User's Manual

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antenna will add to the excess path loss. Calculations of excess path loss should take this into
consideration using values approximately half those used for objects that obstruct the line of site
of the antenna. For a thorough understanding of this refer to ITU P526.
4.2.3 Fade Margin
A Fade Margin needs to be applied to link budget to take into account changes in the radio path
caused by changes in objects surrounding or in the propagating path. e.g. moving objects such
as traffic or the changes in foliage brought on by seasonal change. The fade margin used in the
calculation is a function of excess path loss. The fade margin requirement should be taken from
figure 9 using the excess path loss calculated above.
0 10 20 30 40
Excess Path Loss dB
- 12
- 10
- 8
- 6
- 4
Fade Margin dB
Fade Margin Required
Figure 9 Fade Margin vs Excess
Path Loss for 99.99% link availability
The use of MultiBeam Space-Time-Coding allows the OS-Gemini to achieve 99.99% availability
even in a totally obscured radio link operating with radio path fading up to 12 dB. This graph
should not be used for other products which may need nearly 40 dB fade margin for 30 dB excess
path loss
4.2.4 Maximum Path Loss
The Maximum Path Loss is the total path attenuation that the system can withstand and still
maintain 99.99% availability. Due to different spectrum licensing conditions in different regions
the Maximum Path Loss varies from county to country due to allowable output power differences.
In the USA this budget is 164 dB for BPSK and 150 dB for 16QAM.