# Propagation modes

Radio hams frequently jump to conclusions about propagation modes. It’s no surprise. Propagation is complex and a little knowledge can lead to assumptions. This page attempts to give a logic to understanding how far signals can go for a given frequency, time of day and station characteristics. It aims to describe propagation modes, and in so doing, give understanding of propagation range limits.

This page is not intended to be definitive, all knowing, giving a master framework. It will be worked on over the coming years and maybe will ultimately give that. But for now, it’s a guide.

## 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 path 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.

Signals can propagate in the troposphere, or they can go up to the ionosphere and be refracted, turned, back to Earth.

In the troposphere, signals propagate by ground wave and space wave. Paths are frequently obstructed by terrain and land use features like buildings and trees, so generally, propagation is by diffraction.

At LF and HF, the idea of a space wave is difficult since the Fresnel zone is huge. Instead, signals hug the ground, and the path length is lengthened by the undulation. At VHF and UHF, ground wave is attenuated, and space wave prevails.

At HF and lower VHF, propagation can be by sky wave.

## Ground, space and sky all at once

So, you might think, and indeed want, skywave (for example), but you’ll get all the rest too to varying extent.

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 four) groupings: