Heyphone is a communication system for rescue operations in caves. It was used by Thai rescuers come 12 guys from Thai football team and their coach trapped in a flooded cave Tham Luang. All anything, only Heyphone was developed in 2001, and its Creator, an Englishman-radio Amateur John hay, fell asleep in 2016.
The use of this charm for the contemporary realities of the device drew the attention of the Facebook user Phil Karn, who “became interested in the technical aspects of the rescue from the caves of Thailand”, especially communication. Rescuers used radio communication G3TDZ (Heyphone), equipment, open source, specially for this purpose created. It uses upper single sideband modulation at 87 kHz very low frequency range.
The antenna consists of two parts, embedded in the ground at a distance of 20 metres. When a sufficient current is applied, they can “cling” to the other antenna at a distance of 100 meters from them (or even down).
John hay rested in 2016 and have not seen bright enough to use its technology. But the case of Amateur radio lives.
Moreover, Heyphone is no longer recommended for use. He was replaced by Micro Heyphone Ian Cooper, a more modern and updated version of the original device.