Vertex Standard VX-1400, Руководство по эксплуатации

Страница: 18 / 56

VX-1400 O
PERATING
M
ANUAL
16
Base Station Antenna Considerations
As with mobile or maritime installations, antenna performance is critical to base station
communications system effectiveness. Every effort must be made to ensure that the im-
pedance of the antenna system utilized with the
VX-1400
is as close as practicable to the
specified 50-Ohm impedance value, and that mechanical and electrical component integ-
rity are maintained at all times.
For wide frequency range applications, Vertex Standard’s Model
YA-30
Broadband Di-
pole Antenna may be ideal for your communication requirements. Covering an operating
frequency range of 1.6-30 MHz, the
YA-30
eliminates the need for multiple antennas
which might otherwise be required for equivalent frequency coverage.
The type of antenna required for a particular communications distance will vary. A com-
plete discussion of this topic is beyond the range of this manual; however, a few general
guidelines will be offered herewith.
Any antenna to be installed should be free of nearby obstructions which might interfere
with its radiation pattern. The antenna, its support structure, and its cables must never be
installed in such a manner that would allow them to contact with power or telephone lines
in the event of a catastrophic windstorm or other cause of major failure. An adequate
safety is usually provided by keeping the antenna and its support structure 1.5 times the
height of the support plus the length of any antenna or guy wires attached to the support.
When installing a balanced antenna such as a dipole, remember that the
VX-1400
trans-
ceiver is designed for use with an (unbalanced) coaxial feedline. Always use a balun or
other balancing device so as to ensure proper antenna system performance.
Vertical antennas usually provide excellent coverage beyond about 1000 km (600 miles),
but very poor coverage at closer distances. Horizontal antennas are frequently better for
shorter distances, but they may require a stout sup-
port structure such as a tower. The height of the hori-
zontal antenna, and the nature of the ground below it,
have a profound impact on the favored launch angle
for the main radiation lobe from the antenna at a par-
ticular frequency. For example, at 6 MHz a horizon-
tal dipole 10 meters high (33 feet) will provide excel-
lent local coverage out to about 500 km (300 miles);
however, at the same frequency the dipole would have
to be much higher (perhaps 50 meters or 165 feet) for
satisfactory communication over a range of 3000 km
(1800 miles). On the other hand, at 26 MHz the same
I
NSTALLATION
B
ASE
S
TATION
I
NSTALLATION
h=10m
90° 80° 80° 60° 60°
40° 40°
30° 30°
20° 20°
10° 10°
1.0 1.0 0 2.0 2.0
50° 50° 70° 70°
h=50m
90° 80° 80° 60° 60°
40° 40°
30° 30°
20° 20°
10° 10°
1.0 1.0 0 2.0 2.0
50° 50° 70° 70°