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Note. – Some ELT’s are equipped with an optional voice capability (A3E) in addition to the A3X emission.
5.2.1.5 The carrier shall be amplitude modulated at a modulation factor of at least 0.85.
5.2.1.6 The modulation applied to the carrier shall have a minimum duty cycle of 33 per cent.
5.2.1.7 The emission shall have a distinctive audio characteristics achieved by amplitude modulating the carrier with an audio frequency sweeping downward over a range of not less than 700 Hz within the range 1 600 Hz to 300 Hz and with a sweep repetition rate of between 2 Hz and 4 Hz.
5.2.1.8 After 1 January 2000, the emission shall include a clearly defined carrier frequency distinct form the modulation sideband components; in particular, at least 30 per cent of the power shall be contained at all times within plus or minus 30 Hz of the carrier frequency on 121.5 MHz.
5.3 SPECIFICATION FOR THE 406 MHZ COMPONENT OF EMERGENCY LOCATOR TRANSMITTER (ELT) FOR SEARCH AND RESCUE
5.3.1 Technical characteristics
Note 1. – Transmission characteristics for emergency locator transmitters operating on 406 MHz are contained in ITU-R Recommendation M.633-1.
Note 2. - Information on technical characteristics and operational performance of 406 MHz ELTs is contained in RTCA Document DO-204 and European Organization for Civil Aviation Equipment (EUROCAE) Document ED.62.
5.3.1.1 Emergency locator transmitters shall operate on a frequency of 406.025 MHz plus or minus 2 kHz. The transmitted frequency shall not vary more than plus or minus 5 kHz in five years including the initial frequency offset. It shall not vary more than 2 parts in 10 to the ninth power in 100 milliseconds.
5.3.1.2 The period between transmissions shall be 50 seconds plus or minus 5 per cent.
5.3.1.3 Over a period of 24 hours of continuous operation at an operating temperature of –20 degrees Celsius, the transmitter power output shall be within the limits of 5 W plus or minus 2 dB.
5.3.1.4 The 406 MHz ELT shall be capable of transmitting a digital message.
[NBAA Note: The above technical specifications can be found in FAA Technical Standard Order (TSO) C-126, available at http://av-info.faa.gov/tso/Tsocur/C126.doc]
5.3.2 Transmitter identification coding
5.3.2.1 Emergency locator transmitters operating on 406 MHz shall be assigned a unique coding for identification of the transmitter of aircraft on which it is carried.
5.3.2.2 The emergency locator transmitter shall be coded in accordance with either the aviation user protocol or one of the serialized user protocols described in Appendix 1 to this chapter, and shall be registered with the appropriate authority.
The above are excerpts from ICAO Annexes. Complete ICAO documents may be ordered from ICAO at http://www.icao.int/cgi/goto.pl?icao/en/sales.htm.
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Emergency Locator Transmitter (ELT) Requirements(6)
