VHF Marine Radios

VHF marine radios are essential equipment for most fishing boats. 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 such as gps units are on the same circuit, keying the radio transmitter will likely reset or shut down these devices. 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.

Marine radios, GPS units, and other devices can suffer from interference on a boat. Electrical interference usually originates 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 odd 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.

Two systems 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.

More Information:

VHF Marine radio channels

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