Learn/ Extra course/Module 2 of 10
Extra Course, Module 2: Propagation at the Edges
Covers NCVEC 2024-2028 Extra Pool, Subelement E3 (Radio Wave Propagation). Three questions on your exam come from this material.
Ray points the big Yagi at a gray smudge rising over the tree line. "General taught you the ionosphere. Extra teaches you everything the ionosphere is not: the Moon, meteor trails, the paths across the equator, and the solar telemetry behind every forecast. This is the propagation nobody stumbles into. You go looking for it."
2.1The Moon, the Meteors, and the Wave Itself
Begin with the wave, stated with Extra precision. An electromagnetic wave's electric and magnetic fields are oriented at right angles to each other, and the wave travels at a right angle to both fields. Its speed through any medium is set by the medium's index of refraction, which is why "the speed of light" always carries the silent asterisk "in vacuum." And a wave whose electric and magnetic fields rotate as it travels is circularly polarized, a definition that becomes an operating tool two paragraphs from now.
EME, Earth-Moon-Earth, is the longest path in amateur radio: bounce a signal off the Moon and the maximum station separation is about 12,000 miles, any two points that can both see the Moon. The path is brutal, and its physics sets the operating practices:
- Path loss is least when the Moon is at perigee, its closest approach. Serious EME operators schedule by the lunar distance table.
- The returning echo carries libration fading: a fluttery, irregular fading imposed by the Moon's slight rocking, which smears reflections from its rough surface.
- The trip through the ionosphere adds Faraday rotation, twisting polarization unpredictably, and satellites add spin modulation. One antenna choice addresses both: circular polarization, which shrugs at rotation because it is already rotating.
Meteor scatter trades the Moon for ionized debris: a meteor burning up creates a linear ionized region in the E region of the ionosphere, and signals bounce off the trail for the seconds it survives. The frequency sweet spot is 28 to 148 MHz, which is why 6 meters is the meteor band and why the Technician course flagged it years ago.
The rest of the specialized menu:
- Auroral propagation is most likely during severe geomagnetic storms, and the best mode through the shimmer remains CW, the auroral distortion from your Technician course now traced to its solar cause.
- Microwave tropospheric ducts form most often over large bodies of water, with a typical range of 100 to 300 miles, the General course's duct with its geography and mileage attached.
- And the daily ionospheric rhythm, stated as an operating decision: when darkness drops the MUF below your long-distance path, switch to a lower frequency band. Follow the MUF down at sunset, back up at sunrise.
Knowledge Check 2.1
Tap an answer. In your own words first, then check yourself.
1. When is EME path loss lowest?
2. Where does a meteor create its ionized trail?
3. Why does circular polarization help EME and satellite work?
E3A the easy way: all 14 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
E3A01 What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by EME?
Answer 12,000 miles, if the moon is “visible” by both stations
Tip Both stations only need the Moon in view at once, so the surface limit is roughly half the planet, about 12,000 miles.
E3A02 What characterizes libration fading of an EME signal?
Answer A fluttery, irregular fading
Tip The Moon's slight rocking, called libration, keeps shifting the reflection, so echoes come back with a fluttery, irregular fade.
E3A03 When scheduling EME contacts, which of these conditions will generally result in the least path loss?
Answer When the Moon is at perigee
Tip Least loss comes when the Moon is closest at perigee, since a shorter round trip means a stronger echo.
E3A04 In what direction does an electromagnetic wave travel?
Answer It travels at a right angle to the electric and magnetic fields
Tip The wave shoots off perpendicular to both fields, so its direction of travel is at a right angle to E and H.
E3A05 How are the component fields of an electromagnetic wave oriented?
Answer They are at right angles
Tip The electric and magnetic fields always sit 90 degrees apart, at right angles to each other.
E3A06 What should be done to continue a long-distance contact when the MUF for that path decreases due to darkness?
Answer Switch to a lower frequency HF band
Tip As darkness pulls the MUF down, chase it by dropping to a lower HF band.
E3A07 Atmospheric ducts capable of propagating microwave signals often form over what geographic feature?
Answer Large bodies of water
Tip Warm air sitting over cool water builds the inversion, so microwave ducts tend to form over large bodies of water.
E3A08 When a meteor strikes the Earth’s atmosphere, a linear ionized region is formed at what region of the ionosphere?
Answer The E region
Tip Meteors burn up and ionize the air around 60 miles high, which puts that trail in the E region.
E3A09 Which of the following frequency ranges is most suited for meteor-scatter communications?
Answer 28 MHz - 148 MHz
Tip Meteor trails reflect best from 10 meters up through 2 meters, roughly 28 to 148 MHz.
E3A10 What determines the speed of electromagnetic waves through a medium?
Answer The index of refraction
Tip How fast a wave moves through a medium is set by that medium's index of refraction.
E3A11 What is a typical range for tropospheric duct propagation of microwave signals?
Answer 100 miles to 300 miles
Tip Tropospheric ducts usually carry microwaves a few hundred miles, about 100 to 300.
E3A12 What is most likely to result in auroral propagation?
Answer Severe geomagnetic storms
Tip It takes a severe geomagnetic storm to charge the aurora enough to reflect signals.
E3A13 Which of these emission modes is best for auroral propagation?
Answer CW
Tip Aurora smears and distorts a signal, so narrow CW punches through where SSB turns to mush.
E3A14 What are circularly polarized electromagnetic waves?
Answer Waves with rotating electric and magnetic fields
Tip In circular polarization the electric and magnetic fields spin, rotating as the wave moves along.
2.2Paths the Textbook Diagrams Leave Out
The great-circle hop from your General course is the standard model. This section is everything that breaks it, profitably.
Transequatorial propagation (TEP) links stations 2,000 to 3,000 miles apart on a path perpendicular to the geomagnetic equator, with a maximum range around 5,000 miles, and it favors the afternoon and early evening. Ionization bulges straddling the magnetic equator form a double mirror, and stations in the southern US work South America on bands that should be closed. The magnetic equator, note, not the geographic one; propagation follows the field.
Chordal hop is the ionosphere skipping the middleman: successive ionospheric refractions without an intermediate ground reflection, the signal ricocheting along the underside of the ionosphere. Its effect is the payoff: less loss than multi-hop propagation, because every ground reflection the signal skips is loss it never pays. The freakishly loud long-distance signal at sunset is often riding a chord.
The ionosphere also splits every wave it touches into two: the ordinary and extraordinary waves, independently propagating, elliptically polarized waves created in the ionosphere by the interaction with Earth's magnetic field. Two waves, two slightly different paths, and their interference is part of why HF fading is never simple.
The workhorse facts of the group:
- Long-path propagation is most frequent on 40 and 20 meters, the bands with the reach to go the wrong way around profitably.
- 160 meters goes long-distance only on a path entirely in darkness, the D-region absorption story from General taken to its extreme: the top band's DX window is the mutual night.
- Lowering your takeoff angle increases the distance covered by each hop, the single sentence justifying every antenna height decision you will make in Module 7.
- Sporadic E gets its calendar and clock: most likely around the solstices, especially the summer solstice, and most likely between sunrise and sunset. June at midday is the Magic Band's rush hour.
- Ground wave rounds out the map: its range decreases as frequency increases (160 meters crawls a hundred miles; 10 meters barely leaves the yard), and it supports vertical polarization, which is why AM broadcast towers and 160-meter verticals stand up straight.
Knowledge Check 2.2
Tap an answer. In your own words first, then check yourself.
1. What makes chordal-hop signals unusually strong?
2. When does a 160-meter path support long-distance work?
3. When is sporadic E most likely?
E3B the easy way: all 13 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
E3B01 Where is transequatorial propagation (TEP) most likely to occur?
Answer Between points separated by 2,000 miles to 3,000 miles over a path perpendicular to the geomagnetic equator
Tip TEP works best on paths that cross the geomagnetic equator at a right angle, spanning about 2,000 to 3,000 miles.
E3B02 What is the approximate maximum range for signals using transequatorial propagation?
Answer 5,000 miles
Tip Linking the ionized bulge on both sides of the equator stretches TEP out to roughly 5,000 miles.
E3B03 At what time of day is transequatorial propagation most likely to occur?
Answer Afternoon or early evening
Tip The equatorial ionosphere peaks late in the day, so TEP favors afternoon and early evening.
E3B04 What are “extraordinary” and “ordinary” waves?
Answer Independently propagating, elliptically polarized waves created in the ionosphere
Tip The geomagnetic field splits a signal into two independent, elliptically polarized waves inside the ionosphere.
E3B05 Which of the following paths is most likely to support long-distance propagation on 160 meters?
Answer A path entirely in darkness
Tip Topband hates daytime absorption, so 160 meters reaches far only when the entire path is in darkness.
E3B06 On which of the following amateur bands is long-path propagation most frequent?
Answer 40 meters and 20 meters
Tip Long path turns up most often on 40 and 20 meters.
E3B07 What effect does lowering a signal’s transmitted elevation angle have on ionospheric HF skip propagation?
Answer The distance covered by each hop increases
Tip A flatter takeoff angle sends each hop farther, so lowering the elevation angle lengthens the reach per hop.
E3B08 How does the maximum range of ground-wave propagation change when the signal frequency is increased?
Answer It decreases
Tip Higher frequencies are absorbed by the ground faster, so ground wave range shrinks as frequency rises.
E3B09 At what time of year is sporadic-E propagation most likely to occur?
Answer Around the solstices, especially the summer solstice
Tip Sporadic E peaks near the solstices, and the summer one is the strongest.
E3B10 What is the effect of chordal-hop propagation?
Answer The signal experiences less loss compared to multi-hop propagation, which uses Earth as a reflector
Tip Chordal hop skips the lossy ground bounce, so it arrives stronger than ordinary multi-hop.
E3B11 At what time of day is sporadic-E propagation most likely to occur?
Answer Between sunrise and sunset
Tip Sporadic E is a daytime event, happening mostly between sunrise and sunset.
E3B12 What is chordal-hop propagation?
Answer Successive ionospheric refractions without an intermediate reflection from the ground
Tip Chordal hop bends along the ionosphere through several refractions without ever touching the ground.
E3B13 What type of polarization is supported by ground-wave propagation?
Answer Vertical
Tip Ground wave rides on vertical polarization, since the earth would short out a horizontal field.
2.3Reading Space Weather Like an Engineer
The General course gave you the dashboard. The Extra course gives you the telemetry behind it.
The Sun's misbehavior, classified:
- Short-term radio blackouts are caused by solar flares, the 8-minute X-ray strike from your General course, now named as the blackout mechanism.
- Flare intensity runs a letter scale where class X indicates the greatest intensity. An X-flare headline means the low bands are about to go quiet on the daylight side.
- Geomagnetic storms run the G scale, where G5 is the space-weather term for an extreme storm.
- A sudden rise in background noise across a large portion of the HF spectrum signals that a coronal mass ejection impact or solar flare has occurred. The bands tell you before the websites do.
The interplanetary detail that predicts trouble: Bz is the north-south component of the interplanetary magnetic field carried by the solar wind. When Bz points southward, it opposes Earth's field, the two fields connect, and charged particles pour in: southward Bz is the loaded gun of geomagnetic disturbance. Watching Bz turn negative during a CME arrival is watching the storm decide to happen.
The indices, upgraded from General: a rising A-index or K-index indicates increasing disturbance of the geomagnetic field, and the paths that suffer most when they climb are those passing through the auroral oval, the high-latitude ring where the particles rain in. Polar paths die first; TEP, meanwhile, barely notices.
The modern instruments:
- The 304A parameter measures solar UV emissions at 304 angstroms, which correlate with the solar flux index: a direct optical measurement of the ionizing radiation itself.
- VOACAP software models HF propagation, the free planning tool that turns all of this telemetry into a point-to-point reliability forecast.
- And amateur propagation reporting networks (the Reverse Beacon Network and PSK Reporter from your General capstone) report digital-mode and CW signals, real-time confirmation that beats any model.
One last geometry fact files the radio horizon precisely: the VHF/UHF radio horizon is approximately 15 percent farther than the geographic horizon, the Technician course's "slightly past the visible horizon" finally assigned its number.
Knowledge Check 2.3
Tap an answer. In your own words first, then check yourself.
1. Which Bz orientation makes geomagnetic disturbance likely?
2. What does an X in a flare report indicate?
3. What does VOACAP model?
E3C the easy way: all 12 questions, with the right answer
Every pool question in this group. Read the answer, let the tip make it stick.
E3C01 What is the cause of short-term radio blackouts?
Answer Solar flares
Tip A solar flare floods the D region with ionization, causing a sudden short-term HF blackout.
E3C02 What is indicated by a rising A-index or K-index?
Answer Increasing disturbance of the geomagnetic field
Tip A climbing A-index or K-index means the geomagnetic field is getting more disturbed.
E3C03 Which of the following signal paths is most likely to experience high levels of absorption when the A-index or K-index is elevated?
Answer Through the auroral oval
Tip When the A and K indices are high, paths crossing the auroral oval take the heaviest absorption.
E3C04 What does the value of Bz (B sub z) represent?
Answer North-south strength of the interplanetary magnetic field
Tip Bz is the north-south component of the interplanetary magnetic field carried by the solar wind.
E3C05 What orientation of Bz (B sub z) increases the likelihood that charged particles from the Sun will cause disturbed conditions?
Answer Southward
Tip A southward Bz lets solar particles couple in, raising the odds of disturbed conditions.
E3C06 How does the VHF/UHF radio horizon compare to the geographic horizon?
Answer It is approximately 15 percent farther
Tip Atmospheric bending pushes the VHF/UHF radio horizon about 15 percent beyond the visual horizon.
E3C07 Which of the following indicates the greatest solar flare intensity?
Answer Class X
Tip On the flare scale, Class X is the top, the most intense flares.
E3C08 Which of the following is the space-weather term for an extreme geomagnetic storm?
Answer G5
Tip On the G scale for geomagnetic storms, G5 marks the extreme end.
E3C09 What type of data is reported by amateur radio propagation reporting networks?
Answer Digital-mode and CW signals
Tip Reporting networks collect and log the digital-mode and CW signals their stations decode.
E3C10 What does the 304A solar parameter measure?
Answer UV emissions at 304 angstroms, correlated to the solar flux index
Tip The 304A figure measures solar UV emission at 304 angstroms and tracks closely with the solar flux index.
E3C11 What does VOACAP software model?
Answer HF propagation
Tip VOACAP is a predictor for HF propagation.
E3C12 Which of the following is indicated by a sudden rise in radio background noise across a large portion of the HF spectrum?
Answer A coronal mass ejection impact or a solar flare has occurred
Tip A broad jump in background noise across much of the HF spectrum points to a solar flare or a CME impact.
Review: every Exam Anchor from this module
E3A EM wave: fields at right angles to each other, travel at right angles to both; speed set by the index of refraction; circular polarization: rotating fields. EME: about 12,000 miles maximum, both stations seeing the Moon; least loss at perigee; libration fading is fluttery and irregular; circular polarization counters Faraday rotation and spin modulation. Meteor trails: E region ionization; best at 28 to 148 MHz. Aurora: severe geomagnetic storms; CW is the best mode. Microwave ducts: over large bodies of water, 100 to 300 miles. MUF drops with darkness: move to a lower band.
E3B TEP: 2,000 to 3,000 miles perpendicular to the geomagnetic equator, about 5,000 miles maximum, afternoon and early evening. Chordal hop: successive ionospheric refractions with no ground reflection, hence less loss than multi-hop. Ordinary and extraordinary waves: independent, elliptically polarized waves created in the ionosphere. Long path: most frequent on 40 and 20 meters. 160-meter DX: paths entirely in darkness. Lower takeoff angle: longer hops. Sporadic E: solstices (especially summer), sunrise to sunset. Ground wave: range decreases with frequency; vertical polarization.
E3C Radio blackouts: solar flares; class X is the most intense flare; G5 is an extreme geomagnetic storm. Sudden HF-wide noise rise: CME impact or flare. Bz: north-south interplanetary magnetic field component; southward Bz invites disturbance. Rising A or K index: increasing geomagnetic disturbance; auroral-oval paths absorb worst. 304A: solar UV at 304 angstroms, correlated with solar flux. VOACAP: models HF propagation. Amateur propagation networks report digital and CW signals. Radio horizon: about 15 percent beyond the geographic horizon.
Before you move on
The gray smudge over the tree line, for the record, was the Moon, and Ray's point in aiming at it stands for the whole module: Extra-class propagation is deliberate. You now know where the exotic paths live (the Moon at perigee, meteor trails in the E region, the TEP mirrors on the magnetic equator, the chords under the ionosphere) and how to read the solar telemetry that opens and closes them.
Module 3 returns to the bench for the mathematics under everything: resonance with numbers, Q and its bandwidth, phase angles, and the coordinate systems that make complex impedance an ordinary tool.
© 2026 Anthony Pelfanio, K4DIA. All rights reserved.