- Choosing the best marine VHF antenna and installing it correctly for optimal reception -
Choosing the right antenna and installing it correctly are essential for the proper functioning of an on-board VHF radio device, depending on the range and quality of communication. Depending on the manufacturer, antennas are made of stainless steel, fiberglass or are coated with elastic black rubber. To further improve reception, an amplifier can additionally be installed.
When installing a VHF antenna, a simple rule of thumb applies: the higher it is mounted, the greater the range. The VHF radio antenna is therefore always mounted at the top of the mast in sailing boats. You will also find the corresponding antenna mounts in our shop.
For sailboats, we recommend a VHF antenna with 3dB power gain. For motor boats, use as long an antenna as possible with a power gain of 6dB or 9dB. Many antennas can be mounted on foldable feet to reduce the overall height of the boat if necessary.
In principle, a marine radio system consists of three components, which, when combined and configured correctly guarantee the best results: the VHF radio device, the VHF antenna and a coaxial cable with connectors and plugs.
In addition to the VHF antenna, the cable has a very important function. The correct type of coaxial cable is crucial for the radio system, otherwise, the entire on-board network could itself become the antenna, which would result in noise and interference, making effective radio contact almost impossible.
When choosing the coaxial cable, pay attention to the characteristic impedance, which in radio systems is always 50 ohms, and to the attenuation of the cable, an indicator of how much energy is lost for each meter of cable. The attenuation is the same when sending and receiving - the thicker the cable, the better.
Two types of cable are common in the nautical sector: RG58U with an external diameter of about 5 millimeters for cables up to 11 metres long and RG213 with an external diameter of 10 millimetres for cables up to 50 metres long. It is important that the insulating material is resistant to sea water and UV rays. A tip: adapt the cable to the length needed for your boat, because every meter of coiled and not actually necessary cable reduces the reception performance.
- Reception on board -
A VHF boat antenna is basically a device for transmitting and receiving electromagnetic waves. Strictly speaking, an antenna is a conductive metal object that transmits and/or receives electromagnetic waves from radio frequencies. Thus, the antenna is the most important part of a radio connection, it is the interface between the transmitter or receiver and the radio wave signals. The task of the antenna is to absorb or emit electromagnetic waves in order to communicate or broadcast information.
Since VHF radio masts are not usually directly connected to the transmitter or receiver, it is important that the cables and connectors have been designed for the specific requirements of marine life, i.e. they must be resistant to sea water and UV rays. When assembling, keep in mind that every metre of cable and every connector or adapter attenuates the signal: the higher the gain of an antenna, the longer the antenna cable can be. The better the quality of the cable, the longer the cable can be.
For example, the ISAF rules for offshore racing prescribe a maximum attenuation value for 50 ohm coaxial cables. The rule is: the longer the coaxial cable, the greater the attenuation. According to the ISAF, a maximum power loss of 40% is still permitted, meaning that at least 15 watts of the original 25 watts of transmit power must go to the VHF antenna.
Ideally, the radio system should operate independently of other equipment on board. This means that it must have its own power supply with a suitable fuse. In addition to a permanently installed marine VHF antenna, an external antenna should be carried on board in case of emergencies, such as if a lightning strike damages the installed antenna.
A VHF antenna can be used for several devices at the same time for example, in addition to marine radio, it can also be used for radio and multimedia reception or AIS. However, an AIS antenna splitter is required for this.
If the marine radio is installed below deck on the navigation table, as is usual, radio messages in the cockpit are often difficult to understand. Some radios therefore have an optional second control unit for the helm station, or alternatively it is also possible to install an external loudspeaker.
Graham L. on 02.12.2023
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