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If RADAR presents a problem for Iridium Pilot Land Station it will most likely be an out of band type
interference. Given the RADAR antenna spends most of the time facing away from the ODU the noise floor
may display a cyclic pattern of raised and normal amplitude causing something like every third channel to be
elevated. Since the scan rate of the SST and the sweep rate of the RADAR are not synchronous the affected
channels may "walk" across the display from sweep to sweep causing the noise floor of a long duration scan
(> 10 scans) to elevate nearly uniformly.
Peak values of normal Iridium signals are typically -90dBm or below. Peaks in excess of -85 dBm should be
suspected as terrestrial interferers and be tracked down.
At the conclusion of the survey the user should stop the tool and then select the file menu button and save the
file using the default naming convention which contains the IMEI of the unit under test along with a time date
stamp. The data is stored as a comma separated value (CSV) and can be sent to a tier 2 or tier 3 organization
for further assistance in analysis. Tier 1 is end user support from the (SP) service provider. Tier 2 is SP support from
Iridium. Tier 3 is engineering support to Tier 2.
The tool has additional configuration parameters to allow the user to scan smaller portions of the band using
the slider just below the command bar. This can be useful in focusing the display on say 10 channels of interest
around a suspected interferer and collecting multiple short scans in 1/25th the time of a fill scan as shown in
Figure 31.
Figure 31.
Examples of "Bad" Site Survey Plots
The following three examples simulate interference of the ODU receiver and are examples of bad installation
locations. Figure 32 shows interference from a high power HF radio near the ODU. The transmitter was keyed
for part of a 90 second scan (starting at ch 177 and ending on the subsequent scan at ch 88) and shows the
current mean noise floor rising above the -120 dBm limit across the band (broadband noise). Additionally
antenna 7 can be seen to 20 to 30 dB of excess noise meaning high elevation passes would be blocked.
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Iridium Pilot Land Station Installation Guide
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