SCAN TABLES
OVERVIEW OF SCAN TABLES
128 ENVOY™ TRANSCEIVER REFERENCE MANUAL
Overview of scan tables
A scan table is a notional grouping of channels stored in a transceiver. The number of
scan tables that you can add in your transceiver varies depending on the transceiver
type and options installed, however, only 100 channels may be scanned at any one
time.
Each scan table has a name, a scan on/off switch, a voice detect on/off switch, a
channel dwell time, and a data detect on/off switch.
The same channel may be included in one or more scan tables. One or more scan
tables may be allocated to an HF network. The same scan table may be allocated to
different HF networks.
NOTE: The default channel dwell time for a Selcall HF network is
0.25 sec/channel. The default channel dwell time for an ALE/CALM
HF network is 0.125 sec/channel.
NOTE: If the channels are scanned for voice, the channel dwell time defaults
to 0.55 sec/channel regardless of the type of HF network. If you are
using the 2.4 kbit/s Data Modem or 3012 compatibility mode in other
modems in a scanning Selcall system, the channels must be scanned for
data. In this case, the channel dwell time defaults to 0.6 sec/channel
regardless of the type of HF network.
The grouping of the channels enables the transceiver to perform common operations
on the included channels.
In order that a channel or group of channels is scanned, the following must occur:
• the channel must be included in a scan table
• the scan table must be set up to be scanned
• the transceiver must have scanning switched on
If the Global value is selected for an HF network, then all channels are scanned when
the transceiver is scanning, regardless of any scan tables.
When a transceiver is scanning, it is listening for a voice/data signal, a preamble
signal, or both. The transceiver listens for a pre-determined dwell time on each
channel. If it detects a preamble signal, it waits to hear the address of the station to
which the call is addressed. If the address sent matches one of the self addresses of the
listening station, it switches off scanning and mute (if they are not already switched
off).
It is recommended that scanning is switched on when you are not using the transceiver
to communicate. This ensures that you can receive calls from stations using the
channels that your transceiver is scanning.
Figure 41 shows the information that is stored for a scan table. Each item is described
in detail in the sections following.
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