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VHF Marine Band Radio Installation on a Small Boat

by James W. Hebert

When installing a VHF Marine Band radio on a small boat there are several elements to consider, including:

All of these topics are briefly reviewed below, and supplemental articles with information in greater depth are suggested with hyperlinks.


Generally speaking, all radio transmitters in the USA must be licensed by the FCC. For most recreational boaters, their VHF Marine Band ship radio transmitter will be licensed by-rule, that is, it will not be necessary to obtain an individual FCC-issued ship station license. A ship station is licensed by rule and does not need a separate ship station license from the FCC if:

Unless you are a recreational boater in a border region, you will likely qualify for a ship station license by-rule. If your boating is in border regions, and your boat does travel to foreign ports (such as Canada) you will probably need to obtain a ship station license from the FCC. A separate article explains the process of applying for, paying for, and obtaining an FCC ship station license.

VHF Marine Band radios are generally only for use aboard boats. Use of a marine radio from shore requires an FCC-issued shore station license. Usually only marinas, towing companies, or regulatory agencies are granted shore station licenses. This restriction applies to use of hand held Marine Band radios on shore, too. However, a recent revision to the FCC regulations does permit limited use of handheld radios on shore under particular circumstances and in particular places.

At one time, the operation of most radio transmitters in the USA required an operator's license or permit. Over time, this requirement has been eliminated in many radio services. For recreational boats with a voluntarily-equipped VHF Marine Band transmitter, the FCC has, for the most part, eliminated the need for an operator's license. If your recreational boat with a voluntarily-equipped VHF Marine Band transmitter qualifies for a ship station license by-rule, a companion operator's license is not required. However, in order to comply with treaty provisions with foreign nations, if you operate your U.S.A boat in the waters of a foreign nation, you will likely be required to have an FCC-issued operator's license to satisfy the reciprocal licensing agreement with that nation. The experience of many boaters when visiting Canada tends to suggest that enforcement of these licensing provision is not very strict there, but, even so, it will be prudent to comply with the rules. Obtaining the appropriate operator's license is really just a formality. The applicant pays a fee--a rather stiff one--and swears he knows the rules for operation. There is no examination to be taken and passed. The most difficult part is completing the license application and paying the fee. If you can do that, you can obtain the necessary license, but it would also be a good idea to actually be familiar with the regulations you are required to adhere to. A good overview of FCC licensing for the VHF Marine Band service is found at the FCC's own website.

Equipment Compliance

Beginning in March 2011, the FCC prohibited the importation, manufacture, sale, or installation of fixed-mount VHF Marine Band digital selective calling radios that do not comply with ITU-R Rec. M.493-11 CLASS-D standards. More details about FCC-required radio DSC specifications can be found in a companion article. Regulations about VHF Marine Band radio transmitter power output are described elsewhere.

The FCC has clarified their position regarding previously-installed radios; they can continue to be used. Re-use of older radios should be weighed in consideration to the modest cost of a new and better radio. After March 25, 2015 these same prohibitions apply to portable radios in the Marine Radio Service, as well. Because modern VHF Marine Band radios with digital selective calling to CLASS-D ratings are now available for very modest cost and they represent a significant step up from older radios, there is little economic or practical reason to continue to use out-dated radio equipment.

Maritime Mobile Service Identity

A digital selective calling (DSC) radio requires a maritime mobile service identity (MMSI). The MMSI identifies the ship making a transmission with DSC. A DSC radio cannot function without an MMSI. More information about obtaining an MMSI is found in a companion article.

A modern DSC radio (with CLASS-D rating) will not provide any DSC features unless an MMSI has been entered into the radio. The radio should also nag the operator to perform this procedure each time the radio is powered. Since an MMSI can be obtained at no cost (or in the case of applying for an FCC-issued ship station license, at no additional cost), there is little reason to not have an MMSI. To continually operate a modern DSC radio without an MMSI makes little sense.

Radio Location

The location of a VHF Marine Band radio on a small boat should be considered with reference to two other components: the compass and the antenna. Most radios have internal loudspeakers with permanent magnets. The magnetic field from the permanent magnet in the loudspeaker can cause the boat compass to deviate from its normal magnetic North indication. The radio should be installed several feet away from the compass. It is prudent to check for compass deviation caused by the radio before selecting a location for the radio.

The radio should not be installed in a location where the radio itself will be in the field of radiation from the antenna. When transmitting, radiation from the antenna can interfere with the operation of the transmitter itself, causing a problem known as RF feedback. It often manifests as a squealing sound on the transmitter modulation. The best practice is to have at least three feet of vertical separation between the radio and the base of the antenna. Three feet of horizontal separation may be sufficient, but not in all cases.

Radio DC Power

A typical 25-Watt fixed mount VHF Marine Band radio will require a circuit fused for about 7.5-Amperes when transmitting. The regulation of the supplied voltage should be very good. Transmitter power output is very proportional to operating voltage, and if the 12-Volt power sags to a lower voltage, the transmitter power will be reduced. The power for the radio should be clean power that is free of the AC-ripple voltages created by the alternator charging currents of the propulsion engine. The presence of alternator AC voltages on the radio power will produce a varying frequency whistle sound or whine on the transmitter modulation. Suppression of AC currents on the DC power can be enhanced by use of power line filters. Presence of large AC currents on a battery is often an indicator that the battery itself has degraded.

It is not necessary to connect a radio directly to the battery powering the radio, although many manufacturers include such advice. You may connect the radio power leads to a secondary power distribution panel, as long as the power available at the secondary power distribution panel has sufficient current, good voltage regulation, and is free of AC-ripple currents.

Antenna Transmission Line

The antenna used on recreational small boats for the VHF Marine Band radio will typically have a captive transmission line included. At the transmitter end of the transmission line a proper connector is needed, usually a PL-259 or equivalent connector. Some antennas provide the connector pre-installed, but some only provide a bare transmission line, leaving installation of the connector to the installer. The length of transmission line provided is usually in the range of 15 to 20-feet. If the transmission line has a pre-installed connector, there is little concern for cutting the transmission line to a shorter length, even if the installation allows for it. Leave the line intact, and coil any excess transmission line into a loose coil of about 4-inch diameter. If there is an excess of transmission line and no pre-installed connector, the transmission line can be cut to suit the length needed. Never cut the transmission line shorter than about 5-feet. Always leave at least 1-foot of slack near the radio to make service easier.

PL-259 Connector

Installation of a PL-259 connector seems to be a source of difficulty for many boaters. There are many types of connector available in addition to the standard PL-259. Some variations are solder-less connectors. For boaters who lack soldering equipment and soldering skill, use of a solder-less connector may be advantageous. In any connector installation, take particular care to not create any short circuits or open circuits in the connection.

Antenna Location

The base of the radio antenna should be mounted in a position to create the greatest possible height for the antenna. The height of the antenna has the greatest influence on the range of radio communication, and every effort should be made to locate the base of the antenna so as to increase height. The antenna should be at the minimum at least three feet away from the transmitter in the vertical direction. Installing the base of the antenna adjacent to the radio itself is a poor practice and should be avoided. Install the antenna so it is in the clear and away from other metal objects. The antenna should be oriented to be vertical, and not mechanically tilted away from vertical except for storage or when necessary to reduce vertical draft to pass under bridges. Mechanically tilting the antenna degrades the radiation pattern and reduces performance.

Antenna Selection

In general the VHF Marine Band antenna for a small boat will have to be proportionally small. Antenna length is not a significant factor in determining range of communication compared to antenna height. A shorter antenna that is mounted higher is preferred to a longer antenna mounted lower. An excellent antenna for a small boat is described in a companion article.

The gain that is claimed to be provided by longer antennas is only obtained in the main lobe of the antenna, and practical gain from the antenna is only obtained when the main lobe is oriented precisely in the desired direction. The cost of the gain in a concentrated lobe is a significant reduction in signal strength when not in the main lobe. Accordingly, on a boat in motion when that motion moves the antenna away from vertical, it is likely that the signal from a high-gain antenna could be lower in strength at a distant receiver than the signal from an antenna with lesser gain but a broader lobe. Except when a small boat is very stable in seas, it is unlikely the main lobe of a high-gain antenna will always be oriented in the most favorable direction.

Antennas with modest gain have broad radiation characteristics, and they will be less affected by boat movement. Longer antennas with higher gain have narrow beams of concentrated radiation that may not be helpful when a boat is in motion in the seas. A companion article has more information on the radiation pattern of antennas and how the signal strength varies as a function of degrees off-axis from the main lobe. The other article assesses typical radiation patterns and tabulates signal strength as a function of degrees off-axis. The results show that with a little as a 20-degree movement off-axis, the gain from 4-foot antenna exceeds the gain from an 8-foot antenna. At only 10-degrees off-axis, the gain of 4-foot and 8-foot antennas differ by less than one decibel.

Further Reading

For further reading, see the articles suggested in the text by hyperlinks.

Copyright © 2015 by James W. Hebert. Unauthorized reproduction prohibited!

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