G2 · Published 8 October 2026 · By The Ham Desk

Angles, Paths and the Bands That Behave Differently

This unit takes the same physics further: what the angle of radiation does to where your signal lands, why a path sometimes runs the long way round the world, and why 160 metres and 6 metres are the two bands that ignore most of the rules.

Band 80 m
Study time 18
Level Stretch
questions 10

Waveform and antenna diagram for HF Propagation and Space Weather — HF Propagation and Space Weather — waveform overlay and radiation pattern

Pre-flight briefing

Angle of radiation decides the distance

For a given band and a given layer height, only a limited range of takeoff angles produces a return to earth. The highest angle that still returns a signal is the critical angle: transmit steeper than that and the wave passes straight through the layer into space. Shallow angles give long hops, steep angles give short hops, and the first skywave hop on 40 metres at a low angle may land 400 kilometres away while the same band fired nearly vertically covers 100 to 300 kilometres.

The number of hops determines the total distance. A single F2 hop reaches roughly 4,000 kilometres at a good angle, so a 12,000 kilometre contact is three hops, each with its own loss. That is why multi-hop paths are weaker than single-hop ones even when both ends have the same equipment, and why a path that looks geometrically possible may be unusable in practice.

Short path, long path and the terminator

Every two points on earth are connected by two great-circle routes: the short path, which is the direct way, and the long path, which goes the other way round, 180 degrees different in bearing. Long-path contacts happen when the short path is in daylight or in absorption while the long path is in darkness - typically around sunrise and sunset - and they are recognisable by a signal that arrives from the wrong direction with an echo or a hollow quality.

Two related effects are worth knowing. Signals crossing the geomagnetic equator can be enhanced by transequatorial propagation, a mode that produces surprisingly strong contacts between stations at roughly equal magnetic latitudes. And at the terminator itself, the grey line, absorption along one end of the path is low while the F layer is still illuminated, which is the classic window for 80 metre DX.

The two bands that misbehave

160 metres is difficult for reasons that are mostly not ionospheric. It suffers from high atmospheric and man-made noise because the band is narrow and close to the noise floor, it needs a physically large antenna for efficiency, and in summer the static from distant thunderstorms makes it nearly unusable at any distance. In winter, at night, with a well-designed vertical and a good radial field, it produces intercontinental contacts.

Six metres is the opposite puzzle: it is a VHF band that occasionally behaves like HF. Sporadic E opens it to a thousand kilometres or more with no warning; transequatorial propagation carries it between the Americas and southern Europe or Africa; aurora and meteor scatter support brief contacts at high latitudes. Most of the time it is empty, which is exactly why 6 metre operators spend so long listening.

Terms you must be able to define
Term	What the examiner wants to hear
Critical angle	The steepest takeoff angle at which a signal at a given frequency is still returned by the layer.
Hop	One trip from the antenna up to the ionosphere and back to earth.
Long path	The great-circle route in the opposite direction from the short path, 180 degrees away in bearing.
Transequatorial propagation	Enhanced propagation across the geomagnetic equator between stations at similar magnetic latitudes.
Sporadic E	Unpredictable dense E-region ionisation that opens 6 metres over long distances.

Question deck 10 questions

G3B01 Core

What is the critical angle for an ionospheric layer at a given frequency?

G3B02 Core

Approximately how far can a single F2 layer hop carry a signal?

G3B03 Core

What is meant by a long-path contact?

G3B04 Core

Why is the 160 metre band often unusable in summer?

G3B05 Stretch

What is transequatorial propagation?

G3B06 Core

What does the eleven-year sunspot cycle affect for HF operators?

G3B07 Core

What is a propagation beacon used for?

G3B08 Stretch

Why do contacts on 6 metres often appear with no warning and last only minutes?

G3B09 Stretch

Why is ground-wave propagation significant on the low HF bands but not at VHF?

G3B10 Stretch

A signal arrives from a bearing roughly 180 degrees from the short path with a hollow, echo-like quality. What is happening?

Reference sheet

The explanations for all ten questions sit on this sheet. Pick an answer on the left and the matching card lights up.

G3B01 Explanation 1

Key D — The steepest angle of radiation that is still returned to earth

Steeper than the critical angle and the wave penetrates the layer and is lost to space. This is why NVIS on 40 metres works only up to a point: there is a maximum angle that the F layer can turn back on that frequency.

Rule Fundamentals - critical angle

G3B02 Explanation 2

Key C — About 4,000 kilometres

A good single hop on the F2 layer reaches roughly 4,000 kilometres, so an intercontinental contact of 12,000 kilometres is three hops. Each hop adds loss and each requires the geometry to work out, which is why multi-hop paths are harder than they look.

Rule Fundamentals - hop distance

G3B03 Explanation 3

Key B — The signal travels the great-circle route in the opposite direction from the short path

Two stations are joined by two great-circle routes, and the long path is the one going the other way round the globe. It becomes the better route when the short path is in daylight or in heavy absorption, which is why long-path contacts cluster around sunrise and sunset.

Rule Fundamentals - long path

G3B04 Explanation 4

Key A — Static from distant thunderstorms raises the noise level far above the signals

Atmospheric noise is strongest at the lowest frequencies, and summer thunderstorms across a continent make 160 metres a wall of static. The band improves markedly in winter, when the static quietens and the hours of darkness are long.

Rule Fundamentals - atmospheric noise

G3B05 Explanation 5

Key D — Enhanced propagation across the geomagnetic equator between stations at similar magnetic latitudes

Transequatorial paths cross the magnetic equator and are often stronger than the distance suggests, an effect seen on 6 metres and 10 metres in particular. The geometry requires the two ends to sit at roughly mirror-image magnetic latitudes.

Rule Fundamentals - transequatorial propagation

G3B06 Explanation 6

Key C — The level of ionisation, and therefore how often the higher HF bands are usable

During a solar maximum the F2 layer is dense and the MUF climbs, so 10 and 15 metres open to the world for years at a time. During a minimum those bands may be usable only sporadically, and 20 metres carries most of the long-haul traffic.

Rule Fundamentals - solar cycle

G3B07 Explanation 7

Key B — Transmitting a one-way signal from a known location so operators can tell whether a band is open

Beacons transmit continuously on fixed frequencies, most famously across the 10 metre and 6 metre bands, so hearing one tells you the path from that region is open right now. Software such as WSPR extends the same idea by reporting reception automatically.

Rule 47 CFR §97.203 - beacon stations

G3B08 Explanation 8

Key A — Sporadic E patches are small, drifting and short-lived

The E-region patches that refract 50 MHz are typically tens of kilometres across and drift with the wind, so a path opens and closes as the patch moves. Operators monitor beacons and spotting networks precisely because the window is so short.

Rule Fundamentals - sporadic E

G3B09 Explanation 9

Key D — Ground wave follows the earth's curvature better at lower frequencies and is attenuated rapidly as frequency rises

Ground wave depends on the conductivity of the earth and the frequency: at 1.8 MHz it can cover a hundred kilometres or more over good soil, while at 144 MHz it is limited to little more than line of sight. This is why HF mobile stations keep in touch on 40 or 80 metres over the same distance where 2 metres fails.

Rule Fundamentals - ground wave

G3B10 Explanation 10

Key D — The contact is being made by long path, with the signal travelling the other way around the world

A signal from the reciprocal bearing, deficient in high audio frequencies and often accompanied by an echo, is the signature of long-path propagation. It usually means the short path is in daylight or under absorption while the long path is in darkness.

Rule Fundamentals - long path signatures

How to use this unit

Work the ten questions in one sitting with the reference sheet covered, then uncover it and read every explanation - including the ones you got right. The wording of the real exam is different, so learn the reasoning rather than the answer letters.