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Recreational Vehicles and especially Motor Homes having much greater surface area will therefore
provide a more extensive and effective ground system than a large number of radial wires
occupying the same space as the Motor Home or Recreational Vehicle.
As in mobile installations, a vertical antenna may be mounted almost anywhere on the body of the
vehicle or Motor Home and made to operate with reasonably low VSWR, but it is generally
considered that the best possible location for a mobile antenna is in the middle of the roof of the
vehicle, i.e., at the center of the vehicle's ground plane and at a point where the antenna will not be
in the "shadow" of any part of the vehicle. It is not usually convenient, or even practical to install a
relatively tall vertical on the roof of an Recreational Vehicle or Motor Home for any number of
reasons, so the next best procedure would be to install a vertical antenna with its base at the same
level as the roof, preferably near the middle of one of the longer sides. The exact way in which this
may be done is a matter of convenience, but a short mast extending from ground level to the roof of
the Motor Home and Recreational Vehicle and placed alongside the building or Recreational
Vehicle would provide a stable and sturdy support with a minimum of mounting brackets and other
modifications to the Recreational Vehicle or Motor Home. For portable operation such a mast could
simply be lashed alongside the Recreational Vehicle with the base in a shallow hole in the ground
for additional support, and there would be no harm in extending the mast a few inches above the
roof level to permit attachment of ropes which could be used to hold the mast firmly against the side
of the vehicle and to prevent side sway.
This system has been used successfully with various types of Recreational Vehicles, travel trailers
and even passenger automobiles during portable operation. For "L" shaped mobile homes a vertical
antenna should be placed in the corner of the "L" so that the metal roof will provide ground plane
coverage over 270 degrees.
In all cases the base of the vertical antenna should not be more than a
few inches away from the Motor Home or Recreational Vehicle so that
the shortest possible lead may be run from the ground connection of the
antenna to the metal body, as the length of this ground lead will
effectively lengthen the antenna itself on all bands, and detuning can
occur in some cases. A good electrical connection between the body of
the Recreational Vehicle or Motor Home and the antenna is important,
and in the case of mobile homes it would be a good idea to make sure
that good electrical contact exists between the different parts of the
metal body. Discontinuities can often lead to the production of
harmonic radiation and TVI.
The essential circuit connections are shown in the diagram above. For
permanent installations the bottom of the mast may be set deeper in the
ground, and concrete may be used for greater strength and stability. The
upper portion of the mast should be securely attached to the side of the
building. Steel TV mast sections are readily available in lengths of ten
feet and the mounting posts of Butternut
®
HF verticals will slide into
those which have an outside diameter of 1-1/4 inches and a wall
thickness of .058 inches. Other vertical antennas may use different
mounting techniques and requirements, so be sure to select a mast that
will be suited to the particular situation. The main point to keep in mind is that the mast should not
extend more than a few inches above the level of the roof so that the ground lead may be kept short.
