VHF Marine Radios
VHF marine radios are essential equipment on a boat.
The usable range of a VHF radio system is dependant on several factors including
the weather, the boat , the antenna and the health of the radio. The most
important part of the system is the antenna. Marine antennas should be mounted
as high as practical. Another important quality of an antenna is it's gain.
Gain is rated in decibels or dB. Most experts recommend
a quality antenna with 6 a gain of dB for powerboats under 50 ft. The antenna
system can be tested by measuring the VSWR of the antenna. The VSWR should
be as low as possible, typically 1.5 to 1 or lower on a healthy antenna.
Other radio problems can stem from the radio or the
vessel electrical system. One of the most frequent radio system failures on a
powerboat is when a poor connection, normally from corrosion, exists between the radio and
battery. The radio will normally come on but may transmit erratically or not at
all. If other accessories like lorans, gps, etc. are on the same circuit, keying
the radio transmitter will likely reset or shut down these units. This is a most
annoying and dangerous problem which is more often than not intermittent. If the
trouble can be duplicated, it can be located easily by checking voltage along
various parts of the radio power circuit while having a helper key the radio.
Battery voltage should be around 12.5 volts and should not drop more than
about .1 volts across any connector, fuse, etc. when the transmitter is keyed.
Some small drop is normal but trouble is likely if the radio is not getting at
least 12 volts all the time.
Receivers, including radios, LORAN units and GPS units
can all suffer from interference on a boat. Much of this can come from other
sources in the boats electrical system. One common example is "clicking" or
"pinging" heard in the radio when a fish finder is on. This and other crazy
symptoms can be minimized by running the proper sized electrical power wiring
for each device all the way to the battery switch. In some cases electrical
filters will need to be installed to combat interference. If you have a problem
like this, call a friend in the electronics business (me) for specifics or see
your local marine electronics shop.
The two new acroynms that boaters may want to learn about
are Digital Selective Calling (DSC) and the Global Maritime Distress and Safety
System (GMDSS). DSC is secure digital format which allows users to communicate
with other DSC equipped radios. In a nutshell GMDSS is a system that allows a
radio to send an automated distress call which can include vessel position
information..... IF....... the radio is connected to a working GPS unit.
If you have a DSC capable radio you will want to obtain an MMSI number. MMSI
numbers are explained and are available from the first link below. The MMSI
number for Daybreak is 338026299.
Several FAQs and webpages explain this in
detail. Here are a few links for more information:
http://www.boatus.com/mmsi/default.htm
http://www.navcen.uscg.gov/marcomms/gmdss/gmdssfaq.htm
http://www.uscg.mil/rescue21/faq/
http://www.ybw.com/ybw/vhf/faq.html
http://www.travelbygps.com/training.php
http://www.bluewatersc.org/radio_procedure.htm
http://portal.etsi.org/erm/kta/maritime/maritime.asp
VHF Marine radio channels
Fittings and Adaptors
There are several types of connectors
found on marine electronics. UHF fittings are the most common, normally on
VHF radios. Another common type is BNC which will often be used on LORAN or GPS
antennas. Other types are mini-UHF, N, SMA and TNC.
The connectors pictured are from left to right:
TNC, BNC, UHF, MINI-UHF, N, SMA
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