The Automatic Direction Finder is an instrument built shortly after the discovery of fire.
It is out of usage now and Non-Directional Beacon (NDB) stations are simply turned off if they break down.
However, despite its slow disappearance, you may very well find one in a plane you fly, and it doesn’t hurt to know how to use it.
The ADF at its core is very simple. It’s just an arrow that points to the NDB station.
Some ADF’s have a moveable compass card in them that can be set when using the ADF. However, many do not contain a gyro and the card will not turn when the plane turns. Rather, you set it while straight and level and use it to navigate. Once you turn you will need to set it again.
There are also ADFs with a slaved compass that rotates to show your current heading. These are more convenient, but either way, it is still a simple instrument.
How to use the ADF
To use it locate an NDB station on your chart with the symbol below.
See the Rainbow NDB station in the center of the image below. The magenta information box to the left contains the name of the station, its frequency (363), its ID (RNB) and the morse code to identify it.
To fly to an NDB station simply tune its frequency and turn so the arrow is pointed up. Don’t forget to listen to the station ID just like you would for a VOR.
It isn’t too much more complicated than that. If you want to approach the station on a specific heading then it helps to visualize your current situation before acting.
For example, say you want to approach Rainbow from directly South of the station. The needle is currently pointing to a heading of 330. This means that you are South East of the station. I like to look at the needle and then point out the window in the direction of the station. It helps me to get more situational awareness and determine which way to go. If you want to approach heading 360 then you will need to go to the left and watch the needle until it is pointing directly North.
Try this out next time you have access to an ADF, because it may be your last chance!
The ADF has one more important but little-known feature. It happens to fall on the same range of frequencies as AM radio so if there are any good stations in your area you can listen to them. Just tune to the station and press the ADF button on your audio panel. Instead of hearing morse code, you will hear AM radio. As you listen, the needle will point to the radio stations antenna as well!