The fixed VHF has a maximum power of 25 watts imposed by regulations which limits its range from 15 to 20 miles boat/boat and from 30 to 40 miles toward coastal stations. The new generation of VHF on the market, come equipped with the DSC (Digital Selective Calling) system, ASN (Appel Sélectif Numérique) in French.
Make the right choice
All VHF, fixed and portable are subject to regulation and certification. Therefore, in terms of standard functions and power they are all identical. What makes the difference is water proofing and additional functions such, as on the fixed, having the possibility of creating a network for communicating with other VHF on board (interphone,) or of having DSC and AIS outputs, for interfacing with a compatible card reader. On portables, there are small differences in terms of autonomy (capacity and type of battery,) encumbrance, waterproofing and buoyancy.
-A portable VHF can be taken with you in all situations, especially emergencies. It is a real safety feature. -If the battery does not provide more than a few hours autonomy, certain models come with battery support. It is easy to have them available and does not interrupt communications. -Portable VHF can meet differing standards of waterproofing; spray (IPX4,) to immersion (IPX8.) Even if one does not utilise the VHF underwater the seal will protect the circuitry from moisture. A VHF left on board for winter, will require an effective seal… -There are also waterproof cases which work well, in the dinghy for example. In addition to protecting the VHF they also provide a strap to fix it to oneself or the boat. -Attention, immersion proof does not mean unsinkable. Some models do possess this feature. In case of being dropped into the sea they will float, making their recovery possible.
-For a permanent interior installation (chart table,) or on an external console ( use a VHF with a waterproof face.) -In case of interior installation, use a remote loud speaker to hear from the external helm position. One may also choose a model that provides a remote, to use the VHF from a distance. This is a very useful function in case of man overboard situations, as one may remain in contact with the castaway and the rescuers. -A fixed VHF DSC must be connected to a GPS(to give the position in case of emergency.) It can also be connected to a card reader (or computer,) to view geographically, the distress position received (the position of the vessel that sent the message.) -On top of the range models, emphasis is placed on the quality of the connection and display. For intensive use, these models are recommended.
VHF installation and the antenna
The chart table is often selected as the location for a fixed VHF, except for sealed models which may be located to the exterior. In all cases, it is important that the connections to the rear of the unit remain accessible. The antenna must be located as high as possible, at the head of the mast for sailing vessels and on the wheelhouse for motor vessels. Avoid cable connections (connector at the foot of the mast,) between the antenna and the VHF, to avoid losses. Marine VHF, the frequencies comprised between 156 MHz and 162MHz, waves propagate in straight lines, like light beams. It is limited therefore, by obstructions: buildings, dams, cliffs, headlands, islands..And at best by the curvature of the earth, the direct signal will then be hidden by the horizon (there are, particular conditions which may permit propagation over the horizon, but these are however exceptional.) It is for this reason the antenna is installed as high as possible, in order to remove as many masking objects as possible. The calculation of the theoretical range, results from the simplified formula which gives an approximate value: D = 2.2 (Root (H1) + root (H2)) with H1 and H2 the height of the two antennas in metres, and D in nautical miles. Thus they have usually obtained between 2 and 10 nautical miles of range for a handheld VHF, and between 25 and 30 nautical miles for a fixed VHF with a remote antenna.
DSC: A worldwide safety system
This system was designed for commercial and fishing vessels with the goal of sending rapid safety messages. It has now also been adopted by leisure vessels. In an emergency press the DSC (red) button to send automatically, an emergency signal on channel 70. This message includes the boat identification (MMSI number,) position (if the VHF is connected to the GPS) and the nature of the emergency (selected from a preprogrammed list in the VHF.) This signal is received by CROSS and all boats equipped with VHF DSC, within range. In the minutes following the transmission, CROSS acknowledges the signal and then contacts the boat on channel 16. The VHF DSC, in event of call, switches automatically on 70 and returns to 16 when CROSS acknowledge reception. Out of range of coastal stations, if a DSC signal is sent, it is received by all vessels with VHF DSC capability within range. They may then act as relays to alert the rescue services. They can do this through VHF, if within range, or by other means of long distance communication (BLU satellite for instance.) In addition to safety, DSC permits connection to another vessel, provided the MMSI number is known. In this case, there is no need to select a channel number, one dials the MMSI number and the VHF selects a free channel. The correspondent (and only him/her) receives the call (ringing) with the on-screen coordinates of the caller. One may also, if the VHF has a Track-your-Buddy output and is connected to a compatible card reader, position on the screen boats to which it has memorised the MMSI number. Similarly, VHF which has a DSC output connected to a compatible reader, may display on the screen the position of a boat sending the message.
“DSC is very simple to use, do not misuse it and trigger false alarms. Train your crew to react correctly in case of emergency.”
Accessories for fixed VHF Antennas
If we have seen that the height of the antenna greatly affects the range of the VHF, their quality also plays an important role. For reception all models are capable, for transmission this is not the case. We offer you two models with gains of 3Db (antenna length 0.90 and 1.50m) and 6Db (antenna length 2.40m.) All models are fibreglass with a polyurethane covering. For a sailing vessel an antenna of 3dB is sufficient, if it is installed at the top of the mast. On a motor vessel, it is recommended one uses the 6dB model. For safety, an emergency antenna is strongly suggested. In case of problems with the principal antenna, see dismasting, it may be replaced rapidly. External loud speaker When the VHF is installed in the interior, its speaker is not sufficient for hearing calls from the cockpit. The solution is to equip it with a remote speaker. All models possess a jack for an external speaker. If it is installed in an exposed area, one must select a waterproof model. A switch to select hifi speakers exists. This avoids having to install supplementary speakers.
Portable VHF accessories
Covers for protection and support
If your VHF isn’t waterproof, do not hesitate to use a cover. Inside the boat to prevent it being placed on the chart table, from where it may fall, one should, ideally, use a fixed support (wood or acrylic.)
12volt charger or battery box
If you want to stay more than one day at sea, equip yourself with a 12 volt charger (certain brands provide them as standard.) If you can not find one, choose a 12/220 volt converter. The battery box, if it is adaptable, is a plus for safety. If this is not the case, it is prudent, for a journey of several days, to take additional batteries (remember to keep them charged!)