Radio Check

High Performance VHFs

FSF Staff February 2, 2012

Essential for recreational and commercial boaters, two-way VHF radios provide reliable communications in addition to 24-hour Coast Guard monitoring for emergency situations. They also offer marine weather reports with wind and sea conditions, user-friendly attributes and recently implemented AIS and DSC capabilities. With advancing technologies, VHF radios remain one of the most important pieces of safety equipment on any vessel.

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VHF transmission distance is directly related to antenna height. Photo: doughertyphotos.com

Even though we rely on Very High Frequency radios for essential on the water communication, most don’t put too much thought into the matter. However, it is important you have a firm understanding of what can influence VHF performance. Because VHF radios work by line of sight their range is limited by antenna height. Most boaters believe that power output is the only influential factor in determining effective range, but this is simply not the case. While a 25-watt fixed mount radio certainly provides greater power and range than a 6-watt handheld, it’s all about the antenna.

While AIS is still rather unfamiliar to recreational boaters, it has been relied upon in the commercial and government sector for years.

The newest and most advanced VHF radio matched with a low quality antenna and poor installation will result in lousy performance, while the highest quality antenna will bring a middle of the road VHF up to par. Although there’s a formula that can be used to calculate your radio’s theoretical range, you must also take into consideration the height and quality of antenna on the receiving end.

Like everything else in the marine industry, you typically get what you pay for. And when it comes to VHF antenna length, size does matter. The construction of an antenna and the wrapping of the fiberglass are also determining factors in price and performance. You’ll also need to select an antenna with a gain rating that’s matched to your radio and application. With VHF radios limited by the FCC to a maximum of 25-watts, antennas can’t increase power, but they can direct signals in a more concentrated beam for what is perceived as an increase in output. The efficiency of an antenna’s ability to transmit a VHF signal is referred to as gain and measured in decibels (dB). Common gain categories are 3dB, 6dB and 9dB.

In addition to selecting the proper antenna, installations utilizing less than perfect connections and improper coaxial cable will greatly hinder a radio’s overall performance and range. With that being said, 25-watt fixed units offer an approximate rang of 25-miles, while 6-watt handhelds cover around 5-miles.

VHF marine radios have been relied upon for years, but forward-thinking manufacturers have recently developed some extremely beneficial features and attributes. The latest innovations for recreational users include Digital Selective Calling (DSC) and Automatic Identification System (AIS) compatibility.

Several VHF radios provide Category D Digital Selective Calling modes, but not all VHF marine radios have the ability to send and receive DSC data. With this function one can request the position of another vessel, or simply send your position to the vessel of your choice. Furthermore, with the push of a button a distress signal is automatically broadcast to all DSC equipped vessels and command centers within range. This transmission will include your identity, position, and nature of distress.

Building on the features of DSC, marine radios have started to incorporate AIS. Vessels equipped with AIS transmit and receive information such as vessel position, status, speed and course, as well as the name, length and draft. While AIS is still rather unfamiliar to recreational boaters, it has been relied upon in the commercial and government sector for years. It seems as no surprise why it would benefit the Coast Guard to identify a vessel and learn its course and speed in real-time, but it is also a huge help for search and rescue crews as they can learn the precise position of ships in distress. AIS also identifies radio beacons and other navigational aids for increased situational awareness.

Standard Horizon’s Matrix AIS+ receiver has a dual channel AIS receiver built-in and graphically displays AIS target information including call sign, ship name, bearing, distance and more. A Closest Point of Approach (CPA) Alarm lets you know when an AIS equipped vessel may be approaching too close to your location and a GPS interface can display AIS information on compatible units. You can see your 10 closest targets and display their vessel info, distance, bearing, speed over ground, coarse over ground and heading. If you want to hail them on the radio simply hit the direct call button and select a channel. Communicating on the water has never been easier.

When it comes to selecting the proper VHF radio for your particular application—DSC and AIS equipped or not—the options are numerous with hundreds of models available. Do some research and be sure to select the proper unit for your particular application. If you are simply interested in no-nonsense performance for short-range communication a simple handheld unit will suffice. If you’re more inclined to head over the horizon there are some pretty crafty features available with modern fixed mount VHFs.

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