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5
FIELD TUNING PROCEDURE
Duplexer modules shipped with stations 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 station.
Field Tuning Overview
CAUTION
68P81085E16-B
09/30/05
The duplexer module is comprised 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 pass-
es the transmit signal and rejects the receive signal; concurrently, the re-
ceive cavity set must be tuned to pass the receive signal and reject the
transmit signal.
This tuning procedure is valid for channels with a bandwidth of 200kHz
!
or less. If bandwidth is more than 200kHz, the duplexer must be tuned
by the service depot.
Tuning is performed by injecting rf signals and making tuning adjust-
ments (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 re-
sponse
•
Tune low-pass/high-notch cavities for maximum pass and reject re-
sponse
•
Check high-pass/low-notch and low-pass/high-notch cavities for in-
sertion loss
•
Check high-pass/low-notch and low-pass/high-notch cavities for
isolation
VHF Duplexer Module
9
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