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VHF Fundamental Info
The VHF Channel System
The VHF radio telephony system uses a limited number of frequen-
cies called channels. The public system has 57 channels, numbered
CH 1 to 28 and 60 to 88, each of which has a certain purpose:
intership, ship-to-port, or ship-to shore (public). You can have private
channels, too. In US waters, the channels are different. Therefore
you need to set the system to “US” channels there. Other waters like
the Rhine have their own different systems, too.
Four channels have special purposes:
16:
To be used for verbal distress calls and for calling “all
stations”
only. All large ships are obliged to monitor it
constantly. Never to be used for chatting, etc.!
70:
The DSC channel, see below.
75-76: Used as Guard Band for distress channel 16.
Verbal VHF Communication
All channels except channel 70 are used for verbal communication.
There are two types of channels, simplex and duplex:
-
On a simplex channel, both parties transmit and receive on the
same frequency. Therefore you cannot talk and listen at the
same time. When you have finished talking, say “over”, and
release the handset’s PTT key.
-
On a duplex channel, you talk and listen on two different
frequencies. You can therefore speak and listen at the same
time. To save power, release the handset’s PTT key except when
talking.
Note that everybody with a VHF receiver can listen to your conversa-
tion, but it is forbidden to use or pass on what is heard.
DSC Digital Communication
DSC is a digital data transfer system using VHF CH 70. The
transmitter waits until the channel is free and then sends its data,
either to a designated address, or to “all stations” for example for a
DSC distress call. It is mainly used for getting in contact in order to
establish verbal communication.
Telephony display
Normal display
Scanning display
DUP
25W
DW
INT
MEM VOL SQ
12
1 10 03
TX Power indicator
INT/US mode indication
Speaker On/Off
Dimmer
25W
INT
MEM P-CH
Pr -
7 ALL 16