What is VHF?
- Mon, 4 Feb 2013
The most popular method of communicating with other boats is via very high frequency (VHF) radio. Learn how VHF works, the basics behind the frequencies you see on your VHF and understand the differences in locations.
In technical terms VHF is similar to the way that commercial radio stations (BBC Radio 1, Classic FM and so on) transmit. It has the advantage that equipment is relatively simple, and can therefore be compact and low cost.
To ensure that maritime users do not cause interference for other radio users, a part of the radio spectrum has been allocated specifically to this group and to make operation as simple as possible frequencies have been put into numbered channels. For example, Channel 16 (usually abbreviated Ch16) actually refers to a frequency of 156.800MHz, although you rarely need to know that. Because radio does not recognise geographic or political boundaries, and to ensure that boats travelling on international voyages can always communicate, the VHF marine band is the same all around the world.
There are 55 international marine channels, a similar number of private channels (allocated on a local basis to commercial organisations) and some other unique national channels. The USA and Canada employ a slightly different application of marine channels, using the same frequency but allocating more simplex rather than duplex channels. National channels include WX (weather) channels in the US, fishing channels in Norway and the marina channels M and M2 in the UK. To make sure that your radio is fitted with the correct local channels, be sure to purchase type-approved equipment in the country of intended use.
Range: How far will your VHF work?
Many customers ask us about the range (distance) over which a radio can communicate and it is the most popular question, with the hardest answer. Radio travels as waves, similar to light. Like light it can be reflected, reduced or even stopped by other objects. A popular response to the range question is ‘if you can see it you can talk to it' (known as line-of-sight) and this is generally a good guide.
Remember however that the radio signal comes from the radio aerial (not the radio itself) and therefore using a higher antenna allows the radio to ‘see' further. The same rules apply for receiving a signal, although of course base station aerials are mounted on very high masts and have much higher power, which is another influencing factor. A stronger, more powerful light can be seen further and more clearly and the same applies to radio.
Power is measured in Watts (abbreviated ‘W')and the higher the power the further the range, but it's not quite that simple. Even a very low power can give some range. Power can be used to improve the quality of signal and to overcome some obstacles. Remember though, more power out means more power in so shorter battery life for handhelds or non-recharging batteries.
Always start with the lowest power setting and work up. All fixed sets have at least two power settings, 1W and 25W. Handhelds have various power levels, Icom's being typically 2.5W to 5W as standard, with 6W from an optional battery.
Because VHF travels in straight lines, like light, as you travel away from land the curvature of the Earth prevents the signal from reaching you. This happens between 35-50 miles offshore. If you still need to communicate beyond those distances you need to look for some other way of doing it.