Base Station Antenna Considerations - Vertex Standard VX-1700 Operating Manual

Base Station Antenna Considerations

As with mobile or maritime installations, antenna per-
formance is critical to base station communications sys-
tem effectiveness. Every effort must be made to ensure
that the impedance of the antenna system utilized with
the VX-1700 is as close as practicable to the specified
50-Ohm impedance value, and that mechanical and elec-
trical component integrity are maintained at all times.
For wide frequency range applications, Vertex Standard's
Model YA-30 Broadband Dipole Antenna may be ideal
for your communication requirements. Covering an oper-
ating frequency range of 1.6 -30 MHz, the YA-30 elimi-
nates the need for multiple antennas which might other-
wise be required for equivalent frequency coverage.
The type of antenna required for a particular communica-
tions distance will vary. A complete 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 ob-
structions 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, re-
member that the VX-1700 transceiver 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.
VX-1700
Install the ferrite core as
close to connector as
possible.
VX-1700 O
PERATING
B S
ASE TATION
M
ANUAL
I
I
NSTALLATION
Vertical antennas usually provide excellent coverage be-
yond 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
support 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 particular frequency.
For example, at 6 MHz a horizontal dipole 10 meters high
(33 feet) will provide excellent 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 dipole at a height of 10 meters could, ionospheric
propagation conditions permitting, be expected to provide
outstanding performance over the same 3000 km dis-
tance.
50° 60° 70° 80°
40°
30°
20°
10°
2.0 1.0
50° 60° 70° 80°
40°
30°
20°
10°
2.0 1.0
FC-40
NSTALLATION
90° 80° 70° 60° 50°
h=10m
40°
30°
20°
10°
0 1.0 2.0
90° 80° 70° 60° 50°
h=50m
40°
30°
20°
10°
0 1.0 2.0
Wrap the ends of the
waterproof cap with
sealing tape to protect
a g a i n s t m o i s t u r e
ingress.
Page 11