings from body to chassis.
A strong metal plate that is large enough to support the
antenna will provide efficient earthing. The plate should be
welded to the chassis or some other part of the vehicle’s frame.
The mounting bracket and plate must be free of rust and paint
to allow metal-to-metal contact between the base of the
antenna and the mounting bracket. This electrical bond is the
basis for effective RF earthing. RF currents flow on the
conductor surface, therefore good RF earthing requires
conductors with large surface areas.
NOTE
The shroud over the antenna tuner can flex up to
150 mm (6 in) without damage to the shroud.
NOTE
Conductive grease should be used on the
touching surfaces to help prevent corrosion.
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