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9-28 MTR3000 Radio Frequency Distribution System (RFDS) Equipment: Field Tuning Procedures

9.5.2 Duplexer

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 base station/repeater.

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

passes the transmit signal and rejects the receive signal and, at the same time, 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 pass

and notch 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

9.5.2.1 Duplexer Tuning Procedure (with basic instruments)

9.5.2.1.1 Test Equipment

The following test equipment are required to properly tune the duplexer module:

• Aeroflex 3900 Series Communications System Analyzer (or equivalent)

• RF Millivoltmeter (Boonton 92E or equivalent)

• RF Signal Generator (HP8565B or equivalent)

•50 Ω N-type terminator

• Tuning tool; 4 mm x 10.1 cm (5/32" x 4") screwdriver

• N-to-N bullet connector (UG29A/U or equivalent)

• 11 mm (7/16") Nutdriver

• 11 mm (7/16") Open End Wrench

• N-to-BNC Adapter (UG349A/U)

• N-to-N Connector (UG57B/U)

Note

The 800 MHz duplexer module is fixed and does not require tuning.

This tuning procedure is valid for channels with a bandwidth

of 200 kHz or less. If the bandwidth is more than 200 kHz, the

duplexer must be tuned by the service depot.

Motorola MTR3000 Basic Service Manual

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