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1566I found this interesting so I'm sharing it : Digital Selective Calling

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  • Bill Scanlon
    Oct 14, 2006
    • 0 Attachment
      Digital Selective Calling
      By Morton Biback,
      Registered Examiner, Marine Radio
      Chair, Electronic Navigation,
      Canadian Power & Sail Squadrons
      Searoom Logo
      | Home |
      If you look at a new marine radio, you will notice a red button marked “DISTRESS” protected by a spring- loaded cover to prevent it from being accidentally pressed. This button tells you that the radio has DSC, (Digital Selective Calling). DSC is an advanced, computerized form of VHF and MF radio designed for marine use. New radios with DSC capability are replacing the VHF and the MF type of radios that have been in use for more than half a century. They have all of the capabilities of the earlier radios and a number of new features that can add dramatically to the safety aspects and the usefulness of marine communications.
      DSC automates many aspects of radio communication. Without using a microphone, a user can make a distress call just by pressing one button on the radio. DSC will then automatically supply the Coast Guard (Canadian or US) and other vessels in the area with your identification and your location. You can even dial in the reason for the distress call. DSC will automatically repeat the distress call until it is acknowledged. These digital communications result in visual messages being displayed on a receiver’s display screen much like information displayed on a computer's monitor.
      DSC radio can make distress calls, urgency calls, safety and all ships calls as well as routine calls (the usual person to person type calls we make using non-DSC radios) using only buttons on the radio's keyboard. They can also digitally make position requests (asking other vessels their exact location) and polling calls (who is within communication range?).
      In the same way that your telephone rings when you receive incoming calls an alert will sound if there is a call for you or if there is a priority call such as a distress, urgency or safety message. Eventually, there will be no need to monitor Channel 16. In Canada, the requirement that compulsorily fitted vessels monitor Channel 16 has been dropped. Such vessels are now only required to monitor digital data on Channel 70 and MF frequency 2178.5 kHz. However, a large number of vessels are still not equipped with DSC radio, so it is desirable that Channel 16 still be monitored. The Coast Guards in both Canada and the US are still monitoring Channel 16 and will do so for the foreseeable future.
      If you make a digital call of any kind using DSC, your radio transmits the message on Channel 70; thus relieving congestion on Channel 16. This digital call is sent at ‘computer speed’, taking only a moment of air time.
      All DSC equipped marine radios can be connected to a GPS, so your radio ‘knows’ your exact location and the exact time and sends out this information with a distress call. This can truly be a lifesaver, it takes the "search" out of search and rescue.
      DSC calls can be made directly to another vessel without broadcasting; it is much more private, like making a phone call. Remember, a DSC call does not use Channel 16. If the call is directed to an individual station, then that signal is sent on Channel 70 and only that station receives the call. The call can include the channel number on which you want to hold an ordinary conversation. Channel 70 is only used for digital communication; you cannot use voice on that channel.
      You can store numbers that connect you to other vessels (like storing phone numbers on a cell phone). Your radio can keep a log of calls.
      DSC radios are available in four categories, Class A, Class B, Class D and SC-101. They differ in their features and cost.
      Class A and Class B radios are designed for commercial vessels. They are pricey and are not usually of interest to pleasurecraft owners.
      Class D radios are designed for commercial boats that are not required to carry Class A or Class B equipment and for recreational boaters. They are not as expensive as Class A or B. At the time of writing, prices for a Class D radio can be as low as $400. Most models cost about $500 to $1000. If the price of a Class D radio is within your budget, we recommend that you use this type of DSC radio.
      SC-101 is the low cost, entry level standard for DSC radios. By International law, it cannot be used on commercial vessels, but may be used on recreational boats. This class of DSC radio is very limited in capability. These can cost as little as $200.
      What do you get for your money?

      One difference between lower cost radios is the methods used to enter data. Better radios tend to have a keyboard method of inputting information rather than turning dials. There is one very important difference between a SC-101 radio and a Class D. A true Class D radio has two receivers, one of which constantly monitors Channel 70. An SC-101 radio has only one receiver. If you are tuned to a different channel or if you are transmitting, then the single receiver cannot receive on Channel 70. Some units have a quick change feature in which they momentarily listen to Channel 70 then return to the channel you are tuned to. This is still not as good a system as having dual receivers built in, one always listening to Channel 70.
      A Class D unit will not miss any calls arriving on Channel 70 because it constantly monitors that channel. Like anything else, you get what you pay for.
      VHF-DSC has the same range as ordinary VHF as well as the same power restrictions, but it is more efficient than ordinary VHF.
      MMSI #
      • Every telephone needs a phone number so that it can be called. This phone number identifies your phone and is unique. The same principle applies to DSC radios; each must have its own number. This number is called the Maritime Mobile Service Identity number (MMSI).
      • The MMSI number is nine digits long. The first three digits are the country identifier followed by another six digits which are unique to your marine radio. United States country identifiers are 303, 338, 366, 367, 368 or 369. The Canadian country identifier is 316.
      • Coast Guard Stations begin with a double zero. So a number like 003161234 would be interpreted as follows. . . The double zero would mean that this is a Coast Guard Station. The 316 indicates that it is a Canadian station. The 1234 further identifies that individual station.
      • Fleet numbers (see below) begin with a single zero.
      Obtaining an MMSI #
      • MMSI numbers are issued free of charge. In the United States you apply for one by filling out Form 605 which is available online at http://www.fcc.gov/formpage.html. You may also apply at BoatUS at http://www.boatus.com/mmsi/. SeaTow can also issue an MMSI number, apply at http://seatow.com/.
      • Canadians obtain their free MMSI number by contacting Industry Canada at http://sd.ic.gc.ca.
      Fleet Numbers
      • You may belong to a ‘fleet’ and share that fleet’s identification number. You may belong to a Yacht Club and all members of that club can be part of the same ‘fleet’. A call addressed to that fleet’s identification number will be picked up by all members of that fleet. . For example, the Canadian Power & Sail Squadrons has been assigned the fleet number 031600018. Even though a station may use a fleet number, it must also have its own MMSI number.
      Some Features to Consider when buying a DSC
      • If you want to have a fleet number as well as your own assigned station MMSI number, make sure that the radio you are buying can accommodate both numbers. Not all radios have this capability.
      • Some DSC radios require that you select the working channel manually once you have made contact on Channel 70. Others will automatically switch to the indicated working channel.
      • DSC radios can usually store MMSI numbers in much the same way that a cellular phone does. Some allow you to show boat names, etc. and these names appear on the DSC radio's screen when receiving a call from a station whose MMSI number is stored in your radio's memory.
      • If you need to be guaranteed that conversations are kept private, you can get a model that has a built in scrambler.
      The Simulator
      The Canadian Power & Sail Squadrons offer a Maritime Radio course as all operators are required to have a Restricted Operator’s Certificate (Maritime). Once you obtain this, it is good for life. As part of the course material, there is a CD on which there is a Simulator which you may use on your home computer. This simulator teaches the use of the different features of a VHF-DSC. It even has a simulated cruise that demonstrates the use of DSC. This CD is scheduled for release in March/2006.
      To get more information on obtaining your operator’s certificate, contact the Canadian Power & Sail Squadrons phone: 1-888-CPS-BOAT (277-2628)

      Bill Scanlon
      USCG Master 50 GT Inland Waters
      Towing & Sailing Endorsements
      Lic. # 1092926
      1984 Catalina 30
      Std. Rig  Hull#  3688
      Winthrop (Mass.) Yacht Club
      Navigare necesse est, vivere non est necesse

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