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GPS Debug Reference

Reference for interpreting output from debug_gps_ublox.py (u-blox modules only). The GPS module handles all satellite selection and fix decisions automatically - these values reflect module state, not configurable settings.

Run the script on the Streamer: 

v3xctrl-python -m v3xctrl_telemetry.apps.debug_gps_ublox

Tip: If satellite acquisition is slow during diagnosis, stop video streaming. LTE transmission can interfere with GPS reception at the L1 frequency (1575 MHz).

Reports the current position fix, satellite count, coordinates, and speed.

Fix Type

Fix Type Meaning
No Fix No position fix - normal during cold start (up to 60s)
Dead Reckoning Position estimated from motion sensors; no GNSS signal available
2D Fix Horizontal position only - altitude not determined
3D Fix Full position fix - normal outdoor operation
GNSS+Dead Reckoning GNSS combined with motion sensor data
Time Only Time synchronized but no position fix

Expected: 3D Fix in open sky. No Fix is normal during cold start (up to 60s). Weak signal, jamming, or obstructions can significantly delay acquisition.

Satellite Count (satellites)

Count Assessment
0 No satellites - antenna issue, obstruction, or reset
1-3 Weak - fix may be lost or inaccurate
4-6 Good - stable 3D fix expected outdoors
7+ Excellent

Warning threshold: Drop of 2 or more satellites in one cycle is flagged.

Per-satellite signal data for all satellites the module can see. Satellites are grouped as used: (actively contributing to the position fix), seen: (visible but not used), and unhealthy: (flagged by the module as unreliable and excluded from position calculation). The module supports GPS, SBAS, Galileo, BeiDou, IMES, QZSS, and GLONASS, and can track up to 3 systems simultaneously.

Signal Strength (CN0, dBHz)

Carrier-to-noise density ratio per satellite. Higher is better.

CN0 (dBHz) Assessment
< 20 Very weak - unusable
20-25 Poor - may not contribute to fix
25-30 Marginal
30-35 Good
35-45 Excellent - clear sky view
> 45 Outstanding

Warning threshold: < 25 dBHz for a satellite actively used in the nav solution.

Minimum to decode navigation data from a satellite: ~32 dBHz.

MON-RF - RF Monitor

Antenna status and RF interference data reported by the module.

Antenna Status

Expected: OK power=On - antenna connected and powered. Short or Open indicate a hardware problem - check the connector and cable. Unknown is normal for passive antennas (the module cannot detect passive antenna presence). Initializing appears briefly on startup.

Jamming Indicator

Continuous-wave jamming indicator. Scale: 0-255.

jamming Assessment
0-20 No jamming
21-50 Low - likely normal variation
51-100 Elevated - possible interference nearby
101+ High - likely active jamming or strong interference

Warning threshold: > 50.

The module also reports a jamming state: OK means no jamming detected, Warning means jamming detected, Critical means strong jamming - position may be unreliable. Unknown means jamming detection is not available on this module.

Note: This indicator responds to narrow-band (CW) interference only.

Gain

Automatic gain control counter (scale: 0-8191). Reflects the receiver's gain adjustment to maintain signal levels. The baseline varies depending on antenna type, placement, and environment, so there is no universal threshold. Watch for sudden changes rather than absolute values.

  • Stable - normal RF environment
  • Sudden drop - increased noise floor, possible wideband interference
  • Very low - strong signal or close jamming source

Noise per ms

Background RF noise measurement.

noise Assessment
80-120 Normal outdoor environment
> 150 Elevated noise - possible interference
> 200 High noise - likely RF issues nearby

Typical Healthy Output (open sky, 3D fix)

Each satellite in the used: and unhealthy: groups is shown as {SYSTEM}{ID}({CN0}dBHz {elevation}°). For example, GPS1(38dBHz 55°) is GPS satellite 1 with a signal strength of 38 dBHz at 55° above the horizon. Higher elevation generally means better signal.

[16:11:06.064] POSITION [NAV-PVT]  fix=3D Fix  satellites=7  lat=48.123456  lon=11.567890  speed=0.0 km/h
[16:11:06.116] SATELLITES [NAV-SAT]  7 used / 24 visible
               used:        GPS1(38dBHz 55°)  GPS3(32dBHz 22°)  GAL5(36dBHz 41°)  ...
               seen:        17 satellites
[16:11:06.245] RF-STATUS [MON-RF]  antenna=OK power=On jamming=4/255 state=OK gain=8190 noise=98

Typical Output During Satellite Drop

[16:11:05.064] POSITION [NAV-PVT]  fix=3D Fix  satellites=4  lat=48.123456  lon=11.567890  speed=1.2 km/h
[16:11:06.064] POSITION [NAV-PVT]  fix=No Fix  satellites=0  lat=--  lon=--  speed=--
[WARN] satellites dropped 4 -> 0
[16:11:06.116] SATELLITES [NAV-SAT]  0 used / 0 visible
               used:        (none)
[16:11:06.245] RF-STATUS [MON-RF]  antenna=OK power=On jamming=5/255 state=OK gain=8190 noise=100

If antenna=OK and jamming is low during a drop, the cause is likely signal obstruction, LTE interference, or a brief module reset - not an antenna or RF hardware problem.

Warnings

All warnings are prefixed with [WARN].

Warning Meaning
satellites dropped N -> M Satellite count dropped by 2 or more in one cycle
N used satellite(s) below signal threshold (25dBHz) N satellites used for position have weak CN0
No fix - strongest visible satellite only NdBHz, below acquisition threshold (25dBHz) for ephemeris/almanac data No fix and visible satellites too weak to download navigation data
Antenna status: Short/Open Hardware problem - check connector and cable
Jamming indicator high: N/255 Jamming indicator above threshold (50)
Jamming state: Warning/Critical Module flagged active jamming
unexpected fixType=N Unknown fix type reported by module

For full protocol details, see the u-blox M10 Interface Description.