StratuxADS-B ground stations and coverage
An ADS-B ground station is an FAA radio site that listens to aircraft ADS-B Out for air traffic control and broadcasts weather and relayed traffic back to ADS-B In receivers. What you receive depends on line of sight to a station, the altitude tier that station serves and, for relayed traffic, radar coverage.
The FAA's published list has 655 stations, and every one is on our ADS-B ground station map. Here's what those dots mean for your flight.
What a ground station does
Each site does several jobs (AIM 4-5-7 to 4-5-10):
- Receives ADS-B Out from aircraft and passes it to ATC.
- Broadcasts FIS-B weather and airspace data on 978 MHz to anyone in range. See FIS-B explained.
- Broadcasts TIS-B, radar traffic for client aircraft, on both 978 and 1090 MHz.
- Broadcasts ADS-R, which copies ADS-B Out from one frequency to the other. See TIS-B and ADS-R.
The FAA notes ground stations are "smaller and more adaptable than radar towers," so they can go where radar can't (FAA Ins and Outs).
How many stations, and where
Our map uses the FAA's list of ground stations as of August 31, 2018, released through the FAA's FOIA reading room. It has 655 stations, including a few in Mexico, the Caribbean and the Pacific. We haven't found a newer FAA list. Details and the original PDF are on the about the map page.
Canada's 978 MHz stations are run by the volunteer CIFIB network and show in red. Check cifib.ca for their newest sites. More on that in Stratux in Canada and outside the US.
Altitude tiers set who a station serves
The FAA assigns each UAT station to one of four altitude tiers (AC 00-63B, Appendix A, Figure A-2):
| Tier | Altitude range | Built for |
|---|---|---|
| High | surface to FL240, best from about 9,100 ft AGL | turbocharged and turbine GA en route |
| Medium | surface to 14,000 ft AGL, best from about 2,200 ft AGL | most GA en route |
| Low | surface to 3,000 ft AGL | the terminal area |
| Surface | the surface | aircraft "in the immediate vicinity of major airports" |
The tier also decides which FIS-B products a station sends and how far ahead they reach. A high-tier station sends regional radar out to 250 nm. A low-tier station sends it out to 150 nm. The full table is on the FIS-B page.
How much of the country that covers, per Garmin's GTN Xi pilot's guide (190-02327-03 Rev. G, p. 5-38):
- Surface: FIS-B on the ground at about 36 major US airports. The 2018 FAA list on our map has only 5 Surface-tier radios, at 3 airports, so surface coverage at those airports comes from more than the Surface-tier radios.
- Terminal: below 3,000 ft AGL near about 235 airports.
- Airborne: much of the US at 3,000 ft AGL and above.
Line of sight: why altitude matters
ADS-B is a line-of-sight radio link. Hills, buildings and the curve of the earth block it. FIS-B "reception is line-of-sight within the service volume of the ground infrastructure" (AIM 4-5-9).
The standard radio horizon formula gives the farthest a direct signal can reach over flat ground. In nautical miles, it's 1.23 × (√ station antenna height + √ your height), with heights in feet (ATIS Telecom Glossary, radio horizon range).
FAA stations don't all have the same antenna height. To show the shape of it, here's the math for a station antenna 100 ft up:
| Your height above the ground | Radio horizon to that station |
|---|---|
| 5 ft (on the ramp, flat open ground) | about 15 nm |
| 1,000 ft | about 51 nm |
| 3,000 ft | about 80 nm |
| 5,500 ft | about 104 nm |
| 10,000 ft | about 135 nm |
Those are best-case numbers. Real range won't be that good. Terrain, hangars, trees, your antenna's spot in the cockpit and the station's transmit power all cut it down. On the ramp, one hangar between you and the station can block it completely. That's why no weather on the ground is normal at most fields (see no weather or traffic).
Notice how fast range grows with the first thousand feet. Most of the gain comes early in the climb.
What each service needs from coverage
- Direct air-to-air traffic needs no ground station at all. Your receiver hears any ADS-B Out aircraft in radio range on the frequencies it covers.
- FIS-B weather needs line of sight to one station. The FAA's required ceiling is FL240, with reception expected above it (FAA pilot page).
- TIS-B needs a station set up for TIS-B, plus radar that can see the target. The AIM says radar siting can limit TIS-B at low altitudes near some airports. If radar can't see a target, it won't come through as TIS-B.
- TIS-B and ADS-R are available at or below FL240, and only for client aircraft with qualifying ADS-B Out. Without your own Out, you see what's built for clients nearby. The TIS-B and ADS-R page explains why.
Reading the ground station map
The map shows every station on the FAA list and the CIFIB network, colored by tier. You can download the station list as a CSV (ID, city, state or province, latitude, longitude, tier).
A few tips for using it:
- It's a map of stations. Coverage depends on your altitude and the terrain, so there's no single footprint to draw.
- Look at tier, not just distance. A surface or low-tier station near your field helps in the pattern. High-tier stations matter en route.
- Mountain fields are harder. Terrain between you and the nearest station can push weather well up the climb.
Flight-tracking sites show something different. Their maps plot aircraft, much of it heard by volunteer feeders. They aren't a map of FAA ground-station coverage.
Which stations is your receiver hearing?
On a Stratux, open the web interface at 192.168.10.1:
- Status page. The Towers count in the UAT Statistics rows is the number of ground stations heard.
- Towers page. Lists each station heard in the last minute, with its position, signal strength and message count.
Every station sends its own position, so you can match what you hear to the map. Spot a station that isn't on our map, or one in the wrong place? Tell us and we'll check it and add it.
Where ADS-B Out is required
Ground stations also serve the ADS-B Out rule, 14 CFR 91.225. Here's the airspace it lists (14 CFR 91.225):
- Class A: 1090ES only.
- Class B and C, and the airspace above them up to 10,000 ft MSL.
- The 30 nm Mode C veil, from the surface up to 10,000 ft MSL. The rule has a few exceptions here.
- Class E at and above 10,000 ft MSL in the 48 states and DC, excluding the airspace at and below 2,500 ft above the surface.
- Class E over the Gulf at and above 3,000 ft MSL, within 12 nm of the coast.
Below Class A, either 1090ES or 978 MHz UAT meets the rule.
The rule only covers ADS-B Out. ADS-B In is optional, and it's what puts the weather and traffic on your screen. The how ADS-B works guide has the airspace diagram.
Frequently asked questions
What is an ADS-B ground station?
An FAA radio site that receives ADS-B Out for air traffic control. It also broadcasts FIS-B weather, TIS-B traffic and ADS-R rebroadcasts to ADS-B In receivers in line of sight.
Is there an ADS-B coverage map?
The Stratux ground station map shows every station on the FAA's published list, plus Canadian CIFIB stations, colored by altitude tier. It shows where stations are, not an exact coverage footprint, because real range depends on your altitude and the terrain.
Why do I get ADS-B weather in the air but not on the ground?
Ground stations are line of sight. On the ramp, hangars, terrain and a low antenna usually block them. Climbing raises your radio horizon and clears those. Surface radios near some major airports are there to serve aircraft on the ground.
Do I need a ground station to see traffic?
Not for aircraft broadcasting ADS-B Out. Your receiver hears those directly, air to air. Ground stations are only needed for relayed TIS-B and ADS-R traffic, and for FIS-B weather.
Want to see how coverage fits together? Signal Path has you place towers to work out how coverage, FIS-B, TIS-B and ADS-R fit together, and Tower Hunt has you log real FAA stations.