Types of VHF sets:
Non-DSC VHF sets on yachts and motorboats will still continue to work, will still be legal to use and certificate holders do not need to do a conversion course until they choose to upgrade. After 2005 Coastguards will cease to monitor Channel 16 in the way that they do now, that is with a dedicated officer on headset watch 24 hours a day, but they will continue to have a loudspeaker watch on channel 16 in the operations room. Increasingly the boat without VHF DSC radio will be at a disadvantage.
A transportable set is an invaluable second radio for use in an emergency when it can be taken into a life raft or used on deck to communicate in a rescue situation. It is useful for safety reasons in a tender when going ashore or in a safety boat when organising dinghy sailing events. A portable set is a good buy for non-boat owners who charter or who go afloat occasionally. They have a limited range but do require licensing and certification. Portable sets with a very limited DSC facility are available. They are intended as an addition to a full VHF DSC set, not as a substitute. Note that the portable set covered by a ship’s radio licence can only be used on the vessel covered by the licence or by its tender(s). It is illegal to use the portable ashore.
VHF DSC radio sets
From 2001 all new non-portable radios sold must be VHF-DSC or be capable of being converted to DSC by the addition of an extra ‘black box’. These are called DSC Controllers. It will provide the digital selective calling (DSC) facility which is the special feature of the new type of set. What this does is to send, on channel 70, a burst of digital signals in a code to ‘call up’ another DSC set. This call can be directed at an individual, using their MMSI, a group of boats or ‘all stations’ in an emergency. Once the link has been established by the digital ‘call’, normal voice transmission will be used. The DSC is essentially a new method of establishing communications, more reliably than was possible before. The digital signals are of high radio quality and rapid, the alert taking just 0.5 seconds. It can be used in both routine and distress situations.
There are different classes of controller with varying levels of capability for use in different types of vessel.
The Class D controller is the one designed for use with VHF on yachts and motorboats who make passages within VHF range of the coast. Fitting one of these is not compulsory on private boats. On small boats used at sea commercially, sea school boats for example, it may become a requirement. This will be to the great advantage of their students who will be able to see the sets in use and appreciate their advantages.
Other controllers for VHF DSC are available to meet the requirements of ships. These include Class A and B Controllers, which have enhanced capabilities.
What is the range of the set?
Those sailing across an ocean, or even the Bay of Biscay, need radios that transmit over vast distances. Licensing arrangements are different too.
The range of transmission of VHF radio telephones is limited by a number of factors. The height of the aerial is very significant as the propagation of the radio waves is only slightly more than ‘line of sight’. This includes the aerial height of both the transmitting and the receiving station.
When talking from yacht to yacht expect a range of 10 to l5 miles with aerials fitted at the tops of the masts. Those commonly fitted to yachts are known as ‘unity gain’ aerials. They are made of thin wire and often have wind instruments attached. They are recommended because, although the range is not as good as the taller rigid aerials used on motorboats, they cope better with the heeling effect often experienced on yachts! The better range of a ‘high gain’ motor cruiser aerial is only achieved if it is mounted vertically.
It should be possible to talk to a Coastguard station from 30 to 40 miles offshore because of the height of their aerial.
Transmitting range is also affected by the transmitting power of the set. The maximum power allowed is 25 watts. There is also a low power setting, which reduces the transmitting power to 1 watt. This should be used for all short range routine communications. You might think that it is always a good idea to broadcast your signal as far as possible. This it not so. Remember that each channel can only be used for one transmission at a time. Powerful signals cause more inference to other radio users. If you are calling another craft nearby or a marina, use low power. Try to use low power for all routine communications. The use of low power does not change the receiving range of the set.
A portable VHF set has yet another type of aerial. This is flexible and will operate at a wider range of angles. The low aerial height and a maximum power output of 5 watts reduces the range of transmission of these sets. Between portable radios the range can be up to 5 miles, increasing to 10 miles to a Coastguard station, if there is no land in the way! Remember, with portable radios there is always the risk that the battery will go flat.
The information about ranges of transmissions is for average conditions and good circumstances. Ranges can be influenced by:
o Atmospheric conditions, especially high pressure, can increase the range and cause interference from distant stations.
o Land. Boats operating near land may have poor reception with signals being blocked by hills or buildings.
o Incorrect installation of the aerial, or damage to the coaxial cable connecting the aerial to the set, can give poor reception.
o The proximity of other electronic equipment can cause interference.
For these reasons it is best to have the fitting done, or at least checked, by a professional electronics engineer.
A portable radio has a range of 5 miles to another portable, 10 miles to a Coastguard Station.
All distress calls should be transmitted on high power.
Many yachts carry emergency VHF aerials in case of dismasting, which is a very good idea, but failure of the electrical supply is a more frequent problem! The emergency aerial has a plug attached to connect it to the back of the set. For maximum range, situate the aerial as high as possible, but realistically expect a greatly reduced range. When the mast is lost, many people are surprised to hear the radio apparently still working. This is because the co-axial cable is acting as an aerial over a short range, but transmitting without an aerial will damage the set permanently.
A portable radio could be useful under these circumstances!