RTK Fixed Solution Keeps Dropping to Float? Troubleshooting Guide
When RTK repeatedly drops from Fixed back to Float instead of holding a stable solution, six causes are typically responsible: multipath interference from nearby reflective surfaces, weak satellite geometry (poor DOP), intermittent radio link dropouts between base and rover, obstructed sky view from trees or structures, antenna cable or connection issues, or an aging/degraded base station correction signal. Unlike a gradual accuracy drift, Fixed-to-Float cycling usually points to an intermittent, not constant, disruption — making the timing and pattern of drops the key diagnostic clue.
- 1. Fixed-to-Float Cycling vs Accuracy Drift: What's the Difference
- 2. Problem 1: Multipath Interference
- 3. Problem 2: Weak Satellite Geometry (High DOP)
- 4. Problem 3: Intermittent Radio Link Dropouts
- 5. Problem 4: Obstructed Sky View
- 6. Problem 5: Antenna Cable or Connection Issues
- 7. Problem 6: Degraded Base Station Correction Signal
- 8. Quick Reference Diagnosis Table
- 9. FAQ
1. Fixed-to-Float Cycling vs Accuracy Drift: What's the Difference
Understanding the distinction between accuracy drift and Fixed-to-Float cycling is essential for rapid troubleshooting. Accuracy drift occurs when the receiver maintains a continuous "Fixed" solution status, but the coordinate values slowly drift or bias away from true positions due to atmospheric or baseline conditions (covered in our Why Is My RTK Accuracy Dropping guide).
In contrast, Fixed-to-Float cycling is characterized by the solution status repeatedly breaking and recovering between Fixed and Float. This behavior almost always points to an intermittent physical or environmental disruption rather than a persistent background error.
To diagnose the root cause, observe your data collector status bar and record the exact timestamps, locations, and surrounding environmental triggers (such as moving near structures, vegetation, or passing machinery) whenever a drop occurs.
2. Problem 1: Multipath Interference
Symptom: Fixed status drops frequently when operating near buildings, large metal structures, standing water surfaces, or parked vehicles.
Cause: GNSS satellite signals reflect off nearby surfaces before reaching the receiver antenna, creating false pseudo-range measurements and corrupting integer ambiguity resolution.
Fix: Avoid prolonged stationary work directly adjacent to high-reflectivity barriers; full-constellation 1408-channel receivers can leverage advanced tracking to filter out a higher volume of erroneous signals; relocate to an open-sky position if re-initialization fails.
3. Problem 2: Weak Satellite Geometry (High DOP)
Symptom: The Fixed solution becomes difficult to maintain during specific windows of the day, even under an apparently clear open sky.
Cause: Visible satellites cluster within a narrow sector of the sky rather than maintaining a balanced spatial distribution, causing dilution of precision (DOP) values to spike.
Fix: Monitor real-time DOP parameters in your field software; pause precision layout work if PDOP values persistently exceed 6; utilizing a multi-constellation receiver (GPS, BDS, GLONASS, Galileo) substantially mitigates geometrical clustering.
4. Problem 3: Intermittent Radio Link Dropouts
Symptom: The rover drops from Fixed to Float intermittently while running a Base+Rover configuration, while network NTRIP RTK modes remain unaffected.
Cause: UHF or LoRa data links are temporarily blocked by terrain changes, undulating ground profiles, or transient physical obstacles like moving trucks and heavy machinery.
Fix: Inspect the base station placement to ensure unobstructed line-of-sight across the survey zone; for comprehensive radio diagnosis steps, review our Base and Rover Radio Not Connecting Troubleshooting Guide.
5. Problem 4: Obstructed Sky View
Symptom: Solution status fluctuates continuously when moving close to dense tree canopies, narrow urban corridors, or steep rock cuts.
Cause: Physical blockage of satellite signals drops the active satellite count below the critical redundancy threshold required for integer ambiguity resolution.
Fix: Plan survey paths to maintain optimal sky visibility; if constrained environments are unavoidable, allow extended initialization periods or switch to post-processed kinematic (PPK) workflows.
6. Problem 5: Antenna Cable or Connection Issues
Symptom: Status drops occur randomly with no apparent correlation to environmental obstacles or open-sky conditions.
Cause: Loose antenna ports, degraded external antenna cables, or oxidized coaxial connectors introducing intermittent signal attenuation.
Fix: Verify that all antenna connectors are firmly tightened; routinely inspect external cabling for physical wear or micro-cracks (common on controller setups like the TS8i Pro); replace damaged cables with manufacturer-certified replacements.
7. Problem 6: Degraded Base Station Correction Signal
Symptom: Fixed stability deteriorates progressively after several hours of continuous multi-hour layout tasks.
Cause: Base station internal battery discharge reducing transmission output power, or environmental shifts altering the base's satellite tracking environment.
Fix: Monitor base power levels regularly — the MAX5 base station houses a 13,200mAh battery rated for over 8 hours of continuous uptime; verify that the base setup site remains entirely free of newly introduced physical obstructions.
8. Quick Reference Diagnosis Table
| Symptom | Root Cause | First Action |
|---|---|---|
| Drops near buildings/water/vehicles | Multipath interference | Move to open area, re-initialize |
| Drops at specific times, open sky | Weak satellite geometry | Check PDOP value, pause if high |
| Drops intermittently, Base+Rover mode | Radio link dropouts | Check for line-of-sight obstruction |
| Drops near trees/canyons/structures | Obstructed sky view | Choose open-sky path, extend init time |
| Drops with no environmental pattern | Antenna cable/connection | Check antenna connection, replace cable |
| Degrades gradually over hours | Degraded base signal | Check base battery level and position |
9. FAQ
What's the difference between Fixed dropping to Float and gradual accuracy drift?
Fixed dropping to Float involves the receiver's solution status repeatedly cycling between integer ambiguity resolution states due to transient interference or signal blockages. Gradual accuracy drift occurs when the receiver stays stably in Fixed status, but absolute coordinates wander away from true positions over time.
How can I tell if multipath is causing my Fixed status to drop?
Multipath interference is highly localized. If your RTK solution drops to Float consistently whenever you approach large metallic objects, glass facades, water bodies, or moving vehicles, and immediately recovers once you step away into an open area, multipath reflection is the primary culprit.
What PDOP value should trigger concern during RTK survey?
A Position Dilution of Precision (PDOP) value under 3 is considered excellent for high-precision GNSS work. When PDOP climbs above 6, satellite geometry is poor enough that maintaining a stable Fixed solution becomes difficult, and precision measurements should be paused until constellation geometry improves.
Does switching from NTRIP to Base+Rover help with Fixed stability?
Switching from NTRIP to an independent local Base+Rover setup significantly improves link reliability in remote areas lacking robust cellular coverage. By establishing a dedicated local UHF/LoRa radio link, you eliminate dependence on internet stability and public server routing, ensuring direct correction delivery.
STABLE FIXED SOLUTION. EVEN IN CHALLENGING CONDITIONS.
APEKS 1408-channel receivers track full-constellation satellites for stronger geometry and faster re-acquisition — minimizing Fixed-to-Float cycling in demanding field environments.
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