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The aircraft emergency frequency (also known in the USA as Guard) is a frequency used on the aircraft band reserved for emergency communications for aircraft in distress.The frequencies are 121.5 MHz for civilian, also known as International Air Distress (IAD), International Aeronautical Emergency Frequency, [1] or VHF Guard, [1] and 243.0 MHz—the second harmonic of VHF guard—for military ...
123.1 MHz: Aeronautical Auxiliary Frequency (International voice for coordinated SAR operations). 138.78 MHz— U.S. military voice SAR on-the-scene use. This frequency is also used for direction finding (DF). 155.160 MHz; 172.5 MHz— U.S. Navy emergency sonobuoy communications and homing use.
The civilian aircraft frequency for voice distress alerting is 121.5 MHz. Military aircraft use 243 MHz (which is a harmonic of 121.5 MHz, and therefore civilian beacons transmit on this frequency as well).
All have migrated from using 121.500 MHz as their primary frequency to using 406 MHz, which was designed for satellite detection and location, however most models still broadcast a secondary signal on 121.5 MHz as well, as this helps rescue teams pinpoint the location of survivors once in their vicinity with more accuracy (within 2km) than the ...
Multi-frequency signaling (MF) is a group of signaling methods that use a mixture of two pure tone (pure sine wave) sounds. Various MF signaling protocols were devised by the Bell System and CCITT .
Very high frequency (VHF) is the ITU designation [1] [2] [3] for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high ...
2182 kHz is analogous to channel 16 on the marine VHF band, but unlike VHF which is limited to ranges of about 20 to 50 nautical miles (40 to 90 km) depending on antenna height, [3] communications on 2182 kHz and nearby frequencies have a reliable range of around 50 to 100 nautical miles (90 to 190 km) during the day and 150 to 300 nautical miles (280 to 560 km) or sometimes more at night.
In terms of frequency, this corresponds to a band in the vicinity of 400–790 terahertz. These boundaries are not sharply defined and may vary per individual. [4] Under optimal conditions, these limits of human perception can extend to 310 nm (ultraviolet) and 1100 nm (near infrared). [5] [6] [7]