USASA Direction Finding Operations & Training
Radio Direction finding is concerned with determining the arrival direction of a radio wave. A DF receiver, with associated DF equipment, indicates the approximate direction along an imaginary line on which a transmitter lies. The information obtained by direction finding is seldom accurate enough to direct artillery fire. However, the direction of a distant transmitter can be determined, depending on the DF equipment used, to an accuracy of plus or minus 2 degrees. With the exception of the single station locator, one DF site can only indicate the approximate direction of a transmitter.
Two DF sites, however, can indicate the general location of a transmitter by providing a "cut". Three or more DF sites can provide the fix location of a desired transmitter. The theory of direction finding has remained reasonably static since the early history of the study of electromagnetic wave phenomena. Early radio communications were directional in nature. This was because the radio transmitters were relatively low powered. They were inefficient in their output, and the receivers were relatively insensitive. Efforts were undertaken to "direct" the transmitted wave toward the receiving device to insure communications rather than to determine locations. The useful applications of DF were obtained almost simultaneously with the effort to provide directional transmissions.
There are many uses of direction finding. One example is DF can be used as a navigational aid. ln this capacity, the DF equipment is either used alone or in combination with other DF systems. This depends on the service which is to be provided. Such service includes the positioning, controlling, and homing of ground, sea, and air forces. DF equipment is also used by rescue personnel as an essential part of air-sea rescue. Crash beacons on downed aircraft or disabled ships provide a signal which can be located or "homed-in" on by DF equipment.
The extensive use of military radio communications has increased the value of direction finding in producing signals intelligence. Even if a military force is extremely careful, radio and radar transmissions can be intercepted and the locations of the transmitters determined. Direction finding can provide enemy transmitter locations to intelligence personnel for the construction of enemy order of battle and fusion into other intelligence activities.
Specifically, direction finding can also be used to assist in determining:
- Enemy troops or equipment movements which may in- dicate a possible attack.
- Location of transmitters associated with various weapon systems. (Assists in determining enemy capabilities.)
- New, and confirming known, transmitter locations.
- Possible targets for jamming or intercept.
Above extracted/edited from: DA Field Manual No. FM 34-86 Direction Finding Operations November 1984 version