Your Specialists in Radio and Navigation Equipment for use on Land, Sea and Air

MARINE

Q. Are there any special channels I should know about?
A. For 27Mhz marine, the emergency channel is 88. For VHF, the emergency channel is 16.

Q. What is DSC?
A. DSC is known as Digital Selective Calling and is a paging system that uses data signals to automate the transmission and reception of calls on VHF (Very High Frequecy) marine radio channel 70. DSC allows you to call other radios in range to alert of a potential distress. A DSC message automatically indicates the identity of the calling station using a unique MMSI number and the priority / purpose of the distress call.

Q. What is an MMSI number?
A. An MMSI is a 9 digit Maritime Mobile Service Identity number issued by AMSA (Australian Marine Safety Authority) which uniquely identifies your DSC VHF radio once it’s registered at www.amsa.gov.au.

Q. What other features can DSC offer?
A. If your DSC radio is interfaced with a GPS receiver, it will be be able to transmit crucial vessel information as well as you position in longitutude and latitude. Some of the top-end DSC VHF radios such as GME’s GX600D, also send out the nature of the distress call such as: undesignated, fire, flooding, collision, grounding, capsize, sinking, adrift, abandoning, piracy and MOB (Man OverBoard). With a Garmin GPS chartplotter interfaced, the GX600D allows communication with another boat or group of boats using MMSI numbers to send, receive and display each others positions. The GX600D also boasts a feature known as position polling which allows another station (ship or shore) to automatically request your DSC radio to send it GPS position which is ideal for fleet or regatta management.

Q. Do I need a license to operate on VHF or 27Mhz?
A. 27Mhz is known as the citizen band. No license is required to operate a 27Mhz marine transceiver. VHF marine transceivers however, require a minimum qualification of an MROVCP (Marine Radio Operators VHF Certificate of Proficiency) to legally operate on this frequency band (with or without DSC). More information relating to qualifications, licensing and DSC operations can be found in The Marine Radio Operators Handbook produced by the Australian Maritime College at www.amcom.amc.edu.au.

Q. How does a fishfinder work?
A. Fishfinders (depth sounders) use sonar (SOund NAvigation and Ranging) sound waves to transmit a sound pulse by sending short bursts of electrical energy into a transducer. The transducer then converts the electrical energy into a cone of sound wave energy which travels through the water and reflects off objects such as sand, mud, rocks, seaweed and fish. The transducer then receives the sounds of any returning echos which are amplified and processed by the fishfinder to be displayed as a graphical image on the screen.

Q. What are thermoclines?
A. Within large bodies of water, the temperature differs from the surface to the bottom and are made up of warmer and cooler layers. Where these layers meet is called a thermocline. This layer of different temperature causes a change in the speed of the sound wave which makes the layer visible on fishfinders.

Q. What is whiteline on a fishfinder?
A. A whiteline helps determine whether the sea bottom is hard or soft. Generally, a stronger echo received by the fishfinder, the thicker the whiteline is displayed and harder the sea bed will be. This feature helps with identifying areas particular schools of fish frequent.