Is your receiver being jammed, spoofed, or just experiencing a bad sky view? Learn the exact C/N0 thresholds, position anomalies, and monitoring tools that separate a technical glitch from a deliberate electronic attack.
Key Metric: C/N0 (Carrier-to-Noise Density)
The single most useful number is C/N0, also called CNR, measured in dB-Hz. Healthy GNSS tracks around 30–45 dB-Hz. Watch for:
- A simultaneous drop across all satellites to below ~25 dB-Hz — a classic jamming signature.
- A sharp noise-floor rise with CNR collapse — interference entering the front end.
- All satellites showing improbably high, uniform CNR — possible spoofing.
Jamming Indicators
- Sudden loss of fix across multiple receivers in the same location.
- CNR drops on every satellite at once (not just one or two).
- Position freezes or jumps to 0,0 while the platform moves.
- Interference appears only in specific spots or time windows.
Spoofing Indicators
- Position or time drifts smoothly away from truth.
- Reported altitude/speed inconsistent with the platform.
- Time jumps that break logging, encryption, or timing systems.
- Constellation inconsistency: GPS and Galileo disagree on position.
Detection Tools
| Tool | What it reveals | Best for |
|---|---|---|
| Spectrum analyzer | Out-of-band / in-band noise, jammer frequency | Forensics, siting |
| RF monitor / interference detector | Continuous CNR and anomaly alarms | Fixed sites, vehicles |
| Protected receiver with threat reporting | Built-in nulling status and spoof flags | Operational platforms |
| Multi-sensor fusion (INS/odometry) | Inconsistency between GNSS and motion | Spoofing catch |
Building a Monitoring Architecture
For critical sites, log CNR and fix status continuously and correlate outages with location and schedule. A practical layered setup:
| Layer | Component | Function |
|---|---|---|
| RF | Spectrum / RF monitor | Detect noise and jammers |
| Receiver | Protected GNSS receiver | Null jamming, flag spoofing |
| Cross-check | INS / odometry | Validate position integrity |
| Logging | Time-series store | Evidence and trend analysis |
Public interference maps help confirm regional patterns, but on-site logging is the only reliable evidence.
From Detection to Protection
Detection tells you the threat is real; only hardware stops it. A CRPA antenna with adaptive nulling rejects jamming at the front end, while authentication and sensor fusion defeat spoofing. See our protection hardware or talk to our team about a monitoring-and-mitigation setup.
FAQ
Q: Can my phone detect jamming?
A: Consumer phones rarely expose C/N0 or threat data. Specialized receivers or RF scanners are needed.
Q: What CNR drop indicates jamming?
A: A simultaneous drop across all satellites, especially with a rising noise floor, is the strongest indicator.
Q: Is detection enough without mitigation?
A: No. Detection alerts you, but only nulling and anti-spoofing hardware restores trustworthy positioning.