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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 ...
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 (SAR) distress alert detection and information distribution system
121.5 MHz VHF ± 6 kHz (frequency band protected to ±50 kHz) [66] (Satellite detection ceased on 1 February 2009, [67] but this frequency is still used for short-range location during a search and rescue operation) 243.0 MHz UHF ± 12 kHz (frequency band protected to ± 100 kHz) [66] [68] (prior to 1 February 2009 – COSPAS-SARSAT Compatible)
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).
The transmitter component was the BC-778. The frequency was 500 kHz at 4.8 watts, giving it a range of 200 miles (300 km; 200 nmi). Keying could be automatic SOS (including the 4-second long dash for autoalarm), or manual. Crystals for frequency control were a scarce item for the U.S. during the war and the SCR-578 was not crystal-controlled.
For military users, the Emergency has a miniaturized transmitter operating on the 243.0 MHz military aviation emergency frequency. Under normal conditions—flat terrain or calm seas—the signal can be picked up at a range of up to 90 nautical miles (170 km) by search aircraft flying at 20,000 feet (6,100 m). [ 2 ]
2182 kHz is a radio frequency designed exclusively for distress calls and related calling operations [1] in the maritime service. [2] It is equivalent to a wavelength of 137.4 metres. Marine radio transceiver (1.6–26 MHz)
The Royal Navy also deployed direction finding equipment on ships tasked to anti-submarine warfare in order to try to locate German submarines, e.g. Captain class frigates were fitted with a medium frequency direction finding antenna (MF/DF) (the antenna was fitted in front of the bridge) and high frequency direction finding (HF/DF, "Huffduff ...