Side Band Transceivers - updated September 2009
by Chuck Husick
Boats that venture
off-shore will quickly move beyond the normal communication range of VHF
radio. Although the 406 MHz EPIRB system provides remarkable emergency
signaling capability, it is an emergency one-way system. Maintaining communication,
for both routine and emergency purposes requires the use of either satellite
or high frequency (HF) radio.
The same electronic
developments that have so remarkably influenced VHF radio transceivers
have made HF radios capable of world-wide communication practical for
even small boats.
This method of radio communication differs from both the narrow-band FM
system used for marine VHF radio and from the double sideband amplitude
modulation system employed for conventional AM broadcast radios. Single
sideband (SSB) modulation provides the advantage of using all of the available
transmitter power to convey information using voice or digital means.
Typical uses include communication with commercial high frequency shore
stations that can connect to the world's telephone system, communication
with other vessels and amateur (ham) radio.
cruising sailors find that the SSB "Nets", informal groups
of ham operators who communicate on specific frequencies at preset
times are an invaluable resource. The use of SSB frequencies allows
much wider area coverage than is possible on VHF. The exchange of
information includes weather, notice to mariner information of possible
value to those transiting the area, arrangements for meetings of
friends and so long as no commercial value is involved, arrangements
for obtaining repair parts when sailing in out of the way places.
Obtaining a ham license is now much easier than ever before. The
FCC deleted the Morse Code requirement from the Amateur Radio Service
Part 97 rules on 23 February, 2007. Unlike other radio station licenses,
there is no charge for a ham license
While marine VHF radio
transmitter power is generally limited by law to 25 watts, HF-SSB sets
are generally capable of emitting between 100 and 150 watts of peak envelope
power (PEP). These power levels, when delivered to a properly designed
antenna system and using the appropriate frequencies, can provide communication
over distances of hundreds to tens of thousands of miles. The wiring that
supplies DC power for the SSB set must be properly sized for the radio's
peak current drain and the distance from the boat's battery. Although
the average transmitting power drain of a 150 watt PEP radio won't exceed
5 amperes at 12 volts, the momentary peak drain can reach 25-30 amperes.
Short wave signals
do not travel far along the earth's surface. Communication over very long
distances transmitted signals proceeding upward in the
atmosphere encounter a layer of air molecules that have been electrically
modified by energy from the sun. These layers can act as mirrors, reflecting
the radio energy downward toward the surface of the earth. In effect,
the transmitted energy bounces off the high altitude layer and can then
be received at a point far distant from its origin. The altitude and the
reflecting quality of the ionized reflecting layers in the atmosphere
is influenced by the season of the year and the time of day at both the
transmitting and receiving stations. Establishing communication over long
distances therefore requires choosing frequencies that will return to
the earth's surface at the location of the listener. Numerous aids are
available to guide the choice of appropriate frequency.
The microphone used
with the HF set and the way it is used can determine the ability of the
remote listener to understand your message. As with VHF sets, the microphone
is designed to be held close to the user's mouth, no more than an inch
or two away. It is best to use the mic in as quiet an environment as possible.
Since most HF communications can occur from a below deck position wind
noise won't normally pose much of a problem.
HF-SSB sets can be
used with various types of modems (modulator-demodulator) to provide digital
communication capability. Some modems allow a computer to be used as a
form of teletype, others allow the computer to send and receive e mail
via the radio. The e mail services available include commercial providers
such as WLO, Mobile, Alabama and PinOak, in New Jersey. Licensed amateur
radio operators can use e mail services provided on a voluntary basis
by some ham organizations such as Sail Mail andWinLink. HF-SSB radios
also have great value in receiving weather reports and notices to mariners
and can be connected to computers to decode weatherfax transmissions.