We're starting a brand-new chapter now: the Automatic Direction Finder, or ADF — Page 80, Lesson 72

We're starting a brand-new chapter now: the Automatic Direction Finder, or ADF. This is one of the classic radio navigation systems, and it's built around a ground station called a Non-directional Beacon, or NDB. Let me give you the lay of the land for this whole chapter, because it's a big one and it all hangs together. We open with an introduction, then we meet the NDB itself — what it is and how it works. From there we go into the principle of operation, which is the heart of the system: how the aircraft actually senses where the beacon is. Then we look at the frequencies and types of NDBs you'll encounter, and the aircraft equipment that receives and displays that information. There's a section on emission characteristics and the Beat Frequency Oscillator, or BFO, which is a piece of audio circuitry you need to understand. Then we cover how the information is presented to you in the cockpit, and the various uses of the NDB. After that, the chapter gets very practical — this is the flying part. We plot ADF bearings on a chart, we maintain a track using the Relative Bearing Indicator, or RBI, and we go through homing, which is just flying straight at the beacon. Then we refine that into proper tracking inbound and tracking outbound, dealing with drift. There's a whole section on drift assessment and how to regain your inbound track, and the same for outbound. We move into holding patterns, then runway instrument approach procedures — the NDB approach, which is a real instrument procedure you'll fly. Finally, we cover the factors that affect ADF accuracy and range, and we close with a summary and the practice questions. So the whole arc is: ground station, aircraft receiver, cockpit display, then all the flying techniques, then the limitations. Let's start at the very beginning with the Non-directional Beacon itself. An NDB is a ground-based radio transmitter. It radiates a signal equally in all directions — that's why it's called non-directional. It doesn't point a beam at you like a VOR radial; it just broadcasts outwards in a circle, and your aircraft's ADF equipment figures out the bearing to it. That's the fundamental idea we build everything else on. Let's move into the principle of operation next.