RTK Fix Troubleshooting — Float, Autonomous & No Corrections
Troubleshooting
RTK Fix Troubleshooting — Float, Autonomous & No Corrections
A complete diagnostic guide for when your Trimble GNSS rover won't reach RTK Fixed. Covers radio, internet, and VRS correction methods with step-by-step fixes for every scenario.
In this guide
Overview
Understanding the Three Position States
Before troubleshooting, know what each status actually means — they have very different causes and fixes.
| Status | What it means | Accuracy | Action needed |
|---|---|---|---|
| Autonomous | Rover is not receiving ANY corrections from the base. Working entirely on its own GPS signal. | 0.5–5 m | Fix the correction link — base, radio, or internet |
| Float | Corrections are arriving but the receiver hasn't resolved the integer ambiguity. The solution is not yet locked in. | 0.1–0.5 m | Wait up to 90 sec, or fix signal quality / satellite count |
| RTK Fixed | Full centimeter-level solution. Corrections received and ambiguities resolved. | ±10–15 mm H / ±20 mm V | You're good — start collecting data |
△ Never collect data in Float or AutonomousFloat is NOT accurate enough for construction or survey work. Always wait for RTK Fixed before storing points or staking out.
Autonomous
Stuck on Autonomous — No Corrections at All
Autonomous means the base corrections are not reaching the rover at all. Work through these in order:
1
Verify the base is actually transmitting
- Check the radio/transmit LED on the base receiver — it should blink green approximately once per second.
- In SiteWorks, confirm the base status shows Active and transmitting corrections.
- If the LED is not blinking: reconnect to the base in SiteWorks and restart the base survey. Do not just power cycle — use SiteWorks to restart.
2
Check radio channel and Network ID match
- This is the #1 cause of Autonomous status. Base and rover must be on identical channel and Network ID.
- Reconnect the data collector to the rover in SiteWorks and verify the Network ID matches the base exactly.
- Even one digit off will result in Autonomous — the rover hears nothing.
3
Check radio antenna connections
- Verify the radio antenna is firmly attached to both the base AND rover receivers.
- A loose or missing antenna on the base = no transmission. A loose antenna on the rover = no reception.
- Inspect the antenna connector for bent pins or corrosion — common on used units.
4
Check range and line of sight
- UHF radio (450/900 MHz) requires clear line of sight. Hills, buildings, and dense tree lines block the signal.
- Move the rover to a position with a clear view of the base. If signal appears, you have a range/obstruction problem.
- Typical effective range: 1–3 km with clear line of sight. Range drops sharply with obstructions.
- Raise the base radio antenna height to improve range — higher placement = longer reach.
5
Verify UHF Transmit option is licensed on the base
- The base receiver must have the UHF Transmit option enabled to broadcast corrections.
- Check: connect to the base receiver WebUI → Options — look for UHF Transmit or Radio Transmit in the licensed options list.
- If it is not listed, the receiver can only receive radio corrections, not transmit them. A different base unit is needed or the option must be purchased.
Float
Stuck on Float — Corrections Received but Won't Fix
Float means the radio link is working and corrections are arriving — but the receiver can't resolve the carrier phase ambiguity. This is a signal quality or geometry problem, not a connection problem.
1
Wait — initialization takes time
- After connecting, Float is normal. Give the receiver 60–90 seconds to initialize before troubleshooting.
- In clear sky conditions with good satellite geometry, RTK Fixed should resolve within 30–60 seconds.
- If it has been more than 2 minutes in Float, something is wrong — continue to the next steps.
2
Check satellite count on both base and rover
- Both receivers need a minimum of 5 satellites in common to achieve RTK Fixed. 8+ is recommended for fast initialization.
- Check the satellite count in SiteWorks status bar or the receiver WebUI → Status → Satellites.
- If below 8 satellites: move to an open area with clear sky view. Avoid working under tree canopy, near buildings, or in deep cuts.
- Avoid placing the rover within 400 meters of cell towers, powerful radar, or large metal structures.
3
Check signal strength / multipath
- Multipath (signal reflections off buildings, vehicles, or equipment) causes Float to persist even with good satellite count.
- Move the rover 10–20 meters away from nearby metal objects, vehicles, or walls and check if Fix resolves.
- Avoid operating directly next to heavy equipment or inside metal structures.
4
Check the age of corrections
- Corrections must arrive in near real-time. If the correction age is over 3–5 seconds, the radio link is marginal and the receiver will struggle to fix.
- Check correction age in SiteWorks info bar or receiver WebUI → Status → Position.
- High correction age = radio signal is weak or intermittent. Move rover closer to base or improve antenna placement.
5
Power cycle the rover receiver
- Press and hold the rover power button to power it off completely. Wait 10 seconds. Power back on.
- This resets the carrier phase tracking and often resolves persistent Float when all other settings are correct.
- After reboot, allow 60–90 seconds for satellite re-acquisition before reconnecting in SiteWorks.
💡 Tip — GLONASS interferenceIn some cases, GLONASS satellites can interfere with fast RTK initialization, particularly near other GLONASS-equipped systems. If stuck in Float with good satellite count, try disabling GLONASS tracking in SiteWorks or the receiver WebUI and reconnect. Re-enable after achieving Fixed.
Cycling
Fix → Float Cycling During Work
If the rover keeps dropping from Fixed back to Float during the work session, these are the most common causes:
| Symptom | Likely cause | Fix |
|---|---|---|
| Drops to Float near buildings or equipment | Multipath / signal obstruction | Move away from obstructions. Raise rover pole if possible. |
| Drops to Float in valleys or behind hills | Radio line-of-sight lost | Relocate base to higher ground. Use a repeater radio for extended range. |
| Drops frequently, no pattern | Marginal radio signal — correction age spiking | Check correction age. Move base closer or raise radio antenna height. |
| Drops when walking under trees | Satellite signal interrupted by canopy | Slow down under canopy. Allow re-initialization. Consider xFill if licensed. |
| Drops after base was bumped or moved | Base position changed while transmitting | Stop all work. Reprogram base in SiteWorks. Re-verify on a known point. |
| Drops intermittently on VRS | Cellular connection dropout | Check cell signal. Move data collector to area with stronger signal. Consider a cellular booster or hotspot. |
VRS
VRS / Network-Specific Issues
1
Rover won't fix on VRS — stays in Float
- Verify the NTRIP credentials are correct — wrong mountpoint, username, or password results in Float or Autonomous.
- Try switching to an RTCM3 mountpoint if using CMR. Some VRS networks only output RTCM3 and CMR/CMR+ will not produce a fix.
- Disable SBAS/WAAS tracking in the receiver settings — some VRS networks reject NMEA strings from rovers broadcasting WAAS corrections, causing them to stay in Float indefinitely.
2
Position is 4 feet off on VRS
- This is almost always a units mismatch — US Survey Foot vs International Foot in the state plane coordinate system.
- Check your project coordinate system settings and verify the correct foot definition is selected for your state.
- Also check for a datum mismatch between the VRS network (e.g. NAD83(2011)) and your project (e.g. WGS84).
3
VRS fix is slow — takes many minutes
- Distance from the nearest reference station affects initialization time. Over 35 km from the nearest station = slower fix and reduced accuracy.
- Poor cellular signal = delayed correction delivery = slow initialization. Verify at least 2 bars of LTE signal.
- Try a different mountpoint — AUTO or the geographically closest base station often initializes faster.
Elevation
RTK Fixed But Elevations Are Wrong
If you have RTK Fixed but your measured elevations don't match known benchmarks, the fix is almost never the GPS — it's almost always one of these:
| Cause | Symptom | Fix |
|---|---|---|
| Wrong rover pole height entered | All elevations off by a consistent amount equal to the measurement error | Correct the pole height in SiteWorks. A 10 mm error = 10 mm error on every point. |
| Wrong base antenna height entered | All elevations off by a consistent amount across the whole site | Recheck base antenna height measurement. Re-enter in SiteWorks and restart base. |
| Quick release not accounted for | Elevations off by ~32 mm (QR adapter height) | In SiteWorks antenna height, enter height to bottom of QR only — SiteWorks adds QR offset automatically. Do not measure to the bottom of the receiver. |
| Wrong geoid model or no geoid | Elevations systematically off by a non-round number, varies across site | Verify the correct geoid file is loaded in the project (GEOID18 recommended for US). Re-calibrate with correct geoid. |
| Bad site calibration | Elevations match some control points but not others | Review calibration residuals. Identify and exclude bad control points. Recalibrate. |
Checklist
Full RTK Diagnostic Checklist
- Base transmit LED is blinking green — base is actively broadcasting corrections.
- Base and rover are on the same radio channel and Network ID.
- Radio antenna is firmly connected to both base and rover.
- Both receivers have 8+ satellites tracked.
- Rover has clear line of sight to the sky — away from buildings, vehicles, and tree canopy.
- Rover is within effective radio range of the base (1–3 km clear LOS).
- Correction age is under 3 seconds (check in SiteWorks info bar).
- UHF Transmit option is licensed on the base receiver (check WebUI → Options).
- For VRS: NTRIP credentials, mountpoint, and correction format (RTCM3) are correct.
- SBAS/WAAS is disabled if using a VRS network that rejects WAAS corrections.
- Rover pole height is entered correctly in SiteWorks.
- Base antenna height is entered correctly in SiteWorks.
Still can't get RTK Fixed? 9JA Enterprise can help.
We diagnose and repair Trimble GNSS receivers — hardware faults, option licensing, firmware issues, and more.