Buying Tips from the Marine Electronics Journal
How to Buy Marine Electronics
For VHF Antennas Click Here
VHF stands for Very High Frequency. Because VHF signals travel in a
straight line and are not reflected back off the ionosphere as lower
frequency (HF or marine single sideband) signals are, the range of VHF
signals is limited to line of sight. Beyond the line of sight other vessels
pass behind the curve of the earth. Large buildings, mountains, and any
other obstructions that block the line of sight also affect marine VHF.
The range of VHF increases with the antenna’s height above sea
Fixed vs hand-held
Marine VHF radios are broken into two main categories—fixed
mount and handheld—and sub-categories also. For instance, handhelds
are available in waterproof and water-resistant models. Fixed-mount radios
offer the same waterproof and water-resistant sub-categories, and come
with or without DSC (Digital Selective Calling).
Whether handheld or fixed mount is better depends on your application.
Do you have a small boat or dingy without an electrical system? If so,
you’ll need a handheld radio, which operates on its own battery.
Even if you have a boat with its own electrical system and a fixed-mount
radio, it may be the handheld radio that saves your life. What happens
if the electrical system goes down? That handheld radio you keep on board
as a back up will be your only means of reliable communication.
On the other hand, any boat that goes any great distance offshore should
have a fixed-mount radio on board. The range of a fixed mount is 25-30
miles; a handheld is 7-10 miles maximum.
Waterproof vs water-resistant
Let’s talk about “waterproof” and “water-resistant” categories.
Even though there are different methods of rating marine electronics
for their “waterproofness,” the most widely used and accepted
standard is the J.I.S (Japan Industry Standard) rating. The J.I.S. ratings
go from J.I.S 0 to J.I.S 8. Don’t even think of purchasing a marine
radio without at least a J.I.S 4 rating. Let me explain. The J.I.S. 4
rating is “water-resistant,” which means the radio should
be able to be splashed from any direction and suffer no harmful effect.
Right now the highest rating you’ll see is J.I.S. 7, which specifies
that: “Water shall not enter the radio’s enclosure when it
is immersed in water under defined conditions.” The J.I.S. 7 rating
is the true “waterproof” rating. (Here’s a helpful
hint: After a long day of boating it’s a good idea to spray off
your marine radio—but only if it’s J.I.S 4 or better. This
will wash off any salt residue that may have adhered to the unit, and
will improve its longevity.)
Benefits of DSC
Since 1999 any newly designed marine VHF radio has to have DSC built
in. DSC is only one aspect of GMDSS (Global Maritime Distress and Safety
System), which was originally slated to be fully implemented for some
types of commercial ships by Feb. 1, 1999. In order to understand DSC,
it’s necessary to briefly explain GMDSS.
The main purpose of GMDSS is to provide an efficient system over a greater
range to enable search and rescue and nearby vessels to come to the assistance
of any vessel in trouble. The equipment requirements of the GMDSS system
are a fixed-mount VHF radio with DSC, fixed SSB radio with DSC, handheld
waterproof VHF radio, EPIRB, Navtex receiver, and Inmarsat.
DSC will be used to transmit and receive distress signals and to relay
emergency and safety calls and automatic alerts. This will be done automatically
by the touch of a button, which will free mariners from having to continuously
listen to Channel 16 or other distress channels. If a distress call is
transmitted, an alarm will be triggered on all stations within range.
Although designed for emergency use, DSC includes many helpful “everyday” features.
One is “individual ship” calls, where you can contact a specific
ship directly through DSC to provide information such as location. Your
radio needs to be connected to a GPS, and you must know the other vessel’s
MMSI number. Simply put an MMSI (Maritime Mobile Service Identity) number
is a unique identifier much like a phone number given to all registered
DSC users. You can also do “group” and “all ships” calls,
as well as position requests.
One feature to look for in a DSC radio is the amount of MMSI numbers
that can be kept in the MMSI phonebook. Many DSC radios on the market
don’t have much capacity. When purchasing a DSC radio with position
request make sure the automatic reply (if so equipped) can be turned
off. At times you may not want an annoying acquaintance to be able to
locate you. Also, look for large DSC controls that are easy to find,
read and activate.
What else to look for
Whether you’re in the market for a fixed mount or hand held, the
first question to ask a sales person is: “What type up chassis
does it have?” There are many VHF radios that are nothing more
than circuit boards in a plastic shell. These units are usually inexpensive
but need to be replaced frequently. You’re usually better off buying
a radio with a cast aluminum chassis. The chassis serves multiple functions.
First, it acts as a heat sink. Transmitting on a VHF radio produces a
great amount of heat. If the heat is not removed from the internal circuitry
it can greatly reduce the life expectancy of your radio. A chassis also
dissipates shock and vibration, which are known killers of electronics.
Without the aluminum chassis the circuit boards take a lot of unnecessary
Do you want a rotary knob for channel selection, or up/down push buttons?
Many boaters like the more expensive rotary knobs, simply because they’re
easy to find in rough seas and much faster to get to the channel needed.
What about a loud hailer? This feature allows you to broadcast your
voice to line handlers for easy docking or even to other vessels. The
loud hailer is a widely debated feature. My opinion is, never purchase
a marine VHF radio around a built-in hailer (although at times they’re
nice to have). Remember that you’re buying a VHF—one of the
most important pieces of safety equipment. Its ease of use and reliability
are the most important factors.
Will you want to add a remote station to your fixed-mount radio? Today
many fixed mounts allow you to add one or more remote stations that offer
full operation. This is extremely handy when you have a cabin, tuna tower
or fly bridge where you’d like to have a second station. Also,
most of these allow for intercom between stations.
Last but not least are these. Check out the diameter of the microphone
cord and its strain relief to the radio, as well as the size and quality
of any push buttons and control knobs on the front panel. A look at the
external components of the radio will generally reflect the quality of
the internal components that you cannot see. Does the display size allow
you to read it in the roughest conditions as well as direct sunlight?
Does it have enough audio power to be heard when you really need it?
The old adage “you get what you pay for” reigns true when
it comes to marine VHF radios.
Message from Scuba Steve:
Be sure to visit http://www.scubasteve.biz to
make your purchase.