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4 Tighten the tension nut on tuning screw 2 to at least 12 in-lb and fine-tune tuning screw 2 for a
PEAK.
5 Keep the tuning probe in cavity U2 and adjust tuning screw 3 for a DIP.
6 Tighten the tension nut on tuning screw 3 to at least 12 in-lb and fine-tune tuning screw 2 for a
DIP.
7 Insert tuning probe into cavity U3. Decrease output from the signal generator to –5 dBm.
8 Adjust tuning screw 4 for a DIP.
9 Tighten the tension nut on tuning screw 4 to at least 12 in-lb and fine-tune tuning screw 4 for a
DIP.
5.10
Tuning a Duplexer
Duplexer modules shipped with base radios are tuned at the factory. If a duplexer must be replaced in
the field, the unit must be installed and tuned specifically to the transmit and receive frequency pair for
the particular base radio.
5.10.1
Field Tuning Overview
NOTICE: These tuning procedures are valid for channels with a bandwidth of 200 kHz or less. If
bandwidth is more than 200 kHz, the duplexer must be tuned by the Motorola Solutions Support
Center (SSC).
The duplexer module is composed of three low-pass/high-notch cavities and three high-pass/low-notch
cavities. Each set of three cavities provides bandpass filtering for either the transmit RF signal or the
receive RF signal. In general, the duplexer must be tuned so that the transmit cavity set passes the
transmit signal and rejects the receive signal; concurrently, the receive cavity set must be tuned to
pass the receive signal and reject the transmit signal.
Tuning is performed by injecting RF signals and making tuning adjustments (using the tuning rods and
trimmer screws) while monitoring for maximum or minimum readings on the RF millivoltmeter. Field
tuning the duplexer module requires the following general adjustments:
•
Tune high-pass/low-notch cavities for maximum pass and reject response
•
Tune low-pass/high-notch cavities for maximum pass and reject response
•
Check high-pass/low-notch and low-pass/high-notch cavities for insertion loss
•
Check high-pass/low-notch and low-pass/high-notch cavities for isolation
5.10.2
Required Test Equipment
Tuning of the duplexer module requires the following test equipment:
•
RF Signal Generator - Aeroflex 3900 Series Service Monitor (or equivalent)
•
RF Millivoltmeter (Boonton 92E or equivalent)
•
50 Ohm N-type terminator
•
Tuning tool (5/32-inch x 4-inch screwdriver) (UHF)
•
Male-to-Females N-Type "T" connector (UG-107B/U or equivalent) (VHF)
•
Slotted screwdriver (VHF)
•
3/32-inch Allen wrench (VHF)
Chapter 5: GTR 8000 Base Radio Optimization
MN003286A01-E
165
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Table of Contents
Troubleshooting
