Afar AR24027, Руководство оператора

Страница: 73 / 100

AR24027 Operator’s Manual
6-8
6.4 Point-to-Point RF Path Analysis
A full point to point analysis should include:
•
Background noise evaluation of all locations where radios are to be installed
•
Determination of the minimum antenna height required to obtain “line-of-sight”.
•
Calculation of the expected Receive Signal Strength (RSS) level to be received at each of the
locations.
The background noise measurement is critical as it gives the operator a preview of the potential
performance variations and the feasibility of utilizing a particular radio at a location. For example, if
the background noise is found to be at the same level as the radio sensitivity (when set to maximum
speed), a tradeoff analysis can be conducted before installation to determine if lowering the data rate
will allow the radio sufficient link margin to operate. The
AR24027 includes a built-in spectrum
analysis tool that can be used to perform this background scan.
A line-of-sight is required to insure the best performance from the radio. The calculations below will
allow the operator to build towers and other mounting areas to the correct height before the antennas
are installed.
The calculation of the RSS level is useful for two purposes. The first is to determine the link margin
at the site. This information, when coupled with the background noise measurement, will tell the
operator if a link can be established and give a reasonable “a priori” estimate of the performance of
the system. In addition, the calculated RSS level allows the operator to do a quick check on the
integrity of the system installation by verifying that the actual RSS level (reported by the radio) is
close to the calculated value.
6.4.1 Antenna Height Analysis
Although the graph of Figure 6.2 provides a useful guide to antenna height requirements, a more
accurate determination of those requirements can be obtained by means of the analysis described in
the following steps. Note that computer programs, available from many vendors, can perform
portions of this procedure.
Requirements for this procedure are:
•
A topographical map of the installation site.
•
Graph paper, ten divisions per inch or equivalent metric scale
•
Straight edge
•
Calculator
Procedure:
1. On the topographic map, plot the precise location of each antenna site.
2. Draw a line between the sites; this line is the radio path.
3. On the graph paper, establish a vertical axis for elevation and a horizontal axis for distance. It is
usually easiest to make the vertical axis in feet or meters and the horizontal axis in miles or
kilometers.