Still, in some cases that’s enough information. So if the antenna is pointing north, the signal might be to the north but it could also be to the south. You can’t actually tell which side of the antenna is pointing to the signal with a loop or a dipole.
British radio direction finding truck from 1927 public domain
By 1900, experimenters noted dipoles exhibit similar behavior and it wasn’t long before antennas were made to rotate to either maximize signal or locate the transmitter. In 1888, Heinrich Hertz noted that signals were strongest when in one orientation of a loop antenna and weakest 90 degrees rotated. However, it might surprise you that direction finding is nearly as old as radio itself.
We think of radio navigation and direction finding as something fairly modern.
