By Frank Lanier
VHF communications are an integral part of any safe, enjoyable day on the water.
Hand-held VHF radios are popular choice with boaters due to convenience
and portability (a handy option for small boat or dingy use), however with a
maximum output of six watts range for even the best hand-held is limited to
around five miles. Compared to the
25 watts and approximately 25 miles a fixed mount unit provides, the choice is
clear as to which you’ll want for primary communications should the feces hit
the rotary oscillator.
a fixed mount VHF radio is fairly straightforward and well within the ability of
most do-it yourselfers, however if you have doubts concerning an installation,
always seek the advice of a competent electronics technician.
first step is selecting a VHF radio and antenna that meets you needs.
There are numerous choices available when it comes to radios – the best
approach is to list the models that offer the features and price you want, then
narrow it down from there. Factors
to consider when selecting a radio range from location (waterproof models or
those with remote mikes for exposed installations for example) to the unit’s
warranty, which can range from one year to three or more.
selection is one of those areas where you really do get what you pay for.
Regardless the VHF radio selected, performance will only be as good as
the antenna you pair it with. Considerations
for purchasing a VHF antenna include price, construction (type and size of the
element, quality of components, finish, etc), and the antenna’s gain, which
we’ll discuss in a moment. Less
expensive fiberglass models often utilize thin copper wire for the “element”
(the part that actually radiates and receives signals) rather than the more
substantial brass or copper tubes found in higher end antennas.
The nylon ferrule (mounting base) of lower end antennas are also more
prone to failure than the chromed brass ones found in better quality units.
to material selection wire antennas provide less windage (making them ideal for
sailboat masts) but are “whippy” in longer lengths.
Fiberglass antennas are more beefy and ridged, meaning they can be made
longer without excessive movement, providing both height and strength for deck
end antennas also typically utilize better coax, the cable that conducts the
signal from your radio to your antenna – some antennas come with a length of
coax cable (which may or may not be long enough), while others provide a short
lead and require purchase of additional cable, connectors, etc.
As with any wire run the primary concern here is signal loss, a factor of
both cable length, quality of construction, and the number of connectors or
cable slices in the run (each of which increases signal loss).
are three common types of coax: RG-58 (the least expensive), RG-8X and RG-8U
(the best, providing the least amount of signal loss).
Signal loss for cable runs on smaller vessels (typically less than 20
feet) is not generally a huge concern, however even in such a short run signal
loss can be double when using RG-58 vice RG-8U.
critical element of antenna selection is gain,
the increase (or decrease) of an antenna’s effective radiated power.
Gain essentially describes how an antenna amplifies and shapes (or
refocuses) the signal it transmits, channeling more of it towards the horizon
for example (where it does the most good) rather than skyward or into the water.
Gain is measured in decibels (dBs) and VHF antennas typically fall within
three common ratings: 3dB, 6dB, and 9dB. In
a nutshell, antennas with a higher dB rating provides a sharper, more
concentrated radiation pattern (and greater theoretical distance) than those
with lower dB ratings (think spotlight as compared to a floodlight).
That being said, the best choice is not always simply to select the antenna with the highest dB. In the case of a sailboat mast installation for example, the more focused “beam” of a 9dB antenna will often be shooting skyward or down into the water as the vessel pitches and rolls, in which case the broader pattern of a 3dB antenna will give better performance. The best choice for a smaller power boat is typically a 6dB antenna, which provides maximum range with minimal signal loss (due to rolling while underway). Larger power vessels with dual VHF radios may opt for the belt and suspenders approach by installing a 9dB antenna at the upper helm (which will typically be used in calmer seas) and a 6 or 3 dB antenna at the lower helm for rougher conditions.
combination antennas (VHF/cell phone or VHF/AM/FM for example) are
available for installations where you have limited mounting area.
The cost however, is reduced performance on the VHF side - dedicated
antennas provide better performance and should always be the first choice if
space is available. Regardless the
type of antenna you choose, keep in mind VHF is “line of sight,” meaning it
should be mounted as high as possible for best performance,
Before you fire up that
drill or hole saw
beginning any project, take a moment to step back and visualize the installation
as a whole. Draw out the entire
installation and mentally walk though it in efforts to head off any potential
problems. You’ve chosen a
location for the radio, but is there a path to run power and antenna wires?
Can you actually access the mounting nuts and bolts for the antenna
mount? Hopefully you’ve verified
you can prior to drilling.
Doing the deed
Once you’ve chosen a VHF radio, selected an antenna, planned out the
installation, and assembled all of the necessary tools and required installation
items (wiring, connectors, etc) it’s time to get down to business.
Here’s some guidance and tips to help you along.
It’s not all inclusive and won’t cover every circumstance, but it
will help you along the path to VHF installation nirvana.
with the antenna and power leads properly connected turn the radio on and test
your installation to confirm all is well. If
you can listen to the WX station or hear the chatter of other VHF users,
you’re half way there, however you’ll want to conduct a radio check to
confirm both transmit and receive is working – a good practice anytime
you’re preparing to get underway.