GE MDS iNET 900, Reference Manual

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05-2806A01, Rev. J iNET Series Reference Manual 137
• Do not connect a radio to a power supply that is already pow-
ered up, unless necessary (that is, when connecting a radio to a
battery bank and charger). When power is applied by switching
on a power supply, the rise time of the supply is too slow to
cause overshoot.
• Typically, there are multiple return paths for the negative side
of the power supply, through the coaxial cable shield and the
chassis, for example. Any imbalance in the currents in the
power cable results in voltage overshoot, so this should be min-
imized during initial power-up if the supply cannot be turned
off.
• Add a 1 to 2
Ω
, 2 Watt resistor in series with the positive lead.
This greatly limits voltage overshoot. Since these radios draw
very little current in receive mode, and transmit only briefly,
there is little loss in power efficiency. In transmit, the voltage
drop is minimal and has no effect.
• Minimize the length of the power cabling, within reason.
• When power is applied from a power source having a relatively
high (1 or 2
Ω
) source impedance, or from a power source with-
out a large amount of output capacitance, no overshoot occurs.
Therefore, use a power supply that is rated appropriately for the
radio if possible—avoid using power supplies that far exceed
the radio's current requirements.
Please direct any questions you may have about interfacing to GE MDS
radios to the Technical Services Department, using the information pro-
vided at the back of this guide
.
4.2 RADIO (RF) MEASUREMENTS
There are several measurements that are a good practice to perform
during the initial installation. The will confirm proper operation of the
unit and if they are recorded, serve as a benchmark in troubleshooting
should difficulties appear in the future. These measurements are:
• Transmitter Power Output
• Antenna System SWR (Standing-Wave Ratio)
• Antenna Direction Optimization
These procedures may interrupt traffic through an established network
and should only be performed by a skilled radio-technician in coopera-
tion with the network manager.
4.2.1 Antenna System SWR and Transmitter Power
Output
Introduction
A proper impedance match between the transceiver and the antenna
system is important. It ensures the maximum signal transfer between the