Why won't RTK change from Float to Fix? Six common causes encountered in the field

By using RTK positioning (real-time kinematic), you can in theory obtain centimeter-level (half-inch-level) high-precision positioning results (Fix solution). However, in actual field work you often hear complaints such as “RTK won’t become Fix and work proceeds with a Float solution” or “corrections aren’t taking effect and we can’t get out of no RTK (single solution)”. When RTK fails to Fix in situations requiring precise positioning, it can cause significant problems such as work delays and reduced trustworthiness of survey data.

There are various possible reasons why RTK cannot obtain a Fix solution, but in many cases the issue can be resolved by reviewing basic checkpoints. In an open sky environment where a sufficient number of satellites can be observed, it is typical for RTK to reach Fix status within several dozen seconds to a few minutes after starting. With high-performance GNSS receivers and algorithms, Fix can sometimes be achieved in about 20 seconds under favorable conditions. If you wait more than 5 minutes and still do not reach Fix, it is likely that some factor is preventing solution convergence (resolution of integer ambiguities).

This article covers six representative causes frequently seen when RTK does not change from Float to Fix, explaining the mechanism of each and the countermeasures to take on site. If you are troubled by “it’s not Fixing…’’ in your daily positioning work, please check whether any of these apply to your case. Correctly identifying and addressing the cause will increase the likelihood of running RTK positioning stably at centimeter-level (half-inch-level) accuracy.

Table of contents

• Cause 1: Poor satellite visibility (insufficient satellite count)

• Cause 2: Multipath interference from reflected signals

• Cause 3: Reference station coordinate input errors or improper installation

• Cause 4: Baseline distance to the reference station is too long

• Cause 5: GNSS setting mismatches (satellites or frequencies)

• Cause 6: Correction data not received / communication trouble

• Summary

Cause 1: Poor satellite visibility (insufficient satellite count)

One of the most fundamental reasons RTK does not become Fix is an insufficient number of available satellites. High-precision RTK positioning requires signals from multiple satellites, and generally it is desirable to be able to use data from at least 5–6 satellites simultaneously. Three-dimensional positioning itself is possible with four satellites, but in such a borderline situation the resolution of integer ambiguities will not be stable and the solution tends to remain “Float.” Even if the satellite count is sufficient, if satellites are clustered in specific directions in the sky the geometric quality worsens (DOP values increase), making it harder to obtain a Fix.

A common background cause of insufficient satellite count or biased satellite geometry is poor visibility around the antenna. For example, if the survey point is in a canyon between buildings or inside or at the edge of a dense forest, much of the sky can be blocked and the number of receivable satellites becomes extremely small. Indoors or in semi-enclosed spaces (such as inside a garage), ceilings or roofs prevent direct reception of satellites, making even basic positioning difficult, let alone RTK Fix. When sky visibility is limited, not only does the number of usable satellites drop, but the satellite geometry tends to become biased. As a result, the observation data may be insufficient and the computation engine can take an extremely long time to converge, or it may never escape the Float solution.

To address this cause, it is most important to ensure the antenna has a clear view of the sky. If possible, move the positioning antenna to an open area and create an environment that allows a wide view of the sky. Even moving a few meters can sometimes allow you to pick up additional satellites. If part of the sky must remain blocked, scheduling the positioning during times when satellite geometry is favorable is also effective. GNSS satellites move with time, so consulting a satellite geometry prediction tool (GNSS planner, etc.) and aiming for times when satellites are well visible can compensate for a shortage of satellites. Also check the receiver settings: if the elevation mask angle is set too high, low-elevation satellites will be excluded and satellite count will decrease, so set an appropriate value around 15 degrees. If possible, using a multi-GNSS receiver that can utilize not only GPS but also GLONASS, Galileo, and Japan’s QZSS (Michibiki) will allow you to capture more satellites and improve the Fix rate.

Cause 2: Multipath interference from reflected signals

“Multipath,” where satellite signals are reflected by buildings, the ground, etc., is a major factor that prevents convergence of the RTK solution. When multipath interference occurs, the receiver receives both the direct signal and signals that traveled via reflected paths, causing errors in the pseudorange and carrier phase observations. When erroneous data like this is mixed in, the RTK computation engine cannot correctly resolve integer ambiguities and cannot maintain the high consistency required for a Fix solution. Multipath errors tend to vary over time and destabilize positioning results, so even if you momentarily achieve a Fix, you may soon revert to Float.

Multipath commonly occurs in environments where there are building facades, large metal structures, fences, vehicles, and other metallic objects nearby. These surfaces reflect GNSS signals like mirrors, and the antenna receives signals with incorrect path lengths. Flat reflective surfaces such as water or asphalt can also have an effect if the antenna installation height is low. Even if sky visibility is good and the satellite count is sufficient, poor data quality due to nearby reflectors can prevent obtaining a Fix. In addition, strong radio interference sources (high-voltage lines, communication antennas, etc.) nearby can introduce noise into GNSS reception and hinder Fix.

To counter multipath, the best approach is to choose an environment that avoids reflections where possible. Keep away from high-rise buildings and metal fences and perform positioning in open areas. If measuring in an environment with many reflectors is unavoidable, mount the antenna on as high a pole or mast as possible to reduce reception of reflected waves from the ground and surroundings. Antennas that can be fitted with a ground plane (a conductive disk) help block signals coming from below. Another useful technique is to achieve Fix once in an open area and then move to the target point; once in Fix, some receivers can maintain the Fix for a short time even if conditions worsen slightly. Also, if there are devices nearby emitting strong radio waves, consider turning them off or moving away from them to reduce electromagnetic noise. Eliminating environmental multipath and interference as much as possible is the quickest path to stable Fix acquisition.

Cause 3: Reference station coordinate input errors or improper installation

RTK applies corrections from a reference station (base) with known accurate coordinates to the rover for positioning. Therefore, if there is a problem on the reference station side, the rover may never obtain a Fix no matter how long it waits. A typical issue is an input error in the reference station coordinates. If the latitude, longitude, or height entered for the base is incorrect, or if a provisional coordinate is set sloppily and the error is too large, the initial RTK calculations can be skewed and integer ambiguity resolution may take a very long time or may never converge. In cases where the base coordinates are offset by tens of meters from the actual position, the inconsistency between the correction information and the measured values can become so large that the computation fails and convergence to a fixed solution becomes practically impossible.

Improper installation of the base antenna is also a factor that prevents Fix. If the base antenna is not securely fixed and physically moves, or is blown over or tilted by strong wind, the reference station’s own observation data becomes unreliable. Naturally, the rover receiving that unstable correction information will also produce unstable solutions, and a Fix that was achieved can revert to Float. Furthermore, if the environment around the base station is poor (narrow sky view, nearby tall structures, etc.), that is problematic: no matter how open the rover’s environment is, if the base station’s data suffers from satellite shortage or multipath, high-quality Fix cannot be expected. In other words, in RTK “reference station accuracy = rover accuracy,” so problems on the base side directly translate into reduced Fix rates.

As countermeasures, if you are installing your own reference station, first recheck the coordinate input and installation method. When setting up a new base, perform more than a short quick survey—preferably average observations for over one hour or place the antenna on a known point to give precise coordinates—so the base coordinates are close to the true value. Also pay attention to the geodetic datum. Mixing Japanese geodetic systems (JGD2011/2022 or global datums) with older local datums can cause meter-level offsets, so ensure the rover and base use the same coordinate system. Regarding height, correct appropriately on the rover side according to the base station height reference (ellipsoid height or geoid height)—for example, convert ellipsoid height to orthometric height using a geoid model if needed. For antenna installation, ensure the base antenna is stably fixed so it cannot move. Secure tripods and poles and place them where workers will not accidentally touch them. If the antenna has been moved during observations, stop positioning and re-measure or reconfigure the reference station coordinates. Also review the environment around the base antenna: select as open a location as possible with minimal surrounding reflection or obstruction. Don’t forget hardware checks such as cable breaks or poor connections and stable power supply.

Even when using public online reference station services or third-party base data, base-side problems can cause Fix failures. If the provider’s base is under maintenance or its observation environment has degraded, there is little you can do. In such cases, try switching to a different base station if possible or reconnecting at a different time. If you combine your own base data with public services, be careful about mismatches in coordinate systems (for example, confusing a local coordinate system with a global one).

Cause 4: Baseline distance to the reference station is too long

If the distance between the rover and the reference station—the baseline length—is too long, RTK may have difficulty achieving Fix. The principle of RTK correction is that “when the base and rover are close, common error sources (satellite clock errors, atmospheric errors, etc.) cancel out.” However, as baseline distance increases, errors experienced at the two locations differ and the portion that can be canceled by correction decreases. In particular, ionospheric and tropospheric delay errors become increasingly different with distance, so residual errors tend to grow over long baselines. As a result, integer ambiguity resolution in RTK becomes unstable and it can take a very long time to converge to a Fix, or in the worst case the solution may remain Float indefinitely.

In general, RTK positioning is more stable and accurate when the baseline to the reference station is shorter. As an operational guideline, a baseline length within roughly 10 km is considered desirable. Up to around 10 km, many of the errors received by the base and rover can be regarded as common, making it relatively easy to achieve accuracy within several centimeters (within several inches). However, as the baseline increases to 20 km or 30 km, residual errors that cannot be removed by correction accumulate and convergence becomes unstable. With good radio conditions and receiver performance you may still reach Fix, but it will generally take longer and be harder to maintain. Beyond about 50 km, obtaining a fixed solution with a conventional single-base RTK setup becomes extremely difficult.

Therefore, when performing RTK far from the reference station, efforts should be made to shorten the baseline. If you operate your own base, consider placing it as close as possible to the survey area. For large coverage areas, consider relocating the base as the work area moves. If using existing reference station services, choose data from the nearest base or virtual reference stations (VRS) when possible. When long distances must be covered, using a multi-frequency GNSS receiver is important: dual-frequency (L1/L2) or better receivers handle ionospheric errors more effectively than single-frequency (L1-only) receivers and increase the chance of Fixing over long baselines. Also, during times of high solar activity (daytime) when the ionosphere is disturbed, long-distance RTK is particularly difficult—if you must perform tens-of-kilometers-scale positioning, consider conducting it at night or early morning when the ionosphere is relatively stable. If it remains difficult, instead of forcing real-time Fix, consider alternatives such as leveraging a network of reference points or using PPP (precise point positioning) with post-processing to achieve high precision.

Cause 5: GNSS setting mismatches (satellites or frequencies)

RTK will not Fix if the GNSS settings used by the base and rover do not match. RTK requires both ends to use common satellite observation data for computation. Therefore, if one side uses certain satellites or different frequency settings, common observations are not obtained and corrections cannot be applied correctly. For example, if the base tracks both GPS and GLONASS but the rover is set to use GPS only, GLONASS-originated corrections will be ignored, reducing the effective satellite count and making the solution less stable. Conversely, even if the rover supports multi-GNSS, if the base data is composed of GPS only, the RTK will effectively be GPS-only and may remain Float depending on the environment.

Also pay attention to frequency band mismatches. If the base outputs L1/L2 dual-frequency data but the rover is a single-frequency receiver (L1 only), L2 corrections cannot be utilized as-is. Dual-frequency RTK combines observations from both frequencies for error correction; if one side is single-frequency, common computation conditions are not met and Fixing becomes difficult. When linking single-frequency receivers, set the base to output L1-only correction mode as well (or ideally upgrade both to multi-frequency receivers).

Furthermore, check correction data format compatibility. RTK differential corrections typically use RTCM messages, but depending on base station software or NTRIP service settings, the rover may receive message types it cannot interpret. Using older receivers, there can be cases where newly added messages (e.g., messages for Galileo or corrections needed for GLONASS integerization) are unsupported and parts of the data cannot be read, resulting in no Fix. Special augmentation signals like Japan’s QZSS (Michibiki) may require dedicated compatible equipment or settings. Thus, protocol incompatibility between the chosen base and rover combination can be a cause of non-Fix.

As a countermeasure, standardize base and rover settings when installing an RTK system. First, enable all satellite systems supported by both receivers so they can always track common satellites—check whether one side has GLONASS or Galileo turned off. Using multi-GNSS as much as possible increases shared observation data and improves Fix rate. Likewise, align the frequency combinations used by base and rover: if one side is L1-only, set the other to L1-only, or preferably use multi-frequency receivers on both ends. Also adjust the correction output format to match the rover’s device specifications. For NTRIP connections, some services allow you to select the message types provided. Confirm that the minimum necessary messages (e.g., base coordinates and GPS/GLONASS observation data) are included, and exclude unnecessary messages to maintain compatibility. Consider firmware updates for older receivers to support new formats. If problems persist after changing settings, rebooting the equipment can help: occasionally software glitches prevent changes from taking effect. Ensuring GNSS settings on both base and rover are correctly synchronized will solve many Fix-failure issues.

Cause 6: Correction data not received / communication trouble

RTK requires continuous reception of correction data from the reference station to obtain a Fix solution. Therefore, if correction information is not reaching the rover, RTK will never Fix. In other words, “without correction data RTK is the same as standalone positioning,” and you will remain in a Float solution (or no RTK) regardless of time. Typical causes are communication troubles. In network RTK, problems often occur with the internet connection used for NTRIP. In mountainous or suburban areas where mobile network signal is weak, or where smartphone tethering has been turned off and data communication stopped, corrections will not arrive and the solution can revert to Single. Misconfiguration of NTRIP settings (incorrect host name, port number, mountpoint name, user ID or password) is also a frequent reason the connection is not established.

In systems using short-range radio or digital radio to broadcast base corrections, corrections will be interrupted if you move out of the radio range or if obstacles block the signal. Channel interference or antenna faults can cause partial data loss. Even when a connection exists, if the correction data stream has many errors (packet loss or CRC errors), the receiver cannot reconstruct the information and computations halt. Also, if the base’s retransmission interval is extremely long (for example, data is sent only once every 30 seconds), the latest corrections may not be timely and the solution can revert to Float. In any case, RTK’s benefits cannot be realized without stable reception of correction data, and achieving a Fix is difficult under such conditions.

To address communication and reception troubles, first check the reception status of correction data. RTK-capable GNSS receivers and apps display correction reception status and parameters such as “differential age.” If these indicators are not updating or show errors, communication failure is suspected. When using NTRIP, verify that the rover’s terminal (smartphone or router) is properly connected to the internet. If signal conditions are poor, move to a spot with better reception, toggle airplane mode on and off to re-establish the connection, or try other basic measures. If that does not help, switching to another SIM card or provider may work. Also recheck NTRIP settings for even a single-character typo. For radio systems, ensure transmit/receive antennas are correctly connected and placed with a good line of sight, and change channels if interference is present. Additionally, verify that the correction data source itself is healthy: the provider’s service could be under maintenance or experiencing degraded accuracy. In such cases wait and reconnect later or switch to another available service. The key is to ensure a stable, continuous reception environment for correction data, which strongly influences RTK Fix success rates.

Summary

Above, we explained six causes to consider when RTK remains at a Float solution and does not Fix. When you are stuck in the field without Fix, it is essential to return to basics and check one by one—from satellite reception conditions to reference station settings and communication status. In many cases, reviewing the points raised here will resolve the problem and allow you to obtain Fix reliably.

That said, checking and addressing all these factors each time is time-consuming. One solution gaining attention is the use of new GNSS devices that enable high-precision positioning easily. One such device is LRTK (an iPhone-mounted GNSS high-precision positioning device). By attaching LRTK to an iPhone and using its dedicated app, anyone can easily perform centimeter-level (half-inch-level) positioning. Reception of corrections from a reference station and various settings are managed seamlessly in the app, so users can obtain stable Fix solutions without deep technical knowledge. These devices greatly reduce the burden of ensuring satellite environment and equipment settings that have been challenging in conventional RTK operations, making surveying tasks on site smarter. If you are struggling with RTK Fix issues, consider introducing such latest devices into your workflow.