Overview; General; Digital Modulation Technology - Motorola MTH500 Service Manual

General

Digital Modulation Technology

68P02963C70-O
To achieve a high spectrum efficiency, the
technology and sophisticated voice-compression algorithm. The voice of the per-
son speaking into the microphone is converted into a digital bit stream consisting
of zeros (0) and ones (1). This stream is then modulated into a radio-frequency
(RF) signal, which is transmitted over the air to another radio. The process is
called digital modulation.
MTH500
The is a 380-400 MHz portable radio that can operate in dispatch and
phone mode. This radio can also operate in TMO (Trunked Mode Operation) and
DMO (Direct Mode Operation). It uses two digital technologies: p/4DQPSK and
Time Division Multiple Access (TDMA).
p/4DQPSK is a modulation technique that transmits information by altering the
phase of the radio frequency (RF) signal. Data is converted into complex symbols,
which alter the RF signal and transmit the information. When the signal is re-
ceived, the change in phase is converted back into symbols and then into the orig-
inal data.
The system can accommodate 4-voice channels in the standard 25 kHz channel as
used in the two-way radio.
Time Division Multiple Access (TDMA) is used to allocate portions of the RF sig-
nal by dividing time into four slots, one for each unit.
Time allocation enables each unit to transmit its voice information without inter-
ference from other transmitting units. Transmission from a unit or base station is
accommodated in time-slot lengths of 15 milliseconds and frame lengths of 60
milliseconds. The TDMA technique requires sophisticated algorithms and a dig-
ital signal processor (DSP) to perform voice compressions/decompressions and
RF modulation/demodulation.

Overview

MTH500
uses digital modulation
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