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HF NETWORKS

ENTRIES FOR AN HF NETWORK

144 ENVOY™ TRANSCEIVER REFERENCE MANUAL

Global

An HF network typically has channel information associated with it in the form of

scan tables. If you want the HF network and self address to be used to make and

receive calls on any channel that is programmed in the transceiver, select the On

check box for the Global entry.

Preamble

Preamble may be used in HF networks that use the Selcall and ALE/CALM call

systems only. When you make a call to a specific station or group of stations, the

addresses of those stations are sent in a preamble signal before the call is established.

Transceivers that are scanning listen for the nominated dwell time on each channel

that is being scanned. If the transceiver detects a preamble signal, it pauses scanning

and determines if its address is in the preamble. If an address in the preamble matches

the self address of the listening station, and it has a matching call system, the station

switches off the scan and mute, ready to establish the call with the other station. If

there is no matching address in the preamble, the listening station resumes scanning.

The preamble that is sent must be transmitted for a period of time greater than or equal

to the channel dwell time multiplied by the number of channels being scanned in the

transceiver that is being called.

Preamble length

The length of preamble that is sent with a call is dependent on the number of channels

being scanned in the listening station, and the channel dwell time. If you select the

Auto value for the preamble length, the transceiver calculates this value for you.

When a transceiver calculates the preamble length automatically, it assumes that the

transceiver at each station is set up similarly. The length of preamble sent at the

beginning of a call is calculated from the information from the scan tables associated

with the HF network used for the call. If the communicating systems are set up

identically, then this information provides the exact duration of preamble required to

cover the scan cycle. The transceiver sums the total channel dwell time for each scan

table allocated to the HF network.

If you are calling a station that uses identical HF network information, the preamble

of the calling station matches the detection requirements of the called station.

Codan Envoy Reference Manual

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