Introduction
GNSS signals travel 20,000 km from space. By the time they reach you, they're incredibly weak, weaker than a single photon from a 25-watt light bulb at the same distance. Many things can interfere with them.
#1: The Ionosphere (Biggest Error Source)
- Layer of charged particles 60–1000 km up
- Slows and bends signals
- Error: 2–10 meters
- Worse near equator and during solar storms
- Fix: Dual-frequency receivers or SBAS corrections
#2: Multipath (The Urban Problem)
- Signal bounces off buildings/ground before reaching you
- Reflected path is longer → receiver thinks it's farther
- Error: 1–10+ meters
- Worst in urban canyons, near water
- Fix: Move away from reflective surfaces, better antennas
#3: Troposphere (Weather Effects)
- Lowest atmospheric layer (0–18 km)
- Water vapor and pressure slow signals
- Error: 0.5–2 meters
- Affects vertical accuracy more
- Fix: Models and differential techniques
#4: Satellite Geometry (DOP)
- Not interference, but multiplies other errors
- Clustered satellites = poor geometry = larger errors
- Fix: Wait for better geometry, use multi-GNSS
#5: Obscuration (Blocked Signals)
- Buildings, trees, terrain physically block signals
- Complete loss indoors
- Fix: Move to open sky, external antenna
Bonus: Human-Made Interference
- Jamming: Illegal devices that overpower GNSS
- Spoofing: Fake signals tricking receivers
- Unintentional: Other electronics emitting noise
Vital Points
- Ionosphere is largest error source for single-frequency users
- Multipath causes big errors in cities, move to fix it
- Satellite geometry multiplies all errors
- Physical blocking is obvious but often overlooked