Buying a VHF Unit

by admin

Nick Cohen takes a look at buying a VHF, aerials and provides a comprehensive list of VHF units available in New Zealand and Australia.

There are a couple of basic things to consider. Firstly, do you want a fixed unit or handheld? Secondly, just how much do you want to spend? With so many makes and models to choose from it is easy to base the decision on dollar values rather than performance values. Sure you may not be a super techno-whiz person so like most don’t have an understanding of things too technical and would rather go for something that is simple, straightforward and easy to use.

There are only a couple of points to remember, the first being that any VHF radio is only as good as the aerial attached to it. So when you are shopping for a VHF, you are also shopping for an antenna. In the case of handhelds, you have little choice, although most can now be linked up to fixed aerials as well to enhance their power.

As for most things, you only get what you pay for when buying a VHF and the cheaper units may not always have the receiver performance to match the higher priced units. One can forget about the transmitter performance for two good reasons. Firstly, the radios are limited to a 25-watt maximum output. Secondly, due to the nature of VHF communications, the rangeability of any comparable sets are least affected by the power out, but more affected by the aerial. As a rule of thumb remember…a cheap radio with an excellent antenna will outperform an expensive radio with a cheap antenna every time!

Splash or Water Resistant

If you decide on a handheld unit, you should check out whether it is ‘seriously’ waterproof or just water-resistant. Drop a fully waterproof unit in the water and the chances are it will still work, despite the dunking. Not the same can be said for one that is only water-resistant or splash-proof. There are, however, excellent plastic covers available for handhelds that will keep both salt spray and rain off your unit.

You will see from the listing that the grade of waterproofing differs and each designates their capability. The higher the final number, e.g., IPX7 or IPX8 means the unit is capable of withstanding the greater water ingress caused by splashing or immersion. It also pays to check on the operating time of the battery and what warranty period the manufacturer is offering. Size and weight also come into it, but they are all reasonably compact. Handhelds obviously can be stored anywhere or mounted in a dedicated mount that’s handy to get to when required. With a fixed unit, you have the choice of flush mounted, or bracket mounted.

Some models come with a flush mount kit already, as part of the unit design, while with others it is only available as an option. If you do go for a fixed unit, then consider where you are going to place it on the boat as generally they are only splash proof and don’t like to be liberally doused in salt water. There are some units however that the manufacturers promote as being totally waterproof that would be fine if you have to mount the VHF outside in an exposed area.

Cost, Coverage & Communication

The beauty of VHF can be summed up with the three “C’s” ..Cost, Coverage & Communication. The cost of operating a VHF is basically  free. There are no monthly rentals or on-going call charges. The only cost is the small annual licence fee, which is charged essentially to cover system maintenance. Equipment costs are low and you can get a good set, including an aerial, for under $300.

VHF coverage is what we call ‘line of sight’, which means that the radio waves don’t go around corners. However by locating a repeater in a prominent location that is visible from many places, it’s possible to get excellent coverage over a wide area even from a small handheld.

For communications ability, the VHF system at sea cannot be beaten. The very nature of the system, a limited number of channels spread over a wide area, means that calls are quite public and can literally be heard by anyone who cares to listen…..and that is both the system’s strength and weakness. If it’s privacy you want then the cellular phone is the way to go and with the coverage so good today around most of the popular recreational boating waters of New Zealand, they are certainly becoming the most popular system for personal communications.

Antenna Answers
As already mentioned, a VHF is only as good as its antenna. Nothing beats a good antenna system for giving you a powerful radio signal. Your marine VHF antenna and a lighthouse have something in common. Did you ever wonder why the light beam from a lighthouse is so bright? An optical lens concentrates ordinarily wasted vertical light waves back down to the horizon for a more powerful illumination.

In VHF antennas, we do the same thing by taking the normally wasted vertical component of our transmitted signal, and beaming it down, close to the horizon, where it will do the most work for our VHF transmitter and receiver.

Just like a Fresnel lens, a quality VHF antenna may intensify your transmitted signal many times beyond the actual rated power of your set.

Within the fibreglass tube are matched and stacked antenna elements, strategically placed end-to-end for maximum low-horizon gain. The more elements are stacked, the closer the signal will hug the horizon. This allows you to talk well beyond the expected range of your VHF set, and to hear and transmit signal further than everyone else around you with physically shorter antennas.

What dBi Gain Means
3 dBi = 2 times radio’s output power

6 dBi = 4 times radio’s output power

9 dBi = 8 times radio’s output power

(The subscript “i” refers to a reference theoretical isotropic (point source) antenna.)

Note: A 6 dBi antenna needs to be twice as long as a three dBi antenna.

Most metals will oxidise badly when exposed to salt spray, so this is why quality marine VHF antenna elements are encapsulated within a sturdy, yet flexible shaft called a radome. There is more inside a radome than just a little piece of wire. Carefully tuned elements are securely joined, end to end, to form a vertically stacked colinear array that is pulled into the radome and firmly positioned to prevent rattle and fatigue. These tuned elements are critically designed to provide the best possible radiation of a transmitted signal and the best capture of incoming signals.

The bottom of the radome is fitted with a mounting ferrule and an ample supply of top quality coaxial cable for routing to your VHF set. Also, VHF antenna systems operate without any further need for a ground. The ground plate is built into the antenna network, so everything is in one nice, neat fibreglass radome (tube). If you plan on buying an antenna, then for the best results go for the tallest that is practical for your boat. The higher the gain, the further you are going to communicate.

At sea level on most trailer boats, a 6 dB aerial is ideal, although a 3 dB unit is okay. A variety of ratchet and built-in ‘lift ‘n’ lay’ mounts and fixed mounts are available. Some of the smaller antennas are ideal for hand-held VHF sets and will dramatically increase their range. If you have a VHF hand-held, you can double its effective radiated power output by going to a 3 dB gain antenna.

I’ve Got An Antenna Question….
Q. Powerboat VHF antennas with 9 dB gain are reported “too high in gain” for boats in heavy seas. Is this correct?

A. A 9 dB gain antenna is suitable for a stable platform while 3 dB is best for smaller boats. However, on the water, generally a nine dB-gain antenna, even on steep rolls, is a better performer than other antennas with a broader pattern and less gain.

Q. Can I paint my antenna?

A. You sure can, but be sure to use paint without a lead base. Latex paint is a good way to go.

Q. I fractured my antenna, will it still work?

A. The lightweight antennas feature flexible coaxial cable top elements on the inside. Even though the fibreglass is fractured and folds all the way over, the coax inside usually stays intact. Just duct tape it back together until you can replace it.

Q. Should I cut off the extra coax I don’t need that is permanently attached to my VHF antenna system?

A. If it’s a VHF-only antenna, sure, cut the coax and solder on a new connector. Just make sure that you solder on the connector properly. Keep it as short as you like and don’t worry about cutting it at specific wavelengths. If it’s a combo VHF/CB, or the shortened CB antenna, leave the coax alone, it’s part of the antenna circuit. However, most cables are only 3-5m so it shouldn’t need cutting.

Q. What’s a simple way to test my connections to see if my VHF antenna system is working properly?

A.  Firstly don’t use an ohmmeter on the VHF lead in as some antennas have internal circuitry that makes the feedline and antenna and connector look ‘open’ or ‘shorted’. If you don’t have sophisticated meters, try this simple test.

1. Tune in a distant VHF weather transmitting station.

2. Disconnect the antenna plug, and the station should become very weak or disappear.

3. Insert just the tip of the coax plug into the radio socket, and the station should reappear, weakly.

4. Now, insert both the tip and shell in the back of the radio, and signal strength should increase slightly or significantly.

If this occurs, your antenna system is working properly. If when you slide on the outside shell, the signal completely disappears, chances are you have a bad solder connection at the connector, or although quite unlikely, something wrong within the VHF antenna.

New Technology
In recent years, VHF technology has been further improved to conform to international safety regulations and both commercial and leisure users have benefited from this.

GMDSS regulations have stipulated that handheld VHF radios are not only rugged and waterproof but that they are also simple to use and easy to operate, which has dramatically improved the design and build quality of handheld VHFs.

Today’s handheld VHFs have come a long way since the first units from many years ago. Special features such as flotation and strobe lights, GPS and noise cancelling are commonplace. The battery life is longer, the units are lighter and tougher and the ease of use so much better. Check out what you are buying and just how good the VHF unit is. If you are going to be using it in an exposed area, it is important to consider the waterproofing aspect. If you are going to mount it into your dash, then make sure you have enough depth to fit it. Same goes for a bracket mounted unit, especially if it is tucked in under the windscreen.

The very latest floatable, strobe and GPS packaged handheld VHFs are very different from the earliest VHFs that simply allowed you to call and receive calls. Even if you are not required by law to carry a VHF you should. Your mobile phone can only do so much and it is useless when wet.

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