How to Read a Propagation Heatmap
If you've ever wondered "which band should I even try right now?", a propagation heatmap answers that question with actual data instead of guesswork. Rather than predicting propagation from solar numbers alone, a heatmap shows you what has genuinely been heard, band by band, hour by hour.
What a Propagation Heatmap Actually Shows
A typical HF propagation heatmap is a grid: bands on one axis, time of day (usually UTC) on the other. Each cell is colored by how much activity was recorded for that band during that hour, often broken down further by day of the week.
The data behind it comes from real reception reports, most commonly from automated systems like PSK Reporter, which collects spots from thousands of receiving stations worldwide reporting decoded digital signals (like FT8) along with the exact time and band.
Why Hour and Day Matter
Propagation isn't static. It shifts throughout the day as the ionosphere changes with sunlight, and it also shifts by season and by the current point in the solar cycle. A few patterns that show up consistently in heatmap data:
- Lower bands (80m, 40m) tend to open up in the evening and overnight, once D-layer absorption drops off.
- Higher bands (15m, 12m, 10m) are usually strongest during daylight hours, especially mid-morning to afternoon.
- 20m is often the most consistently active band across a wide part of the day, which is why it shows up so often in heatmaps as a reliable "safe bet."
Seeing these patterns laid out visually, instead of having to remember them, is the main value of a heatmap: you can glance at the current hour's column and immediately see which bands have historically been productive.
Heatmaps vs. Solar Indices
It's worth understanding the difference between a heatmap and the solar indices you'll see quoted elsewhere (SFI, K-index, A-index):
| Metric | What it tells you |
|---|---|
| SFI (Solar Flux Index) | General solar activity level, higher usually means better high-band conditions |
| K-index | Short-term geomagnetic disturbance, high values often mean degraded HF conditions |
| A-index | A longer-window average of geomagnetic activity |
| Propagation heatmap | Actual observed activity by band and hour, based on real spots |
Solar indices are predictive and abstract. A heatmap is descriptive and concrete: it shows you what has actually been happening, which is often more useful for deciding what to try right now.
How to Use a Heatmap Before Getting on the Air
- Check the current UTC hour and day of week on the heatmap.
- Look for the band (or bands) with the strongest activity in that column.
- Cross-check with the live DX cluster feed to see what's actually being spotted on those bands right now.
- If you're chasing a specific region, look for patterns at that particular hour rather than relying on a single day's snapshot.
A Note on Data Sources
Heatmaps are only as good as the underlying spot data. Automated sources like PSK Reporter capture a huge volume of real-world activity, but they're naturally biased toward digital modes and toward regions with more active receiving stations. Treat a heatmap as a strong statistical guide, not an absolute guarantee, for any single moment.