3 - 2 MTH800 TETRA Handportable Terminal / Basic Service Manual Description
Description
Transceiver Description
All the terminal circuitry is contained in the Digital/RF Board and the keypad
board. The Digital/RF board is divided into the following sections: digital,
frequency generating, transmitter, and receiver.
Digital Section Description
The digital section includes the Patriot IC that consists of the Mcore risk machine
and the Digital Signal Processor (DSP).
The Mcore is the controller of the Digital/RF Board. It controls the operation of the
transmitter, receiver, audio, and synthesizer integrated circuits located in the RF
section. It communicates with the keypad and display.
The Digital Signal Processor (DSP) performs modulation and de-modulation
functions for the terminal. It also performs Forward Error Correction and other
correction algorithms for overcoming channel errors and ACELP speech coding.
It carries out linear 10-bit analog to digital conversions, audio filtering, and level
amplification for the microphone audio input and the received audio output.
The power and audio section is based on the GCAP III and includes power
supplies, 13-bit CODEC, audio routing, microphone and ear piece amplifiers. A
audio power amplifier is used for the loud speaker.
Transmitter Path Description
The transmitter circuitry includes a linear class AB Power Amplifier (PA) for the
linear modulation of the MTH800. It includes a cartesian feedback loop to
enhance its transmitter linearity and reduced splattering power into adjacent
channels.
The transmitter path consists of a cartesian feedback loop that contains the
forward and loop feedback paths.
The forward path includes the JAVELIN IC, BALUN, Attenuator, Power Amplifier
and Isolator.
The loop feedback path includes the directional coupler, attenuator, BALUN, and
JAVELIN IC.
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