What is a 406MHz PLB

A 406 MHz PLB (Personal Locator Beacon) is a radio beacon designed to aid in the recovery of people who have, primarily, become separated from their ships at sea or have suffered any form of distress, be it at water or on land.

 A 406 MHz PLB is made up of a small transmitter and a receiver. The transmitter sends out a signal that the receiver picks up. If the person carrying the receiver is close enough to the signal to receive it, they will hear a tone indicating their location

The transmitter emits a continuous frequency-modulated signal at 406 MHz. The receiver detects the signal and converts it back to audio tones. The receiver then displays the user's position on a map.

PLBs were first developed in the 1960s and 1970s, pioneered by David Marshall and in the 1980s, the United States Coast Guard began using them to search for missing boaters. Since then, many countries have adopted the use of PLBs.

In the U.S., the Federal Communications Commission requires all boats over 55 feet in length to carry a PLB. However, the FCC does not require any specific type of PLB. There are several different types of PLBs available. Most PLBs operate on two frequencies: 121.5 kHz and 243 kHz.

  • 121.5 kHz is the international distress channel. It is reserved for use by ships and aircraft operating under International Maritime Organization regulations.
  • 243 kHz is the standard maritime VHF channel. It is primarily used by commercial vessels and fishing boats.​​

406MHz PLBs are typically carried on recreational boats and are reasonably inexpensive, whereas many people who work offshore or on bigger ships will also have PLBs with them, but they are likely to operate on other frequencies such as 121.5MHz. 

Campers and hikers both use 406MHz PLBs. One can activate the PLB if they get lost while hiking or camping. Then, using a handheld receiver, SAR personnel can locate and rescue them. 

406MHz PLBs are also frequently used by inshore fishermen. If a fisherman experiences a Man Overboard incident or drifts away from his boat, he can activate his PLB and send a signal. We would advise anyone who spends time in or around water to carry a personal locator beacon (PLB) in case they become disoriented or distressed.


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