An international distress frequency is a radio frequency that is designated for emergency communication by international agreement.
History
For much of the 20th century, 500 kHz was the primary international distress frequency. Its use has been phased out in favor of the Global Maritime Distress Safety System. Use of some distress frequencies is permitted for calling other stations to establish contact, whereupon the stations move to another frequency. Such channels are known as distress, safety and calling frequencies. Satellite processing from all 121.5 or 243 MHz locators has been discontinued. Since February 1, 2009, the U.S. Coast Guard only monitors distress signals from emergency position indicating radio beacons that broadcast using digital 406 MHz signals. Digital 406 MHz models became the only ones approved for use in both commercial and recreational watercraft worldwide on January 1, 2007.
International distress frequencies, currently in use are:
2182 kHz for medium range maritime voice use. The US Coast Guard has said "beginning August 1st, 2013 the Coast Guard would no longer monitor 2182 kHz". Many other MRCCs, for example most in Northern Europe, now only have MF capabilities and no HF.
Several HF maritime voice frequencies exist for long-distance distress calls:
121.5 MHz is the civilian aircraft emergency frequency or International Air Distress frequency. It is used by some civilian emergency locator beacons; however, the Cospas-Sarsat system no longer monitors the frequency.
406 MHz to 406.1 MHz is used by the Cospas-Sarsat international satellite-based search and rescue distress alert detection and information distribution system
138.78 MHz— U.S. military voice SAR on-the-scene use. This frequency is also used for direction finding.
155.160 MHz
172.5 MHz— U.S. Navy emergency sonobuoy communications and homing use. This frequency is monitored by all U.S. Navy ASW aircraft assigned to a SAR mission.
282.8 MHz— Joint/combined on-the-scene voice and DF frequency used throughout NATO
406 MHz / 406.1 MHz - Cospas-Sarsat international satellite-based search and rescue distress alert detection and information distribution system
GMRS: 462.675 MHz is a UHF mobile distress and road information calling frequency allocated to the General Mobile Radio Service and used throughout Alaska and Canada for emergency communications; sometimes referred to as "Orange Dot" by some transceiver manufacturers who associated a frequency with a color-code for ease of channel coordination, until the creation of the Family Radio Service, in 1996, "GMRS 675" or Channel 6/20 on mobile radios today. Its bandwidth can vary between 12.5, 25 and 50 kHz, and is also allocated to Ch. 20 on 22-channel FRS/GMRS "blister pack" radios. It can have a repeater input frequency of 467.675 MHz, and a tone squelch of 141.3 Hz. After FCC deregulation of simplex FRS/GMRS radios, FRS users may transmit up to 2 watts on the GMRS emergency channel 20 with 141.3 Hz CTCSS, or channel 20-22.
UHF CB : Emergency channels 5/35. Channel 5 is the designated simplex and repeater output emergency channel, while channel 35 is used as the repeater input frequency for duplex operation. UHF CB is only available in Australia and New Zealand.
