You'll see "Multi-hop Sky" on page 31 — Page 391, Lesson 398

I want to walk you through the index of this Radio Navigation manual, because the way it's laid out tells you exactly how the subject is structured. We're looking at the entries from the letter M through the start of P, and I'll explain what each of these terms refers to so you have a map of the territory before we dive into any single topic. Let's start with the propagation-related entries. You'll see "Multi-hop Sky" on page 31. That's the propagation path where a sky wave bounces between the ionosphere and the Earth's surface multiple times before reaching the receiver. Each bounce is a "hop," so multi-hop means the signal travels in several arcs rather than one single reflection. Related to that is "MUF," which stands for Maximum Usable Frequency, on page 32. That's the highest frequency that will be refracted back to Earth by the ionosphere for a given path and time — above the MUF, the signal escapes into space instead of coming back down. And "Non-ionospheric Propagation" on page 21 is the catch-all for paths that don't involve the ionosphere at all — like ground waves and direct line-of-sight waves. Now, the modulation and receiver entries. "Narrow Band FM (NBFM)" on page 46 is a frequency modulation scheme with a small deviation, used where spectrum efficiency matters. Then we have a cluster of receiver types. "Multi-channel Receivers" on page 311 and "Multiplex Receivers" on page 311 — these are receivers that can handle multiple channels, with multiplexing meaning several signals are combined onto one transmission path and separated at the receiver. "Multi-mode Receivers" on page 177 can operate in more than one mode, and "Multipath Reception" on page 317 is the phenomenon where a signal arrives at the antenna via two or more paths of different lengths, causing phase interference — that's a real problem in navigation because it distorts the bearing or range reading. Let me pause there — that's the propagation and receiver side. Now I want to cover the navigation aids themselves, because that's the heart of this manual. "Non-directional Beacon (NDB)" on page 85 is a ground transmitter that radiates equally in all directions — it's non-directional — and the aircraft's ADF, the Automatic Direction Finder, measures the bearing to it. "Null Positions" on page 86 refers to the orientations where the received signal strength drops to a minimum, which is how direction-finding equipment determines a bearing. "Omni-directional" on page 112 describes a signal radiated equally in all azimuths, and "Omni-bearing Selector" on page 119 — that's the OBS, the control on a VOR indicator that lets you select a radial. "Operational Range of VOR" on page 116 is the distance within which the VOR signal is usable, and "Outbound Flight" on page 130 is the phase of a VOR procedure where you fly away from the station. Now, the satellite navigation entries. "NAVSTAR" on page 305 is the name of the US Global Positioning System satellite constellation. "Navigation Message" on page 313 is the data broadcast by each satellite containing its ephemeris, clock corrections, and almanac — the information the receiver needs to compute position. "MSAS" on page 320 is the Multi-functional Satellite Augmentation System, a Japanese SBAS that improves GPS accuracy. "NES" on page 321 — that's the Navigation Earth Station, a ground segment component of an augmentation system. And "Multipath Reception" I already mentioned on page 317 applies here too, because multipath is a major error source in satellite navigation. Let me also cover the radar and display entries. "Moving Target Indication" on page 191, abbreviated MTI, is a radar technique that suppresses returns from stationary objects so only moving targets are displayed. "ND" on page 207 is the Navigation Display, the cockpit instrument that shows the aircraft's position and track relative to navigation aids. Now, the signal format entries. "N0NA1A" on pages 49 and 89, and "N0NA2A" on pages 49 and 89 — these are ICAO emission designators. The first character N means unmodulated carrier, the second character 0 means no modulating audio, and the third character A1A or A2A describes the type of modulation — A1A is on-off keying of an unmodulated carrier, which is Morse code telegraphy, and A2A is on-off keying of a tone-modulated carrier. These designators tell you exactly how the signal is modulated, which matters for identifying what kind of transmission you're receiving. Finally, the remaining entries. "Mountain Effect" on page 99 and "Night Effect" on page 98 are propagation anomalies — mountain effect is the distortion of a signal path by terrain, and night effect is the variation in sky-wave propagation at night that causes bearing errors, particularly on NDBs. "Outbound Tracking" on page 93 and "Outbound Track Maintenance" on page 95 relate to flying a track away from a beacon and holding it. "Operational Performance Categories" on page 158 refers to the required navigation performance categories that define accuracy and integrity standards. And "P1" at the very end is just the start of the P entries, which we'll pick up next. So that's the full sweep of this index section. You now have the vocabulary — propagation paths, receiver types, the navigation aids, the satellite systems, the emission designators, and the propagation effects. Each of these will get its full treatment when we reach its page, but you know what every term means at a glance.