ADF or Automatic direction finding is an early term that was distinctive to the DF systems needing manual operations to work. In other words, it is possible to establish a simple and cost-effective RDF system that needs a manual rotation of the antenna and other operator intervention to obtain results. These are categorized in null steering and right left indicator systems. Most of the modern aviation ADFs come equipped with a small array of fixed aerials and make the use of electronic sensors to deduce the direction with the help of strength and phase of the signal emitted from each aerial. The electronic sensors respond to the trough when the antenna is placed at right angles to signal and give the heading to the station with the help of a direction indicator.
- Right left indicator
It is a simple non-automatic DF system that is a biquadrant indicator that needs a frequent physical rotation of the DF antenna. These systems were used mostly on vehicles in mobile RDF applications. When the antenna is mounted accurately on the vehicle, the bearing display indicator informs the operator that only the target transmitter is to the left or right. When the operator applies a certain level of skills, patience, persistence and luck, they can make the most of the transmitter. Albeit the right left indicators were once upon a time used famously in law enforcements application, but now they are replaced by automatic DF systems.
- Non-rotating DF systems
In many older RDF systems, one or more aerials were quickly spun around on a turntable. In the latest non-rotating DF systems, the antenna aerials are stable with any needed rotation achieved by non-mechanical means by electronic switching.
- RMS Bearing accuracy
RMS stands for root mean square. It is a weighted error averaging means which emphasizes mainly on larger bearing errors than the minor ones. RMS averaging has been the averaging technique for quite a while in the DF industry as the standard means for bearing the accuracy.