chapter  7
Emergency locator transmitters
Pages 1

Several different types of ELT are in current use.

These include the older (and simpler) units that

produce a modulated RF carrier on one or both of

the two spot VHF frequencies used for distress

beacons (121.5 MHz and its second harmonic

243.0 MHz). Note that the former frequency is

specified for civil aviation use whilst the latter is

sometimes referred to as the military aviation

distress frequency. Simultaneous transmission on

the two frequencies (121.5 MHz and 243.0 MHz)

is easily possible and only requires a frequency

doubler and dual-band output stage.