Spotlight on VHF: snazzy updates to a time-honored communications device.
Recently, I helped an acquaintance install a new 25-watt, fixed-mount VHF radio on his 22-foot center console. My friend plans to spend a lot of time on the rips out beyond 12 miles. On early forays, he quickly discovered the limitations of handheld VHF at that range--not to mention the absence of cellular service out there. (Little spooky, isn't it, when the shoreline disappears and you see the words "No Service.")
Height Makes Might
Basically, VHF communication operates on line-of-sight, station to station, radiating energy from one antenna to the next. Sources disagree, a little, on how that translates into range. Shakespeare, builder of marine recreational VHF antennas, advises multiplying the square root of the antenna height, in feet, by 1.42. Add the results for both parties, transmitter and receiver, for a general idea of total range.
Doing so, we find that two boaters using handheld VHF, each 6 feet above sea level, can expect about 7 miles of range. Two using fixed-mount VHF mated to an 8-foot antenna, mounted on a T-top (effectively 16 feet above sea level) should get about 12 miles. Again, just estimates. Atmospheric conditions, corrosion and other variables come into play. Curiously, higher output power has only a nominal impact on range, but can improve transmission quality.
According to the U.S. Coast Guard, in time of need, mariners with a VHF antenna 6 feet above sea level can expect at least 20 miles of service to a Coast Guard listening station, and often farther (charts of coverage for Florida may be found at www.navcen. uscg.gov). Outside of this safety net--and for general, non-urgent vessel-to-vessel-communications--the prudent mariner takes what steps he can, lawfully, to improve VHF range.
One important advantage VHF maintains over cellular service is that communications over a VHF channel aren't limited to single station to single station, as with telephones. Way out on the blue water, if a Mayday call on Channel 16 isn't picked up by authorities, it may at least reach another vessel within range. Nevertheless, an Emergency Position-Indicating Radio Beacon, or EPIRB, should be considered a must-have on any vessel traveling beyond 20 miles from shore.
The radio my friend selected, a Standard Horizon GX1700, is packed with features that would've been alien to mariners 10 or 20 years ago. (Retail price: $230 range. For details, www.standardhorizon.com.)
Like most marine VHF sets of recent build, this one is capable of Digital Selective Calling, or DSC. Basically, this is a digital transmission over VHF Channel 70. The radio includes a Distress button, which automatically sends out a distress alert to the Coast Guard and other DSC-VHF equipped vessels. Among other data, the alert contains your vessel's Maritime Mobile Service Identity. (Register for a free MMSI at www. boatus.com/mmsi or www.seatow.com).
Advanced Coast Guard direction-finding equipment can triangulate your vessel's position based on bearings to an analog VHF transmission on Channel 16. Better yet, if your VHF is linked to a GPS, the DSC distress message will include your latitude and longitude. You're pinpointed.
The DSC feature has general communications, benefits, too, such as hailing or locating a buddy by entering his MMSI.
One cool thing about the GX1700 is that it has a built-in GPS. Other VHF radios must be connected via NMEA cables to a GPS. Normally that's easy to do, but it can be tricky if you're routing things through pipework or rigging in tight spaces.
A secondary advantage of the internal GPS on the GX1700 is that the unit may serve as a standalone, backup navigation device. It can display vessel speed and course, as well as bearing and distance to one of up to 100 waypoints. In the unlikely event that the primary GPS fails, this VHF can call home and take you home.
A Better Antenna Mount
For a device whose primary purpose is marine safety, isn't it a little ironic that VHF antenna mount systems create hazards of their own? T-top mounts, for instance, commonly require a crewman to stand on the gunnel in order to reach the handle.
We don't even do that for outriggers anymore.
This year at the Miami Boat Show, TACO Metals introduced the Grand Slam 880, which allows you to raise and lower a VHF antenna from under the top. It's a brushed anodized aluminum body with Delrin roller bearing, compatible with 1-inch by 14-thread antennas. The stainless steel crank handle folds out of the way when not in use. We bolted one of these on my friend's T-top--which conveniently had been pre-rigged to accommodate TACO outrigger bases, the same bore as the GS880. Suggested retail price is $280.
Tigress, another marine fabricator, also makes a manually adjustable antenna mount for T-tops and hard tops, with a 3-inch mounting hole.
Some Other Trends in VHF
* Wireless Remote Handsets
Simrad's HS35 Wireless Handset (MSRP $169) is a cool wrinkle in the old-twirly-cable microphone mode. This waterproof transceiver enables the skipper to walk freely around on the boat (or tower) and use all the features of the "house" system, a Simrad RS35VHF/AIS combo ($399) which may be installed inside the console. See www.simrad-yachting.com
* What's That About AIS?
If you're fishing in the shipping lanes, having an Automatic Identification System (AIS) receiver is like having a very intelligent radar: You'll be informed as to the position, heading, speed and callsign of commercial vessels and others in the area equipped with AIS transponders. The new ICoM M506-series VHF radios, for instance, feature an integrated AIS receiver. This cuts the price, install and footprint of the black-box AIS units commonly used in network systems. The 506 has a huge display, compared to other VHF sets, at 132 by 96 pixels. Pretty neat.See www.icomamerica.com.
Jeff Weakley, Editor
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|Title Annotation:||FS SEMINAR: ELECTRONICS|
|Date:||May 1, 2014|
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