- Power High/Low: Changes the equipment from full power (25 watts
on a fixed set) to low power (1 watt). Full power on a hand-held VHF
set is normally 4-5 watts, low power also 1 watt.
Dual Watch: Allows you to monitor Channel 16 at the same time as
one other channel of your choice. Normal procedure is to select the
working channel (not Ch 16) then activate dual-watch. If Signals are
received on Ch16, your equipment lets you hear those Signals (so you
should hear any emergency communications, even when monitoring
some other channel). (Note: with Dual Watch on, you may not be
able to use any other control except the 'quick Ch16' button).
- If you do hear emergency communications on Ch16, press the
'quick Ch16' button to remove Dual Watch and put you onto
Channel 16 with full power, before transmitting any response and/
or to receive further information.
Dimlbacklight: Adjusts the level of illumination on the screen/controls.
The basic controls listed above, available on all manufacturer's
equipment, may be supplemented by others including:
- Scan: Allows you to 'scan' more than two channels. Helpful now that
vessels at sea should be monitoring Ch16 and Ch13 - if you also
want to monitor some additional channel (e.g., an intership channel,
or a Port Operations channel); (Note: you do not have to include
Ch70 here - that watch is kept by the separate Ch70 Watch Receiver);
US/INT: Allows you to switch between 'INTernational' Channel
configuration to 'United States' Channel configuration, when in the
waters around North America. Most marine VHF channels are the same
for both INT and US, but the US Coast Guard, and the Canadian Coast
Guard, both use some channels that differ from the International settings
- including 'weather' channels (Wxl, Wx2 etc - see Chapter 2) used
by the USA and Canadian authorities to broadcast continuous weather/
navigation information and which are not available on the INT setting.
Question: You said earlier that VHF propagation was line of Sight
and that the range achievable depended on the height of antennas. If
that is the case, why do I only achieve a few miles range on low power
but, on high power, I can talk to the same vessel/coast station at much
greater range?
Answer: The power radiated from your antenna, with the equipment
set at 1 watt, is too low to 'lift the squelch' on VHF receivers more than
a few miles away. Power reduces with distance from transmitter antenna.
MARINE COMMUNICATIONS 131