Page 39
1/4 WAVE LE
,NGTH
Figure 14
3/4 WAVE LENGTH
INSTALLATION
Various factors should be considered before
your HW-30 is installed at a fixed location.
Several of these factors
are
listed below.
The polarization of the antenna system (the
relative direction of the radiating elements) is
quite important at the VHF frequencies. The
majority of amateurs on 2 -meter have hori-
zontally polarized antennas; that is, the radiating
element or elements are parallel to the surface
of the earth. It should be pointed out that, even
at short ranges it is usually difficult to com-
municate between two stations, if one is hori-
zontally polarized and the other polarized verti-
cally.
Most horizontally polarized antennas
show directional properties; that is, they will
transmit and receive a stronger signal in one
or more directions than in others. It is sug-
gested that you use the polarization in general
use in your area.
Non -directional, vertically polarized antennas
frequently find application in fixed -to -mobile
unit operation where the mobile units location is
not predictable.
Try to locate your HW-30 near a good earth
ground, such as a water pipe going directly
underground. Although the use of an earth ground
is not essential for proper operation of
your
HW-30, in many instances greatly improved
operation will result, and it is considered good
practice to have the system grounded.
INSTALLATION AT A MOBILE LOCATION
The section to follow will deal specifically with
installation in an automobile or light truck, but
the majority of this information is also applicable
to other mobile installations (boats, etc.). See
Figures 14 and 15.
Figure 15
INFORMATION
In a mobile installation, the antenna system is
of great importance. Any mobile system is at
a
decided disadvantage, due to the lack of a good
earth ground, the only ground being the capacitive
coupling between the vehicle body and the earth
below.
With few exceptions, the antenna best suited for
mobile service will be either some sort of
vertically polarized whip antenna (Figure 14) or
the current "halo" antenna for horizontalpolar-
ization. It is suggested that you contact hams in
your area to determine the type of polarization
used in your locality since some areas prefer one
over the other and it becomes very difficult to
maintain communication under cross -polar-
ization conditions at this frequency. For vertical
polarization, a 1/4 wave (approximately 19") or
3/4 wave (approximately 57") whip,
suitably
placed, as shown in Figure 14, is generally the
most practical. These antennas use the metal
vehicle body as their "ground plane" and for
this reason are normally somewhat directional
when installed in a more practical location, such
as the rear of the vehicle. If installed in the
roof
center, radiation is usually better and
very little directional properties will be noted.
No specific information about the actual direc-
tional characteristics of any given installation
can be given here due to variables in antenna
location, but a typical installation might be ex-
pected to yield a radiation pattern similar to
that shown in Figure 15.
This directional characteristic normally causes
no serious difficulty, but you should be aware of
its existence.
In nearly all mobile installations, the ambient
noise level will be higher than at a fixed location.
For this reason, serious consideration should
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