Distress Radiobeacon - Traditional ELT, Unregistered

Traditional ELT, Unregistered

The oldest, cheapest (US$ 139) beacons sent an anonymous warble at 121.5 MHz. They are no longer monitored by satellite. They could be detected by satellite over only 60% of the earth, required up to 6 hours for notification, located within 20 km (12 mi) (search area of 1200 km²) and were anonymous. Coverage was partial because the satellite had to be in view of both the beacon and a ground station at the same time—the satellites did not store and forward the beacon's position. Coverage in polar and south-hemisphere areas was poor. The frequency was the standard aviation emergency frequency, and there is interference from other electronic and electrical systems, so false alarms were common. To reduce false alarms, a beacon was confirmed by a second satellite pass, which could easily slow confirmation of a 'case' of distress to up to about 4 hours (although in rare circumstances the satellites could be position such that immediate detection becomes possible.) Also, the beacons couldn't be located as well because their frequency is only accurate to 50 parts per million, and they send only 75-100 milliwatts of power.