Let me start with the first entry: TO/FROM appears on pages 118 and 121 — Page 393, Lesson 407

I want to walk you through the index pages of this radio navigation manual. This is the reference map for the entire book, and I want to show you how to read it, because it tells you exactly where every concept lives. Let me start with the first entry: TO/FROM appears on pages 118 and 121. This is the VOR indicator that tells you whether you're flying toward or away from the station. You'll see it again when we study VOR in detail. TONE is on page 89, and TONE/VOICE is also on page 89. These refer to the audio output you select on a VOR receiver — whether you hear the continuous Morse code identifier tone, or the voice transmissions on the same frequency. Tracking Inbound is on page 92, and Track Maintenance is on page 91. These are the two core skills of VOR navigation: maintaining your track, and then tracking inbound to the station. Transmission Power is on page 189. That's about the radiated power of a navigation transmitter. Transponder appears on pages 183, 227, and 247. That's the secondary surveillance radar transponder — the equipment that replies to ground interrogations. Triple IRS is on page 278. That's three Inertial Reference Systems operating together. Tropospheric Propagation Error is on page 317. That's the error caused by the lower atmosphere bending the signal path. TRSB is on page 174. That stands for Time Reference Scanning Beam — the MLS landing system technique. Turbulence is on page 213. TVOR is on page 116. That's a Terminal VOR — a low-power VOR used near airports. Twin FMC is on page 277, and Twin IRS is also on page 277. Those are dual Flight Management Computers and dual Inertial Reference Systems. Twin Pulses is on page 249. That's the paired pulse technique used in DME. Twin Wire Feeder is on page 56. That's the balanced transmission line feeding an antenna. Now moving into the U section. Ultra High Frequency (UHF) is on page 8. That's the band from 300 MHz to 3 GHz. Unique Address is on page 235. That's the individual code assigned to a transponder. Upper Sideband (USB) is on page 44. That's the sideband above the carrier frequency. US DOD is on page 318. That's the United States Department of Defense. User Segment is on pages 307 and 311. That's the GPS receiver portion of the system. UTC is on page 307. That's Coordinated Universal Time — the time standard used in navigation. Now the V section. Variable Phase is on page 112. That's the phase that varies with bearing in a VOR signal. VDF is on page 75, and VDF Summary is on page 79. That's VHF Direction Finder. VDOP is on page 318. That's Vertical Dilution of Precision — the geometric factor affecting vertical position accuracy. Vertical Dilution of Precision is on page 318, the same as VDOP. Very High Frequency (VHF) is on page 8. That's the band from 30 to 300 MHz. And finally, VHF Direction Finder — the entry trails off at the end of the page, but it's the same VDF system we saw earlier. Now, I want you to notice something important about how this index is organized. It's alphabetical, but it's also a map of the whole course. When you see the same topic listed on multiple pages — like Transponder on three pages, or User Segment on two — that tells you the concept is introduced in one place and then applied or expanded in another. When you study, you'll want to read all the listed pages for a topic, not just the first one. Also notice the page numbers themselves. Pages 8, 44, 56 are early — that's the basic radio theory. Pages 89 through 121 are the VOR section. Pages 174, 183, 189 are the DME and transponder sections. Pages 277 and 278 are the FMS and IRS section. And pages 307 through 318 are the GPS and GNSS section. So the index isn't just alphabetical — it's also a chronological outline of how the course builds from basic principles to advanced integrated systems. That's the index. When you're ready, we can move into the actual content — starting with the very first topic, which is the radio frequency spectrum on page 8.