GE MDS MDS iNET 900, Reference Manual

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140 iNET Series Reference Manual 05-2806A01, Rev. H
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
radio and antenna. The impedance match can be checked indirectly by
measuring the SWR (standing-wave ratio) of the antenna system. If the
results are normal, record them for comparison for use during future
routine preventative maintenance. Abnormal readings indicate a pos-
sible trouble with the antenna or the transmission line that will need to
be corrected.
The SWR of the antenna system should be checked before the radio is
put into regular service. For accurate readings, a wattmeter suited to
1000 MHz measurements is required. One unit meeting this criteria is
the Bird Model 43
™
directional wattmeter with a 5J element installed.
The reflected power should be less than 10% of the forward power
(
≈
2:1 SWR). Higher readings usually indicate problems with the
antenna, feedline or coaxial connectors.
If the reflected power is more than 10%, check the feedline, antenna and
its connectors for damage.
Record the current transmitter power output level, and then set it to
30 dBm for the duration of the test to provide an adequate signal level
for the directional wattmeter.
Procedure
1. Place a directional wattmeter between the
ANTENNA
connector and
the antenna system.
2. Place the transceiver into the Radio Test Mode using the menu
sequence below:
(Main Menu>>Maintenance Menu>>Radio Test>>Test Mode>>Y>>ON)
NOTE: The Test Mode has a 10-minute timer, after which it will return
the radio to normal operation. The Radio Test Mode can be
terminated manually by selecting
OFF
on the menu or tempo-
rarily disconnecting the radio’s DC power.
3. Set the transmit power to 30 dBm. (This setting does not affect the
output level during normal operation—only during Test Mode.)
(Main Menu>>Maintenance Menu>>Radio Test>>Test Mode>>Tx Power Out-
put)
4. Key the transmitter.
(Main Menu>>Maintenance Menu>>Radio Test>>Test Mode>>TxKey>>
Enable)