EPIRB Frequency Guide for Sailors

An EPIRB operates primarily at the 406 MHz frequency band, which is monitored by the COSPAS-SARSAT satellite system and is detectable by satellites globally.

The comprehensive coverage and range of this technology ensures that distress signals can be transmitted from anywhere in the world.

A secondary frequency, 121.5/243 MHz, acts as a homing signal for local search and rescue operations, although it’s less common since it is not satellite-monitored.

  • Primary frequency: 406 MHz
  • Secondary frequencies: 121.5/243 MHz

Signal Structure

The signal sent from an EPIRB includes a unique identifier and a data burst containing crucial information.

This structure is capable of being detected by both COSPAS-SARSAT satellites and in some cases by GOES weather satellites.

The standard alarm signal is an AM signal, with characteristics designed specifically for satellite detection and interference avoidance:

ModulationTone sweep
Amplitude modulated (AM) signal1600 Hz to 300 Hz, 2-4 sweeps

GPS Integration

Modern EPIRBs are often equipped with GPS, enhancing the accuracy of the distress signal’s location data.

Once an EPIRB is activated, it transmits GPS coordinates along with the distress signal to the 406 MHz satellite network, greatly improving response times.

The result is faster pinpointing of your location for the search and rescue team from the transmitted GPS coordinates.

Types of EPIRBs

As you know by now EPIRBs use a frequency signal of 406 MHz. A Personal Locator Beacon (PLB) can be thought of as a type of EPIRB and also operates on the same frequency.

I’ve detailed the difference between EPIRBs and PLBs to teach you the ins and outs of both. But here’s a quick recap.

Category I EPIRBs are designed to automatically deploy. In an emergency situation, these beacons float free from their brackets and activate themselves upon contact with water.

As a result, they are detectable by satellites anywhere in the world, significantly increasing the chances of a timely rescue.

In contrast, Category II EPIRBs require manual activation by you or someone else on your vessel.

These are typically mounted or stored in an accessible location so they can be quickly activated in an emergency.

While some models may also activate upon submersion, their need for manual activation is what distinguishes them from Category I EPIRBs.

Personal Locator Beacons (PLBs) are smaller, personal devices and can be carried by individual people rather than being mounted on a vessel.

They serve a similar function to EPIRBs but are designed for personal use in remote locations to ensure individual safety.

Although they require manual activation, PLBs are compact and can be attached to life jackets or personal gear for easy access.

Registering your EPIRB is paramount and links your device to crucial contact information, which is vital in emergencies. You should register your EPIRB with your national authority, ensuring that all details are up-to-date.

If you own a private boat, you’re not exempt from compliance. Although not always mandatory, equipping your vessel with an EPIRB that meets performance standards and ensuring its registration enhances your safety at sea.

Alert and Distress Signal Processing

Once activated, your distress signal is captured by satellite systems, decoded, and relayed to search and rescue authorities who initiate the proper response to locate and assist you.

Reception by Satellites and Ground Stations

The distress signal transmitted by your EPIRB is received by two principal satellite systems: GEOSAR (Geostationary Search and Rescue) and LEOSAR (Low-Earth Orbit Search and Rescue).

The powerful LEOSAR satellites utilize the Doppler shift in signals to determine your beacon’s position with increased accuracy.

For immediate and continuous coverage, the GEOSAR satellites provide a persistent watch but without the Doppler positioning advantage.

After satellite reception, signals are directed to Local User Terminals (LUTs), which process the information and forward it to the appropriate Rescue Coordination Centre (RCC).

GEOSARProvides continuous coverage; no Doppler information
LEOSARCalculates position using Doppler shift; intermittent coverage
Doppler ShiftThis effect is used by LEOSAR to improve location accuracy
LUTsGround stations that receive your distress signal from satellites

Relay to Search and Rescue Authorities

On receiving your distress signal, the rescue co-ordination center (RCC) initiates the deployment of search and rescue resources.

They utilize tracking equipment and, if your EPIRB is equipped with AIS (Automatic Identification System) signals to pinpoint your location.

The 406 MHz frequency is key for enabling effective global coverage and swift response times.

The National Oceanic and Atmospheric Administration (NOAA) in collaboration with INMARSAT E enhances the overall efficiency of distress alerting.

Your EPIRB’s signal integrity and quick processing are essential in effectively conveying your emergency.

RCCA hub that coordinates search and rescue efforts upon receiving the signal
AISAn additional communication layer that can improve localization
NOAA & INMARSAT EAgencies and systems that work to ensure fast and accurate signal relay to rescuers
Distress AlertingThe process whereby your emergency signal is identified and acted upon

Frequently Asked

EPIRBs are designed to signal distress to search and rescue satellites, providing location data for maritime emergencies. Conversely, SARTs (Search and Rescue Transponders) are radar-based, responding to nearby ships’ radar signals to indicate position during search and rescue operations.

A 406 MHz EPIRB has several advantages, including global satellite reception, enhanced location accuracy, and the ability to encode identifying information into the distress signal. In contrast, the 121.5 MHz and 243 MHz models have more localized coverage and lack the digital capabilities of their 406 MHz counterparts.

The Cospas-Sarsat system employs the 406 MHz frequency band to detect and locate EPIRBs.

Once activated, the EPIRB’s signal is picked up by the system’s satellites. The ground stations then process the signal and relay it to the nearest search and rescue authorities, significantly expediting the rescue process.

I’m the founder and chief editor here at Sailing Savvy. I spent a decade working as a professional mariner and currently, I mix those experiences with digital publishing. Welcome, and I hope that we can be the hub you need for safe passage.