What Types of PLB Are There?

What is the Difference Between an EPIRB, ELT and PLB?

EPIRB - Emergency Position-Indicating Radiobeacons

EPIRBs are used in ships and boats and are designed to float upright using the water plane as a reflector to more efficiently get the signal to the satellite. For this reason they have ballast built in and need to be a certain minimum size to ensure they float correctly and their size and weight make them impractical for use by bushwalkers.

EPIRBs are commonly confused with PLBs. Whilst they are both distress beacons they are intended for different purposes and EPIRBs are not suitable for bushwalking. AMSA has discussed with BWRS its wish for the correct terminology to be used for beacons, so please try to refer to the units suitable for bushwalking as "PLB".

ELT - Emergency Locator Transmitters

ELTs are designed for aviation and are larger, generally fixed units in aircraft that are automatically activated when an aircraft crashes. Again they are not suitable for bushwalkers as they are too large and heavy.

PLB - Personal Locator Beacon

PLBs for bushwalking use are called Personal Locator Beacons or PLB. These are small, lightweight units suitable for bushwalking use. The remainder of this page will discuss PLBs.

 

 

What is the New and Old Distress Beacon Systems?

Decommissioned 121.5MHz/243MHz Analog Distress Beacon System

The satellite monitoring of these frequencies ceased in 2009, but land based receivers, shipping and aviation still monitor it. This means a beacon activated on this system requires a land receiver, aircraft or ship to be close enough to receive the signal; then the pilot/captain needs to be monitoring the channel, detect the signal, perform direction finding procedures and report it to authorities. This is patchy and random at best so is therefore totally unsuitable for an emergency system. No reputable retailer will sell you a PLB on this system as it will no longer function reliably.

There has been comments that it is illegal to activate a beacon on this frequency. This is not true, it remains legal to activate a beacon on this frequency as the Radio Communications Act allows anybody to use any frequency in an emergency. Additionally, the new digital beacons also transmit on 121.5MHz so it clearly is legal to activate a beacon on 121.5MHz in an emergency.

As mentioned above, all beacons on this system should be disposed of through your nearest Battery World shop.

However, it is instructive to have a look at how the old system worked.

The old 121.5MHz/243Mhz system works by transmitting a simple pulsed tone on one or both of 121.5MHz and 243MHz. The signal then relies on direction finding by the satellites, aircraft and ground stations receiving the signal to determine the position of the beacon. This often requires several satellite passes before a location of useable accuracy is determined - AMSA indicates the average time for an initial alert from a satellite is 90 minutes but could be anywhere from minutes to 5 hours depending on the satellite passes over Australia at the time of activation. This means you may have to wait some time even before the alert is raised in the RCC. Even after the satellite fix is determined it is only accurate to within 20 km. For PLBs activated in remote areas the usual procedure is to send a rescue helicopter with radio direction finding equipment to home into your exact location. It is common for the helicopter to take some time with direction finding, especially if the beacon is in an area such as a canyon or gorge as the signal may be masked by the high walls and not picked up until the aircraft is almost overhead or the signal could bend and reflect around the local landforms.

The major problem with this system was that it had an overwhelming number of PLB activations were false alarms - AMSA indicates about 97% of activations were false alarms. However, when an PLB is detected there is no way of knowing whether it is a genuine emergency or not so they must assume it is genuine and send in resources to track it down. This makes it a very inefficient and expensive system. This problem is one of the major reasons the satellite tracking of 121.5MHz was ceased in February 2009.

406MHz Digital Distress Beacon System

This is the newer system which has a number of upgrades over the older system. The 121.5/243MHz system was a simple analog system, but the 406MHz system is digital and therefore allows more information to be sent when a beacon is activated. All digital PLBs on 406MHz transmit a unique identifying number and can be correlated to a database of registered owners of beacons. This means if you get a 406MHz PLB you should register it with AMSA straight away! The advantages of this identifying signal are:

  • Authorities know straight away whether the signal is received from a boat, aircraft or a bushwalker and can deploy resources appropriate to the incident more quickly.
  • Many false alarms can be eliminated easily as the received signal's identification can be referenced to the registered owner of the beacon. The owner can then be contacted and the details of the incident established quickly;
  • It has a stronger signal strength so is more likely to be received from marginal areas such as gorges and under a tree canopy.

Although the 406MHz system relies on the same polar orbiting satellites used by the 121.5MHz beacons, there are also satellites in geo-stationary orbit over the Equator that can receive signals from 406MHz beacons. This is one of the major differences that make the 406MHz system far superior to the analogue 121.5MHz system as the geo-stationary satellite detections are displayed in the RCC within minutes of activating a beacon. Users must be aware that that a beacon must have line of sight to the geo-stationary satellite - that will be low on the northern horizon for users in the southern states of Australia. Signals will be blocked by rock outcrops and heavy foliaged canopies. Beacon users should also be aware that the basic 406MHz beacon will not generate a position when its signal is received over a geo-stationary satellite but an alert will nonetheless be received at the RCC and the search and rescue (SAR) officers will have important contact details from the registration database allowing search activity to begin even without a position. Obviously a lot less can be done with this initial alert if the beacon is not registered. That is why registering your beacon is very important.

Other advantages of the new 406MHz system include:

  • The 406MHz system provides alerts far more quickly with alerts being received within minutes from the satellites in geo-stationary orbit over the Equator.
  • The 406MHz beacons are fixed by the polar orbiting satellites to within 5km, so the rescuers are closer to you before they need to start direction finding.

The digital beacons also transmit on 121.5MHz to ensure that aircraft can continue to easily locate the beacon by using radio direction finding techniques.

Because 406MHz beacons are digital there is the capability to transmit additional information in the alert. Some beacons have a GPS capability which activates a GPS engine onboard when the beacon is switched on. The position from the GPS is transmitted to the satellites and relayed to the RCC and locates the beacon far more accurately (<120 metres) than is possible with the Cospas-Sarsat system alone. The use of a GPS capable 406MHz PLB results in a very accurate position being received via the geo-satellite within minutes of the beacon being activated. Not only is the alert received quickly but for bushwalkers in remote and rugged country, the accurate position means that searchers will locate them far more quickly.

BWRS recommends only using 406MHz PLBs with a GPS function.

Up until recently 406MHz beacons were heavy and bulky but this has improved dramatically with new PLB models released by several manufacturers. Good examples are the GME MT410G, or the McMurdo FastFind ranges. Each of these units weighs under 250g and can fit in your pocket and are therefore ideal for bushwalking. They all have the GPS beacon as an option.

Some prices are for the new digital units from a quick look on the web include (these prices are as of September 2012):

 

GME MT410G
McMurdo Fastfind 211 PLB (with GPS)
ACR Cobham ResQLink 406 MHz GPS

 

All 406MHz beacons should be registered. Registration is free and can be done here.

Be aware that some overseas beacons are not compatible with the Australian system. The safest way to avoid this problem is to purchase your PLB from a reputable Australian retailer, but if you wish to purchase internationally you must ensure the unit you are purchasing is compatible with the Australian system. Further information on this issue can be found here.

See the Australian Maritime Services Authority website for a more detailed information about the system and how to use it.