UK radio amateur John Hey G3TDZ (SK) designed the special low frequency radio equipment, the Heyphone, used in the recent cave rescue in Thailand
On Facebook Phil Karn KA9Q posted:
Naturally I got interested in the technical aspects of the cave rescue in Thailand, particularly communications.
They used the “Heyphone”, a voice radio designed by a UK radio ham, John Hey, G3TDZ, as open-source hardware specifically for cave rescues.
It uses upper (single) sideband voice on 87 kilohertz in the VLF (very low frequency) band. (That’s what it says — 87 kHz is actually LF).
The “antenna” consists of two stakes driven into the ground about 20m apart. Enough of the current between them fringes outward to couple to another antenna up to a few hundred meters away (or down).
John Hey passed away in 2016 so he didn’t get to see his work used here. But ham radio should get some of the credit.
John Hey G3TDZ Heyphone Cave Rescue Communication System http://bcra.org.uk/creg/heyphone/
Al Williams WD5GNR has written an article on Hackaday about the cave equipment