What does the propagation heatmap show?

The heatmap displays which Maidenhead grid squares are within radio line-of-sight of a satellite during a specific pass. Brighter colours indicate higher maximum elevation (stronger signal). This helps operators find other stations who can hear the same pass and coordinate contacts.

How is the coverage footprint calculated?

For each pass, the satellite's position is propagated using SGP4 at 30-second intervals. At each point, the ground footprint is computed using the satellite's altitude and a minimum elevation angle of 5°. Grid squares within this footprint are coloured based on the peak elevation they experience during the pass.

Can I use this for contest planning?

Yes — the heatmap is ideal for satellite contest planning. You can see which grid squares are workable on each pass, identify rare grids in the footprint, and time your operating schedule to maximise unique grid contacts. The overlap view shows when multiple operators in different grids can hear the same satellite simultaneously.

What amateur radio frequencies do satellites use?

Most amateur radio satellites operate in the VHF (144–148 MHz) and UHF (430–440 MHz) bands. FM repeater satellites like SO-50 and the ISS use FM on these frequencies. SSB/CW linear transponders on satellites like FO-29 and RS-44 allow multi-mode contacts. Some satellites also use 10 GHz microwave bands.

How do I find my Maidenhead grid square?

Enter your city, postcode, or coordinates in the amateur radio pass predictor and it computes your 6-character Maidenhead grid locator automatically. You can also use the grid search tool on this page to check if your grid is within a satellite's coverage footprint.

Satellite Propagation Heatmap — Grid Coverage

Understanding Satellite Propagation & Coverage

How Satellite Coverage Works

A satellite's coverage footprint is the area on the ground from which it can be seen above a minimum elevation angle. For a typical LEO satellite at 400 km altitude, the footprint is a circle roughly 5,000 km in diameter (at 0° minimum elevation). At a more practical 10° minimum elevation — where signals are strong enough for reliable communication — the footprint shrinks to about 3,600 km diameter.

Why Grid Squares Matter

The Maidenhead grid square system divides the Earth into a hierarchy of rectangles. A 4-character grid (e.g. IO91) covers roughly 100 × 200 km. A 6-character subsquare (e.g. IO91wm) covers about 5 × 10 km. For satellite work, 4-character grids are the standard exchange — they give enough precision to confirm that two stations shared the same pass while being short enough to transmit quickly during a brief satellite window.

Using the Heatmap

Select a satellite and pass from the controls above, then click "Compute Coverage". The heatmap shows every grid square that can see the satellite during the pass, colour-coded by maximum elevation — brighter colours indicate stronger potential signals. Use this to find operators in other grids who could hear the same pass and coordinate contacts in advance.

Contest & DX Planning

For satellite contests (AMSAT Field Day, ARRL VHF+), the heatmap is invaluable for planning. Identify which passes cover rare grid squares, find time windows where multiple high-value grids overlap with your own footprint, and prioritise passes that give you access to grids you haven't worked yet. The grid search tool below the map tells you instantly whether a specific grid is workable on a given pass.

For pass predictions with Doppler-corrected frequencies, visit the ham radio pass predictor. Listen to recordings from other operators in the audio archive. Learn more about orbital mechanics in the Orbital Academy.