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Author Topic:   VHF Ship Station Transmitter Power
jimh posted 04-11-2014 11:10 PM ET (US)   Profile for jimh   Send Email to jimh  
The maximum power for a ship station transmitter in the VHF Marine Band is given in


and is mentioned in several subparts.

In subpart (e):

Ship stations frequencies above 27500 kHz. The maximum power must not exceed the values listed below.

(1) Ship stations 156–162 MHz—25W 6, 13

Marine utility stations and hand-held portable transmitters: 156–162 MHz—10W

6 Reducible to 1 watt or less, except for transmitters limited to public correspondence channels and used in an automated system.
13The frequencies 156.775 and 156.825 MHz are available for navigation-related port operations or ship movement only, and all precautions must be taken to avoid harmful interference to channel 16. Transmitter output power is limited to 1 watt for ship stations, and 10 watts for coast stations.

In subpart (g):

The carrier power of ship station radiotelephone transmitters, except portable transmitters, operating in the 156-162 MHz band must be at least 8 but not more than 25 watts. Transmitters that use 12 volt lead acid storage batteries as a primary power source must be measured with a primary voltage between 12.2 and 13.7 volts DC.

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:


Additionally, unless otherwise indicated, equipment in radiotelephone ship stations operating in the 156-162 MHz band must meet the following requirements:

(1) All transmitters and remote control units must be capable of reducing the carrier power to one watt or less;

(2) Except as indicated in (g)(4) of this section, all transmitters manufactured after January 21, 1987, or in use after January 21, 1997, must automatically reduce the carrier power to one watt or less when the transmitter is tuned to 156.375 MHz or 156.650 MHz, and must be provided with a manual override switch which when held by an operator will permit full carrier power operation on 156.375 MHz and 156.650 MHz;

(3) Except as indicated in (g)(4) of this section, all ship station transmitters installed after January 9, 2006, must be capable of tuning to 156.775 MHz and 156.825 MHz and must automatically reduce the carrier power to one watt or less, with no manual override capability, when the transmitter is tuned to either 156.775 MHz or 156.825 MHz;

(4) Hand-held portable transmitters are not required to comply with the automatic reduction of carrier power in (g)(2) of this section; and

(5) Transmitters dedicated for use on public correspondence duplex channels as additional equipment to a VHF ship station in the Great Lakes which meet all pertinent rules in this part are not required to reduce their carrier power to one watt.

For the technically curious, the channel numbers for the mentioned frequencies are

156.375-MHz = 67
156.650-MHz = 13
156.775-MHz = 75
156.825-MHz = 76

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.)

jimh posted 04-12-2014 10:11 AM ET (US)     Profile for jimh  Send Email to jimh     
To summarize:

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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