Display Characteristics; Multi-Path Interference - Cal Amp Dataradio HiPR-900 User Manual

7.2.1 Display Characteristics

There are two main visual characteristics to the display (see Figure 85):
1. The noise floor –
Indicates how much RF interference is present. Other system(s) with different System ID's, and
any other signals in this shared band, can and will increase the noise floor and could necessitate a
stronger signal to achieve desired system throughput. A rough noise floor that changes every few
seconds likely indicates that other hopping or spreading signals are present in the band.
2. System's Received Signal Strength –
Ideally, the system's signal strength should be at least 20dB above the floor noise (more is al-
ways better). Smooth but irregular RSSI level variations across the RF band (see Figure 86 be-
low) relate to how much multi-path signals are interfering with reception at this location. A flat
level indicates a better signal path than an uneven level.

7.2.2 Multi-path Interference

Achieving RF band flatness from an antenna system is a function of the type and quality of antenna used
and how well a direct line-of-sight transmission path is realized. Try using directional antenna to reduce
multi-path reflections, aiming away from noise sources by changing antenna directions slightly, by chang-
ing antenna polarization, changing the dual antennas position relative to each other or changing their loca-
tion.
Note:
As stated in section 2.2.3, minimum separation for a diversity reception is 5/8 wavelength (ap-
proximately 8 inches – 21cm) for fixed applications.
The overall throughput can be measured after a change is made (do not forget to clear the statistics before
a new measurement is taken) and a correlation to the spectrum made visually.
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Figure 86 - Representative Multi-path City Spectrum Example
79 HiPR-900 User Manual