Propagation prediction tools

What it is

Propagation tools help you decide which band to try and when, instead of tuning around hoping. They fall into three families, which answer different questions. This article describes the categories, not any one product: features and availability change, so check each tool's own documentation.

Three kinds of tool

Kind	Answers	Typical examples
Space weather data	How active is the sun, and how disturbed is Earth's magnetic field?	solar flux, A and K indices, X-ray and solar wind readings, published by space-weather agencies
Prediction models	Between these two places at this time, which frequencies should work?	HF prediction programs (many built on the VOACAP engine), usually run on your computer or on a website
Live reports	What is actually being heard right now?	maps built from spotting networks, beacons and WSPR

For VHF and UHF, the idea is the same, but the inputs are weather rather than the sun: forecasts that show where tropospheric ducting is likely, and Sporadic E or Aurora propagation alerts. See Tropospheric ducting and scatter.

Reading the numbers

Space weather data are inputs, not answers. In general, a higher solar flux means stronger ionisation and better support for the higher HF bands, while a high K or A index means a disturbed field and degraded paths, especially near the poles. The solar cycle and propagation indices explains each one, and Space weather explains what drives them.

A prediction model takes a path, a date and time, transmit power, antennas and a smoothed sunspot figure, and returns an estimate of the MUF (see MUF, LUF and the best frequency) and the likelihood a signal will get through. Predictions are statistical: they describe a typical day in that month, not today.

Using them together

1. Plan with a prediction: which band and hour look promising for the place you want to reach?
2. Check the sun: is anything disturbing the field today?
3. Look at live reports: are stations from that region being heard on that band now?
4. Decide by listening. A real signal on the band outranks any chart.

When a forecast and a live report disagree, believe the live report: it is the measurement, while the forecast is an average.

Related

• The solar cycle and propagation indicesSunspots, solar flux, and the A and K indices.
• MUF, LUF and the best frequencyThe highest and lowest usable frequencies for a path.
• Space weatherFlares, CMEs and storms, and how they help or wreck HF.
• DX clusters, RBN and PSK ReporterFinding activity.
• Skywave, hops and the skip zoneHow HF signals return to Earth hundreds or thousands of miles away.
• The ionosphereThe D, E and F layers: what they are and what they do to radio waves.