Comtech EF Data MDX420 SkyWire Manual - Manual (Page 69)

MDX420 SkyWire™ Satellite Network Gateway SkyWire Controller (GUI)
MN-MDX420 Revision 6 7–13
3) Set a Max TX Power Level (dBm) (any figure from 0 to -25). Note: Do NOT set an
excessively large Max TX Power level unless there is a reason to believe all of the
excess power could actually be used strictly for uplink rain fade.
4) Enable AUPC by checking the box
5) Click Apply
TX % Fade: The demodulator carrier level used in AUPC is a measurement of it’s own burst as
seen by the demod from the satellite. Unfortunately if there is a fade condition at the site, what
the demod is seeing is both the uplink fade and the downlink fade. We want to compensate for
the uplink fade only for reasons mentioned above, so we need to determine what percentage of
the fade is due to the uplink and what percentage of the fade is due to the downlink. Generally
speaking uplink frequencies are higher than downlink frequencies and because of this there is
generally more fade on the uplink (this is a good thing because this is what we can compensate
for). The TX fade percentage can be calculated using the following math:
TX% Fade = TX Fade /(TX Fade + RX Fade)
Example: Ku Band link with with 4.4dB of total fade. Due to the frequencies used, 2.4 dB is due
to the uplink and 2.0dB is due to the downlink. This site has a TX% Fade of 55%.
Below is a table of common TX Fade % Figures using the center of each Band as the metric for
fade %
Downlink (GHz) Uplink (GHz) TX Fade %
Band f
low
f
high
f
mid
f
low
f
high
f
mid
TX Fade / (TX + RX Fade)
C-band 3.4 4.2 3.8 5.85 6.65 6.25 72%
X-band 7.25 7.75 7.5 7.9 8.4 8.15 54%
Ku-band 11.7 12.2 11.95 14 14.5 14.25 58%
Ka-band 20.2 21.2 20.7 30 31 30.5 63%
Max TX Power Level (dBm): Take care in setting the Max TX Power level. Although tempting
to simply allow the modem to TX up to it’s maximum capability in doing so you are taking far more
risk than is necessary and can seriously damage equipment or take down the network. As
mentioned above, fade comes in many forms and if for example cables on the RX chain were
slowly deteriorating or the antenna was slightly pointed incorrectly, the demod will see all of this
as fade and try to compensate by changing the uplink power. In a clear sky condition with bad
RX cables a demod seeing a fade will increase the power to try to compensate for this fade up to
the maximum power set in this parameter. For this reason it is best to take some time and
determine how much total rain and thus how much total UPLINK fade the site could actually see
and to calculate the maximum amount of uplink power needed to illuminate the satellite in worst
fade conditions. In doing so you will reduce the impact of other fade conditions.