The website Inverse has an interesting article on Amateur Radio direction finding:

Radio direction finding has existed for nearly as long as radio itself (the late 19th century). The military uses it for practical reasons, utilizing it to 'triangulate,' or locate, hidden military bases, transmitters, and submarines that would otherwise be a secret. (The basic technique, with different technological adaptations, was used in both World War I and World War II.) Now, radio direction finding has become a sport that combines the geeky charm of ham radio, the outdoor skills of orienteering, and the endurance of cross country.

Bob Frey is an ARDF athlete who has competed since 1999 and has attended four World Championships. "It’s a mental game of hide and seek,” Frey tells Inverse. "There’s so many parts to it. [You’re thinking], Where am I? Which direction is the transmitter? Hopefully I don’t get lost.”

Even the best competitors will admit they do get lost on occasion. But there’s something about the sport that keeps competitors coming back year after year. It’s the rush of racing mixed with the pride that comes from knowing you can trust your brain under pressure.

Jerry Boyd has been an ARDF competitor since 1999 and has attended three World Championships. "If you want to compete, you have to move fast,” Boyd tells Inverse. "It’s thinking on the fly.”

WHAT MAKES AMATEUR RADIO DIRECTION FINDING A SPORT?
To really understand ARDF, you need to know the basics of how radios work.

Radio transmitters release radio waves that are then picked up by radio receivers (the antenna used by ARDF athletes). These transmitters and receivers are usually designed to work within a pre-specified set of frequencies, measured in hertz. Two of the major ARDF competitions require tracking down transmitters attuned to one of two frequencies: 3.5 megahertz (also called an 80-meter competition) or 144 megahertz (also called a 2-meter competition).

Each frequency creates a different flavor of competition, explains Ole Garpestad. He is the vice president of the International Amateur Radio Union (IARU), an international governing body for ham radio operators. Garpestad has been presiding over the Amateur Radio Direction Finding World Championships since the first one was organized in the 1980s.

The 3.5 megahertz competitions require receivers with large antennas. Those are cumbersome to run with (people get around this by building them out of flexible materials that can move through brush, like tape measures), but they provide steady and accurate signals that make navigating easier.

"It’s good for a starter,” Garpestad tells Inverse. "It’s even better for a fast runner.”

The 144 megahertz waves don’t pass through large objects and instead might be reflected around the forest. Each one of those reflections is about 60 to 70 percent accurate, but following any one signal with too much confidence can lead a competitor down a false trail. This can even happen to seasoned competitors, like Joseph Huberman, an ARDF athlete from Raleigh, North Carolina, who has competed in five World Championships.

Read more at
https://www.inverse.com/mind-body/not-sports-amateur-radio-direction-finding