User's Manual

Cable loss = 1 dB
Fixed pad at modem = 20 dB
Input to Cable Modem= --45 dBm=+4 dBmV
Note: 0 dBm @75Ω=+49 dBmV
In the above example, the received signal is –+4 dBmV.
The typical
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Cable Modem Receive Sensitivity is –15 dBmV to +15 dBmV at 64
QAM, so the Fade Margin is 4+15=19 dB.
Links are generally considered to be good with 10 or 20 dB Fade Margin, so this
is excellent.
The Free Space Path Loss comes from the formula in Figure 10-7.
Loss
5GHz band
=112 + 20*log(miles)
LOSS
Loss (dB)
100.0
110.0
120.0
130.0
0.25 1.25 2.25 3.25 4.25 5.25 6.25 7.25
Distance (Miles)
Figure 10-7: Free Space Path Loss at 5GHz.
10.5 Availability
Classical microwave formulas also address the Availability of a link. The
Availability is the percent of the time the link meets its performance specification,
usually measured in Bit Error Rate or Packet Error Rate. Measured on a yearly
basis, the Availability is simply the percent time the link does not have an
Outage. An Outage is usually a 10-second interval in which the performance
falls below a set level.
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D-Link model 200 data sheet from www.dlink.com
ARCXtend manual, August 2003 10-7