While seemingly obsolete, VHF had a surge of pride. In the following virtual interview with this important boat accessory, you’ll discover everything you have never dared to ask.
Why is VHF the most popular tool for communication at sea?
The secret to the reliability of VHF radio on boats depends on the type of waves it uses to transmit messages. These are frequencies that allow clearer distance communication because they are less subject to interference from the atmosphere or from other waves in the ether.
The VHF radio uses metric, very high-frequency waves called VHF (Very High Frequency) between 156 and 174 Mhz, whose wavelength is approximately 2 metres. The size of its antenna, about half the wavelength itself, makes VHF communications ideally suited for all crafts, from large passenger ships to the smallest fishing boats or recreational yachts. But other types of waves are also adopted at sea, such as hettometric waves, medium frequency (MF), used for medium distance communications from vessels 100/200 miles from the coast, and decametric waves, high frequency (HF) used on the high seas, for example in oceanic navigation.
All models allow background noise to be filtered out via the squelch, which allows to set the sensitivity of the receiver. The power rating is indicated on the packaging of each radio. The maximum emission value allowed for recreational boating equipment is 25 watts, with the possibility of reducing it to just 1 watt to limit power consumption and to communicate at close range.
With the same transmitter power, the distance to which VHF communications can reach depends on the height at which the antennas involved are placed. For example, a range of 60 miles can only be determined between a boat and a coastal station, while between two boats the range is reduced to only 15 miles or even less if they are small boats. Beyond the transmitting power of the radio equipment, the discriminating factor is, above all, the earth’s curvature. The range, which in this case is defined as optical, will only be able to exceed the horizon line if the two antennas continue to see each other. VHF radio waves are less susceptible to interference and therefore the safest to use at sea. But pay attention to the antenna position above the geographical position in relation to the respective heights. In these cases, sailing boats are certainly advantaged by the possibility of installing the antenna at the masthead, bearing in mind, however, that it is only effective when operating vertically; when inclined it can lose up to 40% of its performance.
For some years now, the portable VHF has finally been able to replace the fixed station on board in Italy too. The portable radio on board is becoming increasingly useful: it makes it possible to make or receive calls while remaining at the helm, keep listening on 16 without having to go below deck, and take it with you for various eventualities, including the unfortunate transfer to the life raft when abandoning the vessel.
Portable radios are now increasingly inexpensive and morphologically similar to mobile phones. Although they can support most of the functions of fixed models they are subject to three fundamental drawbacks – a reduced emission power of only 5 watts (instead of 25), in order to limit the consumption of rechargeable batteries; a limited range due to the short length of the antenna; an operating range that depends on the type of batteries used and the opportunity to recharge them. For the correct use of a portable and, above all, legalised model, it is necessary for each device to be registered on the Operating Licence of the fixed apparatus on board, if any, or to have its own document, named after the vessel on which it is used or in the name of the user himself, who in turn must have the appropriate limited radiotelephone certificate.
To simplify the use of the equipment, it was agreed by international agreements to divide the frequencies of use into channels. Each therefore corresponds to a specific frequency, for example, channel 16 corresponds to 156.8 mHz.
What needs to be checked to choose a good VHF?
The basic characteristics of a radio concern the sensitivity of the receiver, i.e. the ability to pick up even weak signals, the transmission power to be heard more clearly, and the selective capacity, which allows it to stay on the frequency of the chosen channel without ‘overshooting’. Added to these are the operating range of the dirty signal filter, known as the squelch threshold, the power absorption (especially important in laptops) in both Hi and Low, in stand-by (lowest consumption) and in transmission (highest consumption). Then the physical details of the device count: size, weight and robustness, to which are added the readability of the screen, ease of use, ergonomics and the number of additional functions. The mix of these elements makes it possible to judge the last parameter, the purchase cost.
Are there any special requirements for speaking on the VHF?
The use of the VHF is under the full responsibility of the vessel’s captain. No one on board may take possession of it without his or her approval. The compulsory document required to operate the Vhf radio is the RTF certificate (Restricted Radiotelephone Operator’s Certificate for Ships), which is issued, without examination, by the Regional Inspectorates of the Ministry of Communications, and is valid on pleasure craft and ships of up to 150 gross tonnage and with radio stations of no more than 60 watts power.
What documents are needed to install a VHF on board?
Owners of equipment that complies with EC European directives (conformity is declared directly by the manufacturer) must apply for the appropriate Operating Licence by contacting the Harbour Office where the unit is registered, in order to also obtain the international call sign number, which is indispensable for jointly identifying the radio station and the vessel using it. On the other hand, owners of vessels or portable equipment will have to address their request directly to the Territorial Inspectorates of the Ministry of Economic Development, Communications Department, and will also obtain a personal code identifying the equipment and its owner.
DSC stands for Digital Selective Calling: basically, it is a function of the radio that allows emergency calls to be made on a frequency reserved for digital calls only, channel 70, where voice communications are forbidden and consequently traffic and interference are reduced, instead of channel 16. Should a distress call be necessary, for example, the DSC unit is able to automatically transmit a large amount of information within seconds to all units equipped with the same system in the navigation area, without having to wait for voice replies and without having to waste time repeating calls and details. The DSC distress message provides:
– the vessel’s MMSI, a specific identifier, making its specific characteristics immediately recognizable;
– the vessel’s position, provided by the interfaced GPS (if any) or entered manually;
– the UTC indicating the time when the last position was updated;
– the nature of the danger or damage occurred to the requester.
In addition to distress calls (Medé), emergency (Pan Pan), security (Securité) or ordinary (Routine) calls can also be transmitted (or received), which can then be continued in voice form. The voice and digital systems coexist and offer two joint and alternative opportunities to make communications. The DSC system belongs to the instruments adopted by the GMDSS, is associated with VHF, MF or HF communication equipment and is compulsorily present on every unit that carries out navigation for professional purposes.
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