EIRP Explained: Satellite Signal Strength on Earth
EIRP sounds like jargon, but it is the single number that tells you how big a dish you need. Short for Effective Isotropic Radiated Power, it describes how strong the satellite's signal is where you live.
What EIRP Means
EIRP combines the satellite's transmit power and the size of its broadcast antenna into one effective number, measured in dBW. A higher EIRP means a stronger signal on the ground — and therefore a smaller dish.
Why It Varies by Location
A satellite does not shine equally everywhere. Its broadcast antenna shapes the signal into a “footprint” that is strongest over its target region and weaker at the edges. EIRP maps that strength geographically.
Reading an EIRP Map
Satellite operators publish EIRP contour maps. The inner contour (highest EIRP) may need only a 45 cm dish; the outer contour may need 90 cm. If you live on the edge, plan for the larger dish.
How EIRP Drives Your Dish Size
- High EIRP centre: 60 cm dish is plenty.
- Medium EIRP: 80 cm.
- Low EIRP edge: 90 cm or more.
This is why two neighbours with the same satellite sometimes need different dishes — they are at different points on the footprint.
EIRP and Rain Margin
Even within a decent EIRP contour, you want a dish slightly bigger than the minimum. The extra size buys you rain fade margin that the raw EIRP number does not give you.
Where to Find It
Look up your target satellite on a satellite footprint map. The EIRP contours are usually marked in dBW. Compare your location to the contour lines.
EIRP is the satellite's ground-level signal strength. Check it before you buy the dish — it tells you exactly what size you need.
