Feature 5 | COMMUNICATIONS SYSTEMS
The antenna must be tuned to match the characteristics of the radio; fortunately, most systems these days are supplied with automatic antenna tuning. Not so many years ago, MF/HF onboard
often equated to the ubiquitous ‘green box’, so-called because the Danish company SP Radio, subsequently acquired by Thrane & Thrane, dominated the market with its green-coloured Sailor sets. T&T’s modern Sailor equivalents are smaller, lighter and easier to use than their predecessors. The Sailor range includes 150W, 250W and 500W (peak power) transmitters, with SSB receivers, variously type-approved for use in GMDSS sea areas 2, 3 and 4. One example, the Sailor T2031 400W SSB duplex RT system, would normally be partnered by an advanced R2022 receiver featuring both amplitude and frequency modulation (AM and FM).
Compact units A typical HF-SSB suitable for smaller vessels is Furuno’s NMEA award-winning FS1503EM, a rugged splash-proof 150W unit that, linked with a computer and modem via an RS232 port, provides e-mail capability. It can also enable full marine HF weather fax reception if Pactor II or Pactor II Pro, from modem specialist Special Communication Systems GmbH (SCS), is added. The radio, type approved by the Federal Communications Commission (FCC), is easy to use, purchasers being able to choose either rotary or touch-key frequency/channel selection. The system can automatically scan the operating waveband 1.8kHz to 27.5MHz for radio traffic. Single-button access to the international long-wave calling and distress frequency, 2182kHz, is provided. Up to 199 pre-programmed user channels are available. The set is compact, weighs 31lb (14.06kg) and is easily mounted. When operated from a 12Vdc supply, it draws about 2A on receive and up to 60A (30A with a 24Vdc supply) on transmit, so care must be taken to allow for the peak level when planning the installation. Each set is supplied with a computerised antenna coupler with a 10m control cable. An optional remote control permits operation from a remote location and provides functions including intercom,
50
At one time ships needed a full-time radio offi cer to handle wireless communications.
instant 2182kHz selection, squelch and transmitter high/low power selection. British company ICOM has a strong
MF/HF-SSB presence that includes the IC-M700, M710, M801 and M802 (DSC) ranges. The IC-M801, for example, can be accommodated in a limited space thanks to a two-part configuration comprising a main ‘black box’ that can be installed out of the way, and a separate control unit for mounting at the navigation station. This unit incorporates the display (LCD) and controls, the latter including transmit power selection (up to 125W), a DSC ‘panic’ button and a front-panel keypad permitting direct entry of
Other radios having more controls - auto notch filter, pass-band tuning, IF shift etc - are said to be more problematic as the controls have to be set precisely before HF e-mail can work. ICOM also offers its PCR1500/R1500
communication receivers for mariners requiring the benefits of HF reception without the ability to transmit.
frequency.
Transmitting in the MF/HF marine bands, the system has a 1200-channel capability, including some 1035 domestic and international pre-programmed channels, as well as up to 160 ‘favourite’ channels that can be programmed in by the ICOM dealer. Advanced digital signal processing is used, says the company, to eliminate noise and interference. A variant, the IC-M801E, has ITU Class E DSC. (Classes D and E are suitable for non-SOLAS vessels, while Classes A and B are required for SOLAS shipping.) The more powerful IC-M802 offers 150W peak power and 1195 channels. Used with a modem, the system likewise has e-mail capability and can memorise a user’s e-mail access frequency mode and bandwidth setting for one-touch access. Feedback from users suggests that the IC-M710 and IC-M802 sets work well with Pactor II modems to provide e-mail.
VHF Marine VHF is the most ubiquitous form of onboard radio, being present on virtually every craft that operates more than a few hundred metres offshore. Operating in the frequency band 156-174MHz, marine VHF offers reliable simplex (one way at a time) voice communication - to an extent data too as DSC comes in - although over a range that is limited by the heights of the transmitting and receiving antennas since VHF is basically line of sight. Range can extend as far as 50 miles (80.46km) or more when the higher power setting, 25W, is used with high-mounted antennas. Low-power (1W) transmission is used for close-range communication. VHF transceivers operate on standard
international frequencies or ‘channels’. For example, Channel 16 is the international calling and distress channel, Channel 80 is often used by marinas (UK) and Channel 67 is used by the UK Coastguard. Modern equipments also have Channel 70, reserved for digital selective calling (DSC), the GMDSS system that can send out a distress signal giving vessel identity and position (if there is a GPS input to
Ship & Boat International November/December 2008
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