Pulse Recurrence Frequency, or PRF, is how many pulses are transmitted per… — Page 393, Lesson 402

This is the index of the book, so I want to walk you through what these entries actually mean as a map of the ground we're about to cover. Think of this as your first look at the territory — every one of these terms is a technical concept we'll build on, and I want to give you the professional definition now so the names aren't strangers when we meet them in the chapters. Let's start with the pulse family, because that's the heart of radar and DME. Pulse Length is the duration of a single transmitted pulse, measured in time — typically microseconds. Pulse Recurrence Frequency, or PRF, is how many pulses are transmitted per second. And Pulse Recurrence Interval, or PRI, is the time between the start of successive pulses — it's the reciprocal of PRF. So if PRF is pulses per second, PRI is seconds per pulse. Pulse Modulation is the technique of encoding information onto a carrier by varying the pulse characteristics. And Pulse Technique refers to the method of using pulses for ranging or interrogation — you'll see it at pages 185 and 247, which is DME and SSR territory. Now the navigation geometry. Pseudo-range is the measured distance from a satellite to a receiver, but it's called "pseudo" because it includes clock errors — it's not the true range until you correct for those errors. That's pages 314 and 315, in the GNSS chapter. Pseudo-random Noise, or PRN, is the code sequence a satellite transmits — it looks like noise but it's actually a carefully generated, repeating pattern that lets the receiver identify which satellite is which and measure the pseudo-range. PZ90 is the name of the Russian geodetic reference frame used by GLONASS — it's the coordinate system that defines where the satellites are. Pythagoras at page 211 — that's the geometry behind radar ranging and some navigation solutions. Right-angle triangles, the square of the hypotenuse equals the sum of the squares of the other two sides. It shows up in radar beam geometry. Now the Q-codes — these are the standard aviation shorthand for bearings. QDM is the magnetic bearing to the station — the heading you'd steer to fly directly to the beacon. QDR is the magnetic bearing from the station — the radial you're on. QTE is the true bearing from the station, measured from true north instead of magnetic. And QUJ is the true bearing to the station. So QDM and QDR are magnetic, QTE and QUJ are true, and the "M" and "R" tell you whether it's to or from. These are fundamental to VOR and NDB navigation. Quadrantal Error at page 100 — that's an error in an ADF or radio compass caused by the aircraft's metal structure distorting the received signal. It's maximum at 45, 135, 225, and 315 degrees relative to the aircraft — the quadrants between the cardinal headings. Now radar. Radar itself is Radio Detection And Ranging — you transmit a pulse, listen for the echo, and measure the time to get range. Radar Aerials are the antennas — at page 60, that's the physical structures that focus and steer the beam. Radar Beam is the concentrated cone of energy the aerial radiates. Radar Frequencies — the specific bands radar operates in, page 185. Radar Resolution is the ability to distinguish two separate targets as two distinct echoes — both in range and in bearing. Radar Shadow is the area behind a target where the beam can't reach, so targets in that shadow aren't detected — page 218. Radial — that's a line of constant bearing from a VOR station, measured from magnetic north. Radial Interceptions — the technique of flying a heading to intercept a specific radial at a desired angle. Range Search — that's a radar or DME technique for scanning through range values to find and lock onto a target, pages 247 and 249. Radio Magnetic Indicator, or RMI — that's an instrument that combines a compass card with a bearing pointer, showing you both your heading and the bearing to or from a station. Pages 90 and 122. Range Error at page 321 — that's the error in a satellite pseudo-range measurement caused by things like atmospheric delay or clock inaccuracies. Rate of Descent at page 162 — that's the vertical speed, in feet per minute, at which the aircraft descends — relevant to approach procedures. And RBI — that's the Relative Bearing Indicator, the older instrument that shows the bearing of a station relative to the aircraft's nose, not referenced to a compass card like the RMI. So this index is your table of contents for the whole radio navigation syllabus — pulse techniques, Q-codes, radar, VOR radials, and satellite ranging. Each of these names is a concept we'll unpack properly as we go through the chapters.