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User Reference and Installation Guide
3-12
© 2006 Microwave Data Systems Inc. All Rights Reserved.
MDS FOUR.9 Series
05-4561A01, Rev. A
Select the Grounding Location for both the ODU and SDIDU
TM
: The units must be properly
grounded in order to protect them and the structure they are installed on from lightning damage.
Final ODU/SDIDU
TM
installation requires:
•
Grounding all ODUs as specified by supplier
•
Grounding all SDIDUs
TM
to the rack
•
Confirming the Presence of DC Power for the SDIDUs
TM
3.6.3
Critical System Calculations
3.6.3.1
Received Signal Level (RSL) and Link Budget
The received signal level (RSL) can be estimated using the following formula:
RSL (dBm) = P
TX
+ G
TX ANT
– L
Path
+ G
RX ANT
Where: P
TX
is the transmitter output power (in dBm)
G
TX ANT
is the gain of the transmit antenna (in dB)
G
RX ANT
is the gain of the receive antenna (in dB)
L
Path
is the Path loss, defined by:
L
P
(dB) = 36.6 + 20log
10
(F*D)
Where: F is the Frequency in MHz (4900 GHz), D is the Distance of path in miles
This link budget is very important in determining any potential problems during installation. The
expected RSL and measured RSL should be close (+/- 5 to 10 dB)
3.6.3.2
Fade Margin Calculation
The fade margin is the difference between the actual received signal and the MDS FOUR.9
Series Radio’s threshold for the modulation mode selected. The fade margin can be used to
determine availability and should be at least 10 dB.
3.6.3.3
Availability Calculation
Availability of the microwave path is a prediction of the percent of time that the link will operate
without producing an excessive BER due to multipath fading. Availability is affected by the
following:
•
Path length
•
Fade margin
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