During the rescue of the Thai soccer team, Elon Musk’s “kid-sized submarine” dazzled Twitter and the international press. But one of the true technological heroes of the rescue was both less glamourous and more interesting: the HeyPhone, a 17-year-old caving radio, with its entire design available for free online, maintained by a dedicated team of DIY-ers.
On June 26, the British Cave Rescue Council (BCRC) received a call from Thai authorities, asking for its help in trying to locate a lost Thai soccer team. The team of British cave explorers had already aided in similar missions in Europe and North America. The team, which consists of cavers Rick Stanton, John Volanthen and Jason Mallinson, traveled to Thailand with four HeyPhone radios lent by the Derbyshire Cave Rescue Organization. Using the HeyPhones, which are capable of transmitting through hundreds of meters of solid rock, Stanton and Volanthen made first contact with the group, enabling them to transmit messages to the surface.
While the HeyPhones might sound like cutting-edge technology, the devices have a long and fascinating history. The first HeyPhones were designed by John Hey back in 2001 with the support of the BCRC and sister organization the Cave Radio & Electronics Group (CREG).The devices were created to replace the cave-rescue radio Molefone, as that device couldn’t be repaired or replaced once broken. Because of that limitation, the designers of the HeyPhone made all the radio’s documentation widely available, so that cavers could continue repairing their HeyPhones even after there was no official support for them.
The HeyPhone is a standard single-side band radio, which saves power by transmitting on only one of the radio’s “sidebands” of frequency. It has an earth-current system (otherwise known as an end-grounded horizontal electric dipole), where radio frequencies are transmitted through earthed electrodes 25 to 100m (82 to 328ft) apart. While there is still some confusion about how exactly these grounded systems work, the technical manual describes the current "spreading out," taking multiple, curved routes through the ground between the electrodes.
The entire system is made for DIY-ers: the technical manual even recommends earthing the electrodes with metal tent pegs. But it’s precisely that DIY sensibility that has allowed the HeyPhone to stand the test of time, enabling users to modify, fix and improve their radios enough so that they’re still useful in 2018.
For friends and family of the team listening from the surface, the first HeyPhone conversation with the boys provided enormous relief—a comfort that wouldn’t have been possible without the use of a fairly dated piece of equipment designed by and for volunteers. Ultimately, the HeyPhone’s story is a reminder of the power of open-source design—and the fact that newer doesn’t always mean better.
For those interested in learning more about the design of the HeyPhone, or perhaps constructing a HeyPhone of their own, the manual is available here.