Radiotriangulation is used for detection of hidden radio transmitters in an important radiosport among radio amateurs, popularly known as "Fox Hunt". Two directional antennas operating from two locations can get the bearings of the signals from the hidden transmitter to get an idea of the location. Same method is used by government officials to locate unauthorized radio transmitters. Similar methods are used by armed forces as well, for obvious reasons. Radio direction finding is useful in ships and aircrafts for radio navigation. It can also be used to track wildlife using radio collars. As is well known for radio amateurs, lower frequency will require antennas of bigger dimension. In case of radio navigation, ships need larger antennas when the radio horizon is nearer so that longer waves which can travel beyond the horizon are needed. Higher frequency and shorter antennas can be used by aircraft when the horizon may extend hundreds of kilometers.
We had a brilliant, but rather obnoxious ham back in the 90's and someone placed an HT that transmitted the dtmf number 9 every few seconds (in a non ham friends home) nearby to said ham on the output of a local machine he frequented. We found it using triangulation and then used the HT's with no antennas to zero in on which apt it was and knocked on the door. The HT was off the air in seconds lol!
