Page 37
Before placing your HW-30 into operation a
able. Refer to the back of Pictorial 2 for a
review of the control functions would be advis-
complete explanation of all controls.
TYPES OF ANTENNAS
Various types of antenna designs exist which
differ in complexity, directional characteristics,
polarization and cost. The simplest of the hori-
zontally polarized type is shown in Figure 11,
and is generally referred to as a "dipole" or
"doublet." Its directional characteristics are not
very pronounced and represent an approximate
"figure eight" pattern. The antenna as shown is
properly fed with 75 a ribbon line (special twin
lead), although doublets are frequently fed with
75 n coax with good results.
Simple, practical antennas for vertical polariza-
tion are the "ground plane" and "coaxial" types,
either of which is essentially omni-directional,
that is, they radiate equally well in all directions
in the horizontal plane.
The choice of polarization is largely a sectional
one. Some areas are predominately horizontal
where others are vertical and it is suggested
you use the polarization generally in use in your
area. Beam antennas will provide typical ef-
fective radiated power gains up to 50 or 60,
depending upon the number of parasitic elements
used.
This means in effect that both transmitted and
received signals will be up to 50 to 60 times
EACH ELEMENT
APPROXIMATELY 19f
..%
GROUND PLANE
) --
ANTENNA
\AL
TYPE
I
Figure 11
stronger in signal strength (in the direction of
maximum radiation) than when a simple doublet
is used.
In viewing Figure 12, it is apparent that some
means of turning the antenna is required unless
point-to-point communication is the only re-
quirement. Most any of the inexpensive televi-
sion antenna rotors are adequate for a single
bay beam of reasonable length on 2 -meters.
The choice of a directional antenna
versus an
omni-directional one is largely dependent upon
application. Where strong signals are consist-
ently present or where it is undesirable to have
to rotate the antenna, the simpler types of an-
tennas lend themselves readily. The highly di-
rectional arrays find good application in weak
signal communications, point-to-point commu-
nications, or where it
is desirable to reject
signals from other interfering stations by ro-
tating the antenna.
There are numerous other antenna systems
available for these frequencies. Among many
others,
excellent references on the subject
appear in VHF HANDBOOK by Orr and Johnson;
THE RADIO AMATEUR'S HANDBOOKpublished
by The American Radio Relay League or the
more popular monthly periodicals.
DOUBLET OR
DIPOLE
ANTENNA
YAGI OR
BEAM
ANTENNA
DRIVEN
ELEMENT
Figure 12
To Next Page
Loading...
