Exalt Communications, Inc.
EX-5i Installation & Management
5000005
27
2006-05-17
In some cases, the choice of transmission line will not be coaxial cable, but instead will be air-
dielectric waveguide. This is an expensive solution and is generally not necessary, but may be
required for very long transmission line runs and/or for very long link distances and/or for
systems that require extremely high reliability.
The following is a representative sample of transmission line types that are recommended for this
radio:
•
Andrew HELIAX
®
LDF4-50, 1/2-inch solid copper shielded coaxial cable, 6dB/100ft.
•
Andrew HELIAX
®
LDF4.5-50, 5/8-inch solid copper shielded coaxial cable, 4.7dB/100ft.
•
Times LMR-600, 1/2-inch braided coaxial cable, 7.3dB/100ft.
•
Times LMR-900, 5/8-inch braided coaxial cable, 4.9dB/100ft.
There are several other brands and models of transmission line that are perfectly acceptable. As
mentioned, for extremely long transmission lines and/or extremely long radio paths, it may be
necessary to use waveguide transmission line instead of coaxial transmission line. In these cases,
waveguide type EW52 is recommended, with a loss of 1.3dB/100ft.
It is critical that the transmission line and antenna be capable of supporting the same type of
connector, or easily adapted. Keep in mind that it can be important to minimize the number of
connectors and adaptors, so it is ideal if they match directly without adaptation. In most cases,
transmission line will allow for N-type male connectors and antennas have N-type female
connectors. For waveguide, the waveguide flange can typically accommodate a direct adapter to
an N connector, or alternatively, the antenna can be purchased with a direct waveguide
connection. But often a flexible coaxial jumper is needed to connect between the waveguide to
the antenna, as waveguide is generally inflexible and can be mechanically challenging to align to
the exact antenna connector location.
If possible, connect the primary transmission line directly to the antenna. It is desired to have the
fewest possible pieces of transmission line in the system, to minimize losses and points of failure
from connectors, and the antenna can typically accommodate a direct connection if planned in
advance. You may use a 90-degree adaptor for the connection to the antenna, if necessary – but
be certain to confirm that all connectors and transmission lines are properly specified for the
operating frequency (5250 to 5850 MHz, in this case) with minimum loss, proper impedance (50
ohm) and proper Voltage Standing Wave Ratio (VSWR) characteristics.
Transmission line connector termination is perhaps the most critical element of the installation.
Many ‘factory built’ RF transmission lines may actually not provide the proper characteristics
for proper transmission, despite their published specifications, often due to the fully- or semi-
automated process of factory termination, which may not have considered the frequency of your
system. When buying pre-terminated transmission line, it is strongly advised to receive
documentation of the test measurements on the connected transmission line showing that the loss
characteristics and VSWR are within specified limits specifically at your operating frequency. In
addition to factory-built transmission line, self-terminated transmission line can suffer the same
issues. Always follow the manufacturer’s termination process EXACTLY, and only use the
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