Trango Broadband Wireless Access5830™ User Manual
User Manual Rev 1
35
percentage of time the link is available versus total outage time per year
(source: FCC OET Bulletin 70).
AVAILBILITY
OUTAGE TIME PER YEAR
99.9%
9 hours
99.99%
1 hour
99.999%
5 minutes
99.9999%
30 seconds
Availability is largely based upon the fade margin allowance specified versus
the signal fading due to multipath, foliage, and weather effects. The fade
margin must be greater than all signal fading losses for the link to be
“available”.
If the fading losses are greater than the fade margin the link is considered to
be “unavailable”, although a gradual degradation of the link quality will
generally occur instead of the link being completely disabled.
For LOS links, availability is based mainly upon weather effects.
If the fade margin is greater than these losses, a link will be available during
these rain events assuming no other impairments to the link have occurred such
as misaligned antenna, etc.
The M5830S-SU-EXT with 31 dBi dish is designed to operate with a maximum
radius of 20 miles using a fade margin of 12 dB, so it would still operate with
no degradation during the example events discussed in 3.4.2.4 above.
In the continental United States, the southeastern part of the country is
subject to an average of 5.26 minutes per year where the rain rate exceeds 150
mm/hr. If we assume that the fading losses will be greater than 12 dB during
this time, the M5830S link will be “unavailable” for that time unless the fade
margin is increased. This corresponds to an availability of 99.999%.
6.7.
Site Survey
After choosing the appropriate fading margin allowance and AP configuration,
it is important to conduct a site survey. Both the AP and SU units have several
commands to allow measurement of the RF spectrum and assist in the selection
of channels for best operation. The basic procedure is as follows:
Install an AP in the desired location, aligned towards the desired coverage
area.