Last Updated on May 13, 2026 by John Berry
This page attempts to give a background to understanding how far signals can go for a given frequency, time of day and atmospheric characteristics. It aims to describe propagation modes, and in so doing, give understanding of broad propagation range limits.
It should be read along with the other page here on ground wave, space wave and sky-wave. In essence those are the three high level modes. This page drills down a little to the descriptive level below. Further layers of description about each propagation mode are given throughout this site.
Propagation modes
A propagation mode describes the mechanisms by which a signal gets from one station to another. It’s not to be confused by modulation mode which describes how information is impressed on the signal.
Propagation is all-at-once. The wave is launched. One propagation mode proves better than another and the communication works over that path for that system value. Radio amateurs can bias their antennas to more likely exploit one propagation mode or another, but it’s a bias, not a switch. Signals still simultaneously propagate by favourable and less favourable modes. And signals still arrive at the distant station by several modes, sometimes causing multi-path interference that manifests as fading.
As I note on another page, signals can propagate in the troposphere, or they can go up to the ionosphere and be refracted and reflected back to Earth.
Ground, space and sky all at once
On any day when working stations on 50MHz during a Sporadic E opening, the PSK Reporter site (https://pskreporter.info/) will show reception of your data signals worldwide. On a good day, there will be three (and maybe even five) groupings and these are shown bulleted below. This example is for 50MHz. A similar but unique description can be made for every band on which radio amateurs operate.
- Those from your station out to about 500km where propagation is in the troposphere;
- Those in a band at 1,000km distance, plus or minus about 250km where propagation is via the E Region. This is given the mode designation 1E – one hop via the E Region (around 100km up).
- Those out to about 2,400km distance, plus or minus about 500km. This propagation mode is via 2E. The general designation Es tends to be used when it is believed that propagation is via sporadic excitation of the E Region.
- Those at greater distance from about 3,000 to about 5,000km or more might be via the F Region. If the mode is believed to be via the F1 region, this carries the designation F1. Likewise for F2. That DX would include west coast USA and the Caribbean
- DX is available for very small percentages of time to South America and Japan. In these cases propagation is complex. In this case the mode might be 1F1Es1F1 comprising one hop of F1, chordal hope propagation within E, then 1F1 again. Many other options are possible.
System values for many modulation modes and equipments allow many thousands of kilometres to be covered. Whether communication results depends on the propagation mode.
Describing the modes
The diagram below illustrates graphically five propagation examples. The table below sums up the diagram with associated propagation mechanisms to give a general model. The model covers tropospheric and ionospheric propagation (via both E and F regions).
| No. | Path | Propagation mode | Losses include | Propagation range limit |
|---|---|---|---|---|
| 1 | Within the horizon. | Tropospheric line of sight and near line-of-sight space wave. Ground wave at LF and lower HF. | Free Space Loss, multiple knife edges, diffracted sub-path and clutter losses. Ground losses. | 5-50km |
| 2 | Beyond the horizon. | Tropospheric by diffraction. | Propagation by diffraction over rounded (often Earth bulge) obstruction. | 50-700km |
| 3 | Skywave | Ionospheric, reflected & refracted in E Region during aurora, sporadic E, meteor scatter and other E Region events. | Free Space Loss. | 1E, nominally 1,200km. (1,000-1,500)km |
| 4 | Skywave | Ionospheric reflected & refraction in E Region during sporadic E events. | Free Space Loss, reflection loss. | 2E, nominally 2,400km (1,900 – 2,800km) |
| 5 | Skywave | Ionospheric reflected & refraction in F Region enhanced by solar radiation. Splits to F1 and F2 layers diurnally. A function of Maximum Usable Frequency. | Free Space Loss, entry/exit losses, reflection loss. | 1F, 2F and occasionally higher orders (1F1, 2F1, 1F2, 2F2 etc.). Distance 100km to 6,000km. Rarely, complex modes like 1F1Es1F1. |
Thinking about propagation modes
Many radio amateurs get it wrong. They claim auroral communications when they are pointing at each other, instead of north to the aurora. They claim it’s sporadic E over a 500km path when tropospheric diffraction is more likely. And they claim aircraft scatter, when the geometry would likely preclude reflection from an airplane.
All is understandable.
Radio amateurs need to think critically about the propagation mode over a particular path. Each propagation mode has uniqueness. It’s that uniqueness that identifies which propagation mode is active – remembering of course that it could even be multiple modes simultaneously. Radio amateurs need to think which mode is most likely.