Campbell Scientific RF320-Series Ritron VHF/UHF Radios - Manual (Page 22)

RF320-Series Ritron VHF/UHF Radios
the received signal strength. There exists an area about the centerline of an
EM-wave propagation path that must be clear of obstructions. This area is
termed the Fresnel zone (pronounced fray-nel) and the property that must be
determined for a path of propagation is the Fresnel zone clearance. The Fresnel
zone may be loosely imagined as an elliptical balloon stretched between the
transmit and receive antennas with the maximum radius located at a distance
midway along the path. Technically, the Fresnel zone comprises a theoretically
infinite number of concentric zones about the centerline, but it is the first or
outermost zone that we are concerned with. As with link budget, a web search
for “Fresnel zone” will reveal a number of on-line calculators for determining
the Fresnel zone radius at a given distance, frequency, and antenna elevation.
While a Fresnel zone radius can be readily calculated, the difficult aspect of
this effort is in determining what obstructions may lie within the path. This is
especially true for paths over irregular terrain and great distances. For this, a
path survey (also known as a path analysis) will be required. A path survey will
map the path over a terrain profile generated from a topographical database.
Some surveys may include a depiction of the Fresnel zone so that potential
obstructions are easily identified. If a significant obstruction is identified,
increasing the antenna elevation at one or both ends of the link may provide the
needed clearance.
There are a number of software packages that can be utilized for a path survey,
but bear in mind that man-made obstructions may not be identified. These tools
should be used for planning purposes only.
8. Troubleshooting/Maintenance
8.1 Maintenance
The RF320-series radios require no maintenance in terms of periodic service
adjustments or alignment. However, it is recommended that a visual inspection
of the radio and its constituent components, including RF cables and antenna,
be performed routinely. Inspect the system for damaged or loose components
or connectors; chaffing of cables and conductors; and any evidence of moisture
or corrosion.
Additionally, it is recommended that the functional checks listed in Section 8.3,
Radio Functional Checks, be performed periodically and a record of the results
be maintained. A review of these records could illuminate signs of performance
degradation, and allow for corrective action to be taken before a loss of system
functionality occurs.
8.1.1 Basic Test Equipment
For maintenance and troubleshooting purposes, it is strongly recommended that
a basic collection of tools and diagnostic equipment be procured and
maintained. An adequate collection of basic test equipment would include a
digital multimeter, RF power meter, antenna analyzer or SWR meter, and an
RF channel-scanner. The following list is provided only as representative
example of suitable equipment. Campbell Scientific implies no official
endorsement of the specific equipment or manufacturers.
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