SECTION 3. RADIOTELEMETRY NETWORK COMPONENTS
3-6
3.3.2 ANTENNA ORIENTATION
Antennas must be oriented correctly to allow
communication between RF sites. First
determine if your antenna is omnidirectional or
unidirectional.
An omnidirectional antenna will transmit/
receive in a full 360 degree circle. Generally, an
omnidirectional antenna will be a straight
cylindrical rod which is to be mounted vertically
at the top of a tripod.
A unidirectional antenna is designed to
transmit/receive in a particular direction, or in a
specified sector. There are various shapes of
unidirectional antennas. The most common is
the Yagi antenna (see Figure 1-2). The
elements of a Yagi antenna can be mounted
either vertically or horizontally, corresponding to
either vertical or horizontal polarization.
Normally, all antennas will be mounted with
vertical polarization. Whichever polarization is
used, be sure to keep antennas at all sites
identically polarized.
3.3.3 ANTENNA CABLES AND CONNECTORS
The most common cable type to connect a
radio to the antenna is a coaxial RG-8A/U
cable. Two connectors are required for each
length of cable. The connector for the radio is a
BNC type connector. The connector for the
antenna is usually either a Type-NM or Type-
NF. The BNC, Type-NM, and Type-NF
connectors are shown in Figure 3-6. The Type-
NM (male) connector is for antennas with a
female receptacle, and Type-NF (female) for
antennas with male receptacles.
A Campbell Scientific antenna cable complete
with connectors is specified as either COAX
NM-L or COAX NF-L. COAX NF-L is a coaxial
RG-8A/U cable with a BNC connector on one
end and a Type-NF connector on the other.
See Table 3-7 for cable requirements for
common antennas.
Due to power loss through the cable, the length
of coax cable cannot be extended to any
desired length. The amount of power loss is
dependent on the radio frequency. RG-8A/U will
lose approximately 3.1 dB/100 ft. at 200 MHz
and 5.0 dB/100 ft. at 400 MHz. Power loss
calculations are reviewed in Appendix C.
FIGURE 3-4. The PD237 Crossover Plate
Antenna Mount
FIGURE 3-5. The PD46 Clamp Mount
FIGURE 3-6. Type-NM (male), BNC, and
Type-NF (female) Connectors
