Passive GNSS Interference Monitoring

[Pavel]

Short answer: Monitor GNSS bands passively with a protected antenna path, calibrated spectrum or I/Q metrics and independent receiver observables. A rise in power alone does not identify source, intent or spoofing; record evidence and uncertainty without transmitting.

Before you start​

• Keep GNSS and drone work passive unless the experiment has explicit authorization and an RF-controlled environment; do not jam, spoof or interfere with navigation or aircraft.
• Record receiver clock, antenna, gain, sample rate, observation location precision and ground truth before interpreting anomalies.

Step-by-step method​

1. Step 1: Define GNSS band, normal baseline, time resolution and alarm metrics such as in-band power, AGC change, carrier-to-noise loss or correlation distortion.
2. Step 2: Use an appropriate GNSS antenna and filtered path, and verify the monitoring receiver remains linear near cellular and other strong signals.
3. Step 3: Record spectrum/IQ, timestamps and trusted GNSS receiver status simultaneously. Mark local equipment changes and antenna faults.
4. Step 4: When an anomaly occurs, compare multiple sensors or locations at a privacy-safe precision and preserve raw data for authorized analysis.

Concrete example​

A broadband power increase plus falling C/N0 across many satellites supports an interference event, but a loose antenna connector can create similar receiver symptoms without a power rise. Combine observables.

How to judge the result​

A useful monitor detects controlled test events, has a measured false-alarm baseline and reports anomalies without making unsupported attribution claims.

What to record​

• Separate frequency-reference accuracy from absolute time alignment: 10 MHz disciplines frequency while PPS marks a time boundary.
• Use multiple independent observables for GNSS interference or spoofing claims, such as spectrum, AGC behavior, correlation, navigation consistency and trusted reference data.
• For direction finding or RF classification, report uncertainty and test across channels, distances, devices and temperatures.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Publishing a map with exact sensitive receiver coordinates can create privacy or security risks unrelated to the research objective.

Final check​

Repeat the passive observation against an independent trusted reference and state uncertainty. Do not make spoofing, interference or aircraft claims from a single receiver screenshot.