Quick Answer
What should I do when my GPS rover won't get an RTK fix?
Check in this order: (1) sky obstructions blocking satellites, (2) correction signal connectivity — radio link or cellular NTRIP connection, (3) base station status if using a local base, (4) controller coordinate system settings, (5) receiver firmware and configuration. Most field no-fix problems are caused by correction signal loss or sky blockage rather than hardware failure.
How to Troubleshoot a GPS Rover That Won't Get a Fix
Applies to: Trimble R10/R12, Topcon HiPer HR, Leica GS18 T, Spectra SP80
A GPS rover stuck in "Float" or "Autonomous" mode is one of the most common field problems on construction sites. The receiver is working — it's receiving satellite signals and computing a position — but it cannot achieve the centimeter-level RTK Fixed solution required for stakeout work. The good news is that the cause is almost always external to the receiver itself: sky blockage, correction signal loss, or configuration mismatch. This troubleshooting guide walks through the checks in order from most likely to least likely cause.
Check 1: Sky Obstruction
RTK initialization requires tracking at least 5-6 satellites simultaneously. Trees, buildings, site equipment, and even heavy cloud cover can reduce satellite count below the minimum. On the controller, navigate to the satellite status screen. On Trimble Access: Instrument > GNSS Status. On Topcon Magnet Field: Survey > Satellite Status. On Leica Captivate: the satellite icon on the main screen. Look at the number of satellites tracked and the PDOP (position dilution of precision).
If satellite count is below 5 or PDOP is above 5, move to a more open location. Even 20-30 feet away can make a significant difference near building corners or tree lines. If you are working in a constrained area that will always have sky blockage, consider a total station for this section — GPS may simply be the wrong tool for the location.
Check 2: Correction Signal Connectivity
RTK requires a continuous correction data stream. For radio-based RTK, check the radio receiver indicator on the controller — most show a correction age (seconds since last correction). Correction age over 10 seconds indicates the radio link is lost or degraded. Move toward the base station, elevate the rover radio antenna, or clear any metal obstructions between rover and base.
For NTRIP (cellular) corrections, check cellular signal strength. Construction sites in valleys, underground, or in building interiors often have poor cellular coverage. Confirm the NTRIP connection status in the controller — on Trimble Access, look for "Connected" status under the correction source. If NTRIP fails, switch to a local radio base if available, or move to a location with cellular coverage. Correction age should stay under 3-5 seconds for stable RTK.
Check 3: Base Station Status
If using a local base station, check that it is still powered on and transmitting. Someone on the crew may have accidentally powered it down, the battery may have died, or the radio antenna cable may have been disconnected. On radio-based systems, the rover controller typically shows "No Corrections" or correction age rising when the base stops transmitting. Walk to the base, confirm it is running and the radio is transmitting (transmit LED active), and check the battery level.
Also confirm the base has not moved. Tripod kicks on a base station produce a position jump that appears as a sudden large residual on a known-point check rather than a no-fix condition, but checking the base setup is worth doing any time results seem off.
Check 4: Controller Configuration
An incorrect coordinate system does not prevent RTK initialization — the receiver gets a fix regardless of what coordinate system is configured. However, a wrong configuration means the position displayed in the correct project coordinate system is wrong. If your check on a known point shows large errors (over 1-2 meters), this is likely a configuration issue rather than a fix problem. Verify the projection, datum, and geoid model in the job settings match the project coordinate system.
On Trimble Access: Jobs > Select Current Job > Coordinate System. On Topcon Magnet Field: Job > Properties > Coordinate System. On Leica Captivate: Jobs > Properties > Coordinate System. Confirm the State Plane zone matches the project location and the datum (NAD83 vs. WGS84) is correct.
Check 5: Receiver and Firmware
Rare but possible: a receiver that was working yesterday may have a firmware issue or internal fault. Cycle the power on both the rover and, if applicable, the base station. A full power cycle clears most transient software states that prevent initialization. If the rover initializes fine in one location but not another, the problem is environmental (sky, corrections) not hardware. If it will not initialize anywhere despite good sky view and confirmed corrections, contact your local Trimble, Topcon, or Leica dealer for diagnostics — modern GNSS receivers have self-test routines that can identify hardware faults.
Frequently Asked Questions
What is the difference between RTK Float and RTK Fixed?
RTK Float means the receiver is receiving corrections but has not yet resolved the integer ambiguity in the carrier phase signal. Position accuracy in Float is typically 0.3-1.0m — usable for rough navigation but not for construction stakeout. RTK Fixed means the ambiguity is resolved and accuracy is centimeter-level (10-30mm). Never stake design points from a Float solution.
Why does my GPS rover lose fix when I walk near buildings?
Buildings block satellite signals (sky obstruction) and cause multipath — reflected signals from building walls confuse the receiver. Both effects reduce effective satellite count and degrade fix quality. The RTK Fixed status drops to Float or Autonomous when the receiver can no longer maintain the integer solution. Move away from the building or use a total station in the affected area.
How long should RTK initialization take?
With good sky view and a strong correction signal, most modern GNSS rovers initialize RTK Fixed in 30-90 seconds. Initialization taking over 5 minutes indicates a problem with sky coverage, correction signal quality, or signal multipath. If it has not initialized in 10 minutes, investigate the cause rather than waiting.
Can I use a GPS rover without a correction signal?
Yes, in autonomous mode — but accuracy is 1-3 meters, far too coarse for construction stakeout. GPS rovers without corrections are useful for navigation, rough location, and marking approximate positions, but should not be used for any layout work requiring accuracy better than 1 meter.
Log GPS rover initialization status, satellite counts, and known-point check results for each field session with Gradelog. Build a troubleshooting history for each instrument in your fleet. Free to start at gradelog.com.
