Calculating System Gain - Microwave Data Systems iNet 900 Quick Start Manual

12

Calculating System Gain

To determine the maximum allowable power setting of the radio, per-
form the following steps:
1. Determine the antenna system gain by subtracting the feedline loss
(in dB) from the antenna gain (in dBi). For example, if the antenna
gain is 9.5 dBi, and the feedline loss is 1.5 dB, the antenna system
gain would be 8 dB. (If the antenna system gain is 6 dB or less, no
power adjustment is required.)
2. Subtract the antenna system gain from 36 dBm (the maximum
allowable EIRP). The result indicates the maximum transmitter
power (in dBm) allowed under the rules. In the example above, this
is 28 dBm.
3. If the maximum transmitter power allowed is less than 30 dBm, use
one of the transceiver's control tools as described in PROGRAM-
MING on page 21 to set the power accordingly.
For convenience, Table 4 lists several antenna system gains and shows
the maximum allowable power setting of the radio. Note that a gain of 6
dB or less entitles you to operate the radio at full power output—30 dBm
(1 watt).
Table 4. Antenna system gain vs. power output setting (USA)
Antenna System Gain
(Antenna Gain in dBi*
minus Feedline Loss in dB†)
6 (or less)
* Most antenna manufacturers rate antenna gain in dBd in their
literature. To convert to dBi, add 2.15 dB.
† Feedline loss varies by cable type and length. To determine the
loss for common lengths of feedline, see Table 3 on page 11.
For details on how to set the power level via the Ethernet/HTTP inter-
face, See "Programming Via an HTTP/Web Browser" on page 22 for
details.
MDS iNet 900 Installation Guide
DRAFT 6—8/29/01
Maximum Power
Setting
(in dBm)
30
8 28
10 26
12 24
14 22
16 20
EIRP
(in dBm)
36
36
36
36
36
36
MDS 05-2873A01, Rev. A