Vertex Standard VX-1400 Spezifikationen PDF herunterladen (Seite 18)

VX-1400 OPERATING MANUAL16

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

INSTALLATION

BASE STATION INSTALLATION

h=10m

90° 80°80° 60°60°

40°40°

30°30°

20°20°

10°10°

1.0 1.002.0 2.0

50°50° 70°70°

h=50m

90° 80°80° 60°60°

40°40°

30°30°

20°20°

10°10°

1.0 1.002.0 2.0

50°50° 70°70°

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