User Guide

After Sales
Technical Documentation
TACS System Overview
Original, 09/94Page 6
Voice Channels
Voice channels are used for both conversation and data transfer such as
Hands–off, Telephone Output Power Control and special local control
features.
Data transfer between the Cell Site and the telephone is at a rate of 8
kbits/s using FM. Data is formatted into groups of words with a binary
preamble for synchronization purposes.
Tone Signalling
In addition to Digital Signalling, two signalling methods are used; a
Supervisory Audio Tone (SAT) and a Signalling Tone (ST). The SAT is
one of three frequencies centered on 6kHz, generated and sent by the
Cell Site. The received SAT signal is transponded by the telephone on its
assigned voice channel and is used to verify that the telephone is tuned to
the assigned base station.
The Signalling Tone is a 8kHz tone generated and sent by the telephone
on the assigned voice channel. It is used to acknowledge various cell site
commands by varying the duration of the tone. For example, an ST of
50ms duration is decoded by the cell site as an acknowledgement of the
Hand–off command.
Power–up Mode
On powering up, the telephone reads the fixed data in its memory before
scanning the control channels. It selects and tunes to the control channel
with the greatest signal strength and from this it receives the overhead
control message. The message informs the telephone of the system to
which it is tuned and the range of channels to scan for paging and access.
Idle Mode
The telephone scans the paging channels and selects and tunes to the
strongest one, on which it receives continuous overhead and paging
messages. The paging messages notify the telephone of incoming calls.
From this point the telephone continuously updates stored overhead
message and monitors paging messages until it decodes its own
telephone number, at which time it tunes to the strongest of the
designated access channels.