Moderated Discussion Areas
ContinuousWave: Small Boat Electrical
VHF Ship Station Transmitter Power
|Author||Topic: VHF Ship Station Transmitter Power|
posted 04-11-2014 11:10 PM ET (US)
The maximum power for a ship station transmitter in the VHF Marine Band is given in
47 CFR 80.215 - TRANSMITTER POWER.
and is mentioned in several subparts.
In subpart (e):
In subpart (g):
The manufacturers of VHF Marine Band radios often specify the power output of their radios at 13.8-Volts DC, which is 0.1-Volt higher than the FCC specification. I believe they do this because this will, when the radio is operated at the FCC specified maximum voltage maximum of 13.7-Volt. cause the power output to not exceed 25-Watts.
Subpart (g) goes on to say:
For the technically curious, the channel numbers for the mentioned frequencies are
156.375-MHz = 67
Channels 67 and 13 are designated as Bridge-to-Bridge communication—that is ship bridge to another ship bridge or a highway bridge—and are usually used at 1-Watt, but they can be changed to full power.
Channels 75 and 76 are the channels adjacent (in frequency) to Channel 16, the distress, safety, and emergency calling channel, (156.800-MHz), and limiting power to 1-Watt is mandatory and cannot be overridden by the operator. This provides a bit of a guard channel so that a nearby station operating on 75 or 76 would not desensitize or interfere with a receiver tuned to 16. I believe at one time no transmission was permitted on those channels. (I have a c.2001 radio, and it does not provide those channels.)
posted 04-12-2014 10:11 AM ET (US)
A fixed-mount VHF Marine Band radio must produce more than 8-Watts but no more than 25-Watts power output, and must contain automatic power reduction to 1-Watt on certain channels, but permit override to full power on some of them.
A hand-held or portable VHF Marine Band radio must produce no more than 10-Watts, and is exempted from some of the automatic power reduction regulations.
If the radio transmitter is operated from a lead-acid storage battery, the power output is to be measured when the supply voltage is in the range of 12.2 to 13.7-Volts.
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