RTK dropouts near power lines or cell towers? Anti-jamming receivers for AgOpenGPS (F9P vs Septentrio AIM+)

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I’m from UAV GNSS (uav-gnss.com) — we build Septentrio-powered RTK receivers, and a lot of our customers run AgOpenGPS. I’ve been reading this forum for a while and a recurring theme keeps showing up: random RTK dropouts near sheds, solar arrays, power lines, and cell towers. Since the ZED-F9P is the default receiver around here, I wanted to share what’s actually happening and what the options are.

Why the F9P drops fix near interference

GNSS signals arrive at the surface at extremely low power — roughly equivalent to a 20 W light bulb viewed from 20,000 km. Any nearby RF source can overwhelm them:

  • Solar inverters and power lines (broadband harmonics — increasingly common on farms)
  • 4G/5G towers and co-located radios
  • Grain dryers, electric fences, VHF/UHF transmitters
  • Co-located antennas on the same machine (radio, camera, Wi-Fi)

The ZED-F9P has roughly 25 dB of jamming immunity in typical configurations. Near moderate interference that shows up as: loss of RTK fix, longer re-convergence (10-45 s), or meter-level drift before recovery — all things that ruin a pass line.

What actually helps

  1. Antenna placement — free, and often 80% of the fix. Keep the antenna away from cab radios, inverters, and wiring. A proper survey-grade antenna with a ground plane also improves multipath rejection.
  2. A receiver with real anti-jamming — Septentrio mosaic modules include AIM+ (Advanced Interference Mitigation): roughly 60 dB of jamming immunity versus ~25 dB on the F9P. In practice that means holding fixed RTK even when driving directly past a 5G tower or under high-voltage lines.
  3. Base station location — the base is just as exposed as the rover. If your base sits near a shed with solar inverters, you’re injecting interference into every rover on the farm.

Field test — power-line corridor

  • ZED-F9P: dropped to float/single within ~3 m of the line, 40+ s to re-converge
  • EV322 (mosaic-X5, AIM+): held fixed RTK for the entire pass

For AgOpenGPS specifically

Our receivers output standard NMEA over UART/USB and accept RTCM in, so the AgOpenGPS config doesn’t change — same serial port, same $GGA/$RMC parsing. A few AOG builders also use our dual-antenna heading module (HB51) to get heading without a separate IMU, which is handy for implement guidance.

If this is useful I’m happy to answer technical questions in the thread — and I’d genuinely like to hear what other people have tried for interference-related dropouts, F9P or otherwise.

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