EPIRB stands for emergency position-indicating radio beacons. they are self contained radio beacons.
They can be activated either manually (by pressing a button) or automatically (when they float free of a sinking vessel). They should only be set off in a distress situation.
Once set off they transmit a coded message (not voice) to satellites which identify that you are in distress. If you EPIRB includes a built-in GPS it will also transmit your position, if not the satellites can triangulate your position to within a matter of miles within a few hours.
A second radio frequency is also used at close range to pin-point your position.
Note: Some older EPIRBs transmitted on different frequencies and are no longer monitored – check before you buy.
For your EPIRB to be of maximum use you should register it – in the UK that means registering with the coastguard.
See the coastguard website for more details of EPIRP registration.
SARTs or Search and Rescue Transponders are also used in distress situations. When activated they send out a signal when they detect a radar pulse (9GHz), this singal is visible on a radar screen.
It will not identify the vessel but simple display the position of the SART with 12 dots trailing behind it on the screen, as the vessel gets closer the dots turn into dashes and finally as the vessel comes very close to the SART the dashes become concentric circles around its location.
At the sea surface it has a range of 5Nm however an aircraft at 1000m can see it from about 30-50Nm.
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