- Code: help.vhf
What is VHF and how does it work?
The most popular method of communicating with other boats is via very high frequency (VHF) radio.
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. 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.
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.
Marine fixed units
For vessels with battery power, a fixed radio is usually a good choice. Several models are usually available with varying features, although the basic radio functions remain the same.
Units are traditionally designed to fit neatly in any cockpit or helm. Fixed radios do require installing and this will include connection to a power source and an antenna. When thinking about where to site your radio you should think about how it will be used.
You will probably need to use it whilst navigating, but may need to use it at the helm when entering or leaving port. Think carefully before installing. You will need to run power and aerial leads to the unit and be able to access all of its functions.
Handheld VHF radios work in exactly the same way as their fixed equivalents. Many of the features are shared and in Icom’s range they even follow the same operating protocol to help people who use both types.
There are advantages and disadvantages to handhelds.Advantages include small size and portability, usefulness in an emergency, independence from the vessel’s power and antenna. Disadvantages are related to the power output and battery life, which affects range and how long the equipment can be used. Handhelds are most suitable for small vessels without their own battery source, as emergency back-up to fixed radios or additional radios for crew and tenders.
How far will your VHF work?
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.
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.