Notes On Using 28 Vdc Power Supplies - GE MDS iNET 900 Reference Manual

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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, set
the power to the desired level using the Management System.
(
Main Menu>>Radio Configuration>>RF Output Power Setpoint
For convenience, Table 4-3 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 (28.7 dBm for iNET-II).
Table 4-3. Antenna System Gain vs. Power Output Setting
Antenna System Gain Maximum Power Setting
(Antenna Gain in dBi*
minus Feedline Loss in dB†)
Omni 6 (or less)
Omni 11.14
* Most antenna manufacturers rate antenna gain in dBd in their litera-
ture. 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
For assistance in the conversion of dBm to Watts, see
dBm-WATTS-VOLTS CONVERSION CHART on Page 143.

4.1.9 Notes on Using 28 VDC Power Supplies

Common 28 Vdc supplies are often high-current power supplies
designed primarily to charge battery banks. The radio can be operated
from these supplies, providing there are no transients on the leads as
power is applied to the radio. Transients can be created that rise above
30 Vdc to a voltage that exceeds the primary voltage rating of the radio
and can destroy its voltage regulators and other components. It is impor-
tant to keep this potential hazard in mind when designing 28 Vdc power
supply connections for the radio.
• Use a two-conductor cable to power to the radio. Then the cur-
rents in the positive and negative wires are equal and opposite,
causing their magnetic fields to cancel. The result is no net
inductance in the connection to cause voltage overshoot.
iNET Series Reference Manual
Maximum Power Setting
(PWR command)
iNET Radio
30
24
Table 4-1 on Page 134
)
(PWR command) EIRP
iNET-II Radio (in dBm)
28
23
.
05-2806A01, Rev. J
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