An understanding of radio, and the ability to transmit and receive information on marine and/or ham radio frequencies, is an essential safety feature on a cruising sailboat.
This web page contains hints that we found useful as we attempted to unravel and master the mysteries of marine radio. These were accumulated as we studied a variety of sources, and from observation and experience. When we moved aboard, we knew how to use an AM-FM radio and the VHF. The need to get weather information when far from land, and the desire to have on-board e-mail capability forced us to grapple with purchase, installation, and use of a Single Side Band (SSB) radio.
On purchasing and installing an SSB, we began to study for the exams to become amateur ("ham") radio operators. This involved passing, first, the Technician Class exam, then a 5 words per minute Morse Code test, and then the General Class exam.
VHF-FM (Very High Frequency-Frequence Modulated) radio is cheap and used in coastal navigation. VHF is considered 30-300 MHz (marine band and DGPS). Channels: 16, 22 are Coastguard. 9 is recreational vessel to commercial shore. 67, 72 are between recreational and commercial vessels. VHF-FM frequencies are 156/157 MHz which is above normal FM radio. 68, 69, 71, 72, and 78 are for recreational users. 6, 13, 67 are for safety and navigation. DGMS is on 70 (digital use only). Marine operators are on channels 24-28 and 84-88. Note that the use of channels must relate to the needs of boat.VHF is line-of-sight communication and therefore depends on the height of your antenna and obstructions. 20-40 miles is about average.
HF (High Frequency or "Shortwave") radio is for high seas and coastal marine purposes. HF (the marine band, called ITU channels) are at 3-30 MHz and produce long-range wave propagation. Users must know which frequencies are available with sufficient range. HF radio can travel thousands of miles. Range is affected by transmitter power, antenna gain, but most importantly by atmospheric conditions. Channels (frequencies) must be selected to transmit on according to time of year and time of day and how far you want to transmit. Most SSB manuals contain a complete list of the ITU channels, and should identify high seas telephone channels.
The HF band includes marine frequencies and also includes frequencies allocated to the amateur service. On the SSB the user can program these frequencies into a set of User Channels. To use the reserved amateur frequencies the user must have an Amateur Radio License.
Use of the radio is strictly controlled by the FCC, and there are licensing requirements both for the user and for the station.
MF (Medium Frequency) is 2-3 MHz and has range of 75-150 miles during the day. MF radiotelephones are SSBs. Some SSBs can receive Weatherfax, Navtex, or Sitor broadcasts.
An emergency antenna for the SSB should be 23' long.
Commercial AM radio transmits quite a long way (several thousand miles at night) and you can sometimes pick up weather info here. Also, if you have a cheap AM radio you can use it as a direction finder.
The use of amateur radio (ham) equipment at sea is called Maritime Mobile (MM).
To use a computer with a radio, you must connect the SSB and computer using a "Terminal Node Connector" (radio modem) and have appropriate software.
To spell out words on the radio, for each letter use the internationally recognized system: Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliet, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whisky, X-ray, Yankee, Zulu.
Satellites have revolutionized marine communications. Traditional radio relied on ionospheric reflection and propagation. Geostationary satellites provide essentially line-of-sight transmission capability to most of the earth’s surface. They can transmit general info to all ships, or they can relay traffic to a specific vessel or shore station. The IMO (International Marine Organization) organized INMARSAT (the International Maritime Satellite Organization) to coordinate and regulate satellite use. INMARSAT has one member from each country. US is represented by Comsat. INMARSAT was incorporated in 1998 into SOLAS (the International Convention for Safety Of Life At Sea.)
As part of INMARSAT, ships now transmit weather information to government agencies, vastly improving the amount of data available to weather forecasters, and thus the forecasts.
GMDSS is the Global Marine Distress and Safety System, which is slowly going into effect worldwide.
Copyright 2005 The Trouser Rollers. All Rights Reserved.