Mitsubishi FZ-991A ETACS Power Amplifier

ETACS Power Amplifier
ETACS Power Amplifier

Here’s a blast from the past, before the time of GSM networks. This is a power amplifier from an Analogue mobile phone, on the ETACS system. This unit will output, according to the TACS standard, about 10W of RF power in the 900MHz band. RF connections on this unit are made via TNC connections, and a DIN connector for power & control. This unit is made of solid aluminium, no plastic casing here! The metal is needed for both RF shielding, and heatsinking capability for the power amplifier module inside.

Rating Label & Control
Rating Label & Control

Here’s the rating label, and the control connector.

Cover Removed
Cover Removed

Removing 4 screws allows the lid to be removed from the cast base. There’s RF shielding gasket around the edge of the lid, along with the internal sections of the amplifier. The board is pretty sparsely populated. RF input is via the short cable on the left, and output to the antenna on the lower right.

Bare PCB Top
Bare PCB Top

A few more screws & the PCB comes out of the cast base.

Bare PCB Bottom
Bare PCB Bottom

Not much on the bottom of the board, apart from a lot of via stitching & passive components.

RF Section Tracks
RF Section Tracks

Under the RF section is very dense with passives, and via stitching to separate the sections.

Voltage Regulator
Voltage Regulator

There’s a 7v linear regulator near the power input connection, most likely to provide a biasing supply for the RF power section.

Amplifier Section
Amplifier Section

The main power amplifier is a Hitachi PF0012 module, these were very common in radios, and contain all the components required for an RF PA stage. I couldn’t find a specific datasheet for this module unfortunately. There are some support components inclusing a NMJ2901 Quad comparator from JRC, and a MC14051B Analogue Mux/Demux.

Duplexing Filters
Duplexing Filters

Filtering of the TX & RX frequencies is done by this pair of units from MuRata

Antenna Duplexer
Antenna Duplexer

Finally, there’s an antenna duplexer on the output side, also from MuRata. Unfortunately no datasheets available for any of these parts.

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