Why do I need a Fixed Mount VHF Radio?

A VHF Marine radio is an important safety device when out on the water, both for use in an emergency and for general communication amongst vessels.

A fixed mount VHF marine radio offers distinct advantages over a handheld device, namely much greater output power (25W vs 5W), the ability to run larger and higher performance antennas, and the benefit of permanent power from the boat’s electronics system rather than relying on a battery pack.

What is DSC?

Digital Selective Calling (DSC) is a means of sending pre-determined digital messages between stations over HF and VHF Marine radio systems.

DSC transceivers are able to send distress alerts which include the vessel’s MMSI number and GPS location along with the time at which that location was determined.

The radio operator can send an alert with a single press of a button and the alert will then repeat automatically.

Marine frequencies – 27 MHz and VHF explained

There are both technical and licensing differences between 27 MHz Marine Radios and VHF Marine Radios.

27 MHz radios are typically utilised on inshore waters, and have a maximum range typically between 8 and 16 km.

VHF radios are both clearer and more powerful and are the radio of choice for offshore use. None the less, they can also be utilised for inshore applications. The maximum range of a VHF radio is typically up to 20 km between vessels or up to 50km from a shore base. (see: range of your signal on the water)

Another big advantage of VHF radios is that VHF communications are monitored by coast stations operated by rescue and other organisations. Vessels can set up logs between themselves and coast stations on coastal voyages, maintaining regular communication, and improving safety.

There are certain usage protocols that must be observed when using a Marine radio. These protocols enable search and rescue authorities to quickly and efficiently assess the situation and act accordingly. Inefficient use of communications equipment can and does, affect the outcome of a problem on the water.

Detailed information about the use of Marine Radios in Australia can be found at the Australian Communications and Media Authority (ACMA) website.

Range of your signal on water

There are two major factors which determine the range you will be able to transmit with your VHF radio. These are the transmission power of the radio itself, and the height of the antenna. VHF transmission is in a straight line. As a result, the curvature of the Earth forms a barrier which limits the distance you can transmit. By increasing the height of your antenna, you can increase the distance before the signal hits the horizon.

You can calculate the transmission distance achievable using the following formula:

Range=1.23√Antenna Height in Feet

So for a mariner using a handheld radio where the antenna is approximately 6 feet above the water, the achievable range is 3.01 nautical miles (5.57km). If the same mariner is talking to another mariner using a handheld radio where the antenna is approximately 6 feet above the water, the two distances are combined, giving a total of 6.02 nautical miles (11.14km).

If the mariner is talking to land base station with an antenna that reaches 400 feet above sea level, and using a fixed mount radio with an antenna that reaches 12 feet above sea level, the distance is far greater at 4.26 nautical miles plus 24.6 nautical miles. This gives a theoretical achievable distance of 28.86 nautical miles.

Other factors which can influence the actual achievable distance include transmission power of the radio, weather as well as obstacles such as islands and waves.

AIS – What Is It?

Automatic Identification System (AIS) is a means of sending and receiving ship information such as identity, position, course, speed, ship particulars and cargo information to and from other ships, suitably equipped aircraft and shore.

AIS is transmitted over the VHF band which ensures functionality even in foggy conditions and near obstacles where the performance of radar systems may be compromised.

Applications for AIS include collision avoidance, traffic monitoring and control, aid to navigation, and search and rescue.

Does the AIST120 send GPS positional information via the NMEA0183 output port?

The AIS cannot provide or output GPS positional information to other equipment via the NMEA 0183 output port.

The NMEA output port only sends received AIS data to a compatible chart plotter using the NMEA protocol.

The AIST120 includes an internal GPS receiver which independently receives GPS Satellite signals to develop the necessary GPS positional fix.

The GPS positional data is attached along with Static-Data (MMSI, Vessel name, Vessel call Sign) when the AIS sends out a vessel Transmission signal.

The AIST120 can only be configured to provide GPS positional output data via the USB port lead. The GPS positional data is available for use with laptop devices using charting software.

Can the AIST120 / AISR120 be wirelessly connected to a laptop or iPad using navigation software?

Not without integrating another device.

The AIST120 and AISR120 are supplied with a USB connection for direct AIS output messaging into PC or MAC applications that operate with Navigation Software. There are products on the market which allow Tablet/ laptop/ iPad users to be able to wirelessly interface with NMEA-type electronic equipment.

A ‘Wireless NMEA Multiplexer’ adaptor is designed to send the NMEA output data from the AIST120 / AISR120 via WiFi to the iPad.

The NMEA output from both AIS products is standardised, thus if the Wireless adaptor allows data transfer without any loss/ or data drop-out, and the user has AIS compatible charting software loaded on the iPad, then it should be possible to wirelessly connect the units.