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3-6 Theory of Operation

3.2.3 Output Board

The Output Board is a replaceable module within the PA, and contains the harmonic filter, directional

couplers, and surge suppression circuitry within the PA. The Output Board circuitry is denoted by

reference designators in the 8000’s (i.e. R8000, C8450, etc). The Output Board connects the

isolator output to the PA N-Type output connector that is mounted to the PA cast heat sink.

3.2.3.1 Harmonic Filter

The harmonic filter is located following the isolator stage of the PA. This filter attenuates the

harmonic energy created by the final amplifier stage prior to reaching the antenna port. The

harmonic filter will be fully distributed for some frequency bands and will contain lumped elements

(capacitors and inductors) for other frequency bands, but will be located in the same location for all

bands.

3.2.3.2 Directional Couplers

The forward and reverse directional couplers on the output board utilize edge-coupled lines and

isolation loads with a coupling coefficient of approximately 30 dB, and perform a diode rectification

of the coupled RF signal to provide a DC voltage back to the distribution board that will be routed to

the A/D for metering. The forward power sensor voltage is also tied into the power control loop, and

is used to balance the loop for the desired output power.

3.2.3.3 Surge Suppression

For suppression of surges entering the PA output port, an air-wound inductor is placed between the

output line and ground to provide a high impedance within the specified frequency band of the PA.

During a surge event such as a nearby lightning strike, this will reduce the energy entering the PA

output port prior to reaching other PA internal components, and help to prevent damage during

these types of events.

3.2.3.4 Module I/Os

RF_IN (M8002) – RF input from the isolator output

RFOUT (M8000) – RF output to the antenna port

REV_DET (M8001) – Reverse power sensor output to Distribution Board

FWD_DET (M8003) – Forward power sensor output to Distribution Board

3.2.4 Distribution Board

The Distribution Board is a replaceable module within the PA, and contains the PA SPI circuitry,

diagnostic metering circuitry, RF power control circuitry, and the fan supply. The Distribution Board

circuitry is denoted by reference designators in the 6000’s (i.e. R6000, C6450, etc).

A 10-pin signal connector (J6000) is located on this board and is the external interface to the

backplane through a ribbon cable for communication with the SCM. A 6-pin power connector

(J6001) is also located on this board and is the interface to the PS for supplying main supply bus

voltages to the PA, with 2 pins dedicated to 28.6 V, 2 pins for 14.2 V, and the other 2 pins are ground

Motorola MTR3000 User Manual

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