Checklist when RTK Won’t Fix: 5 Points to Check

RTK positioning (real-time kinematic) can provide centimeter-level high-precision position information (Fix solution) (cm level accuracy (half-inch accuracy)) when conditions are right. However, in the field you may often face the problem that “RTK won’t fix.” There are various causes for not obtaining a Fix solution, but in many cases the issue can be resolved by reviewing basic points. This article explains five checkpoints to confirm when RTK won’t fix. Please use this as practical knowledge to help stabilize positioning.

Table of Contents

• Check satellite reception

• Check the positioning environment (obstructions and multipath)

• Check correction data reception and communication status

• Check base station settings and baseline length

• Check GNSS receiver settings and hardware

• Simple surveying with LRTK

• FAQ

Check satellite reception

The first thing to check is the number and geometry of satellites available. For RTK positioning, it is important to be able to stably receive signals from at least 5 satellites. If the satellite count is low or satellites are clustered in a particular direction, the information needed for position calculation may be insufficient and a Fix solution will be difficult to obtain. In general, three-dimensional positioning is possible with 4 satellites, but 5–6 or more satellites simultaneously available are desirable to obtain a Fix solution. Check the GNSS satellite count and DOP values (dilution of precision) on your positioning software or receiver status screen to ensure the required satellite count is met.

The balance of satellite distribution is also important. If satellites are biased to one area of the sky, the DOP will be high (accuracy poor) and the Fix will be unstable. The more evenly satellites are distributed across the sky, the lower the DOP and the better the accuracy. If satellite geometry is poor at the time, consider checking satellite visibility predictions with a GNSS planner and performing surveying at times with better geometry. Also verify that the elevation mask in the receiver settings (which excludes low-elevation satellites) is not set too high. Setting the elevation mask to around 15° allows use of low-elevation satellites to a reasonable extent, balancing satellite count and accuracy. In particular, using a multi-GNSS receiver that supports multiple constellations (GPS, GLONASS, Galileo, QZSS, etc.) increases the number of usable satellites and improves the Fix rate.

Check the positioning environment (obstructions and multipath)

The surrounding environment at the site is another major cause of RTK not fixing. GNSS signals can be blocked by building facades or tree branches, or they can be reflected (multipath). In locations where the antenna’s sky view is narrow, you may not secure enough satellites to obtain a Fix solution. Nearby tall buildings, metal fences, or large vehicles can reflect incorrect signals, causing errors in the position calculation.

As a countermeasure, the basic rule is to perform positioning in a location that is as open as possible. If you can move to a place with an unobstructed sky, even moving a few meters may increase the number of received satellites and lead to a Fix. If you must survey near buildings or structures, try mounting the antenna as high as possible or shifting the measurement point slightly. Another effective method is to obtain a Fix at an open location during initial setup and then move to the target point. Some receivers can maintain a Fix for a short time even if conditions worsen after an initial Fix.

Countermeasures for multipath are also important. If you can attach a ground plane (conductive plate) to the antenna, do so to block reflections from the ground or below. High-performance antennas and receivers may include multipath suppression features, but the basic principle is to create an environment that avoids reflections. Also check for strong radio interference sources (high-voltage lines, communication antennas, etc.) nearby. Strong electromagnetic noise can add noise to GNSS signal reception and prevent Fix. Reviewing the site’s radio environment as well as physical obstructions is a shortcut to obtaining a Fix solution.

Check correction data reception and communication status

For RTK positioning, you will never get a Fix unless correction data from a base station is being received. Therefore, confirm that correction data is being received properly. If you are using network RTK, first check the NTRIP connection status. Use the dedicated app or receiver screen to verify that “Correction data: receiving” is displayed and that the communication icon is normal (e.g., green). If the status shows not connected, recheck the NTRIP settings (server URL, port, mountpoint name, user ID/password). Even a single incorrect character will prevent server connection. If you use a cellular connection, verify that your smartphone or mobile router is connected to the Internet and that signal strength is sufficient.

Even if you are receiving correction data, pay attention to the type of correction information being received. For example, ensure both the base and rover are using the same satellite systems. If one is using GLONASS while the other has GLONASS turned off, the satellite data will not match and a Fix solution cannot be established. Always match settings on both units. Also check the correction data format and frequency band. Single-frequency receivers require single-frequency corrections (e.g., MSM4 format), while multi-frequency receivers require multi-frequency corrections (e.g., MSM7 format) for high accuracy. Receiving an unsupported format will prevent proper interpretation and can prevent a Fix.

Monitor the communication status continuously. If the correction data has a time lag or frequent packet loss, the solution may drop to Float or become unstable. If your receiver displays items such as “Age of Differential” or received RTCM message count, you can check whether corrections are arriving without delay. If delays are large, improve the communication environment or disconnect and reconnect. It can also help to try another NTRIP service or another communication method (e.g., change the SIM carrier, switch to a Wi‑Fi router). For local radio RTK, check the radio range and channel interference. If there are obstacles between the base and rover, the radio signal may not reach and corrections will be interrupted, so ensure line of sight and appropriate antenna height.

If you are using a virtual reference station (VRS) service, verify that the rover’s approximate position is being sent correctly. If you registered your location incorrectly during initial setup or position transmission is OFF, appropriate correction data will not be provided and the rover will not Fix. Recheck the “position transmission” item in the connection settings.

Check base station settings and baseline length

Next, check for problems caused by base station (reference station) settings and position. If you operate your own base station, confirm that the base station coordinates are set accurately. Ideally, assign coordinates with as little error as possible. If you operate with provisional coordinates that are far from the actual location, the initial values in solution calculation may be off and the Fix may be unstable. Errors of tens of meters or more can cause integer initialization to take longer or fail. If operating in the same public coordinate system, ensure the base station’s geodetic datum (JGD2011, WGS84, etc.) matches the rover’s. Different coordinate systems between base and rover can cause offsets after applying corrections and prevent proper Fix.

Check the baseline length (distance between base and rover). RTK precision and time to Fix tend to worsen as the baseline increases. Generally, a baseline within about 10 km is favorable for obtaining a Fix, but as distance increases to 20 km or 30 km, differential ionospheric and tropospheric errors increase and Fix may take longer or be unstable. At distances beyond 50 km, some environments may rarely achieve a Fix. As countermeasures, place the base station closer to the work area where possible, or use public continuously operating reference stations or VRS services to effectively shorten the baseline. Network RTK services generate virtual base stations near the user, making it easier to maintain accuracy at longer ranges. Conversely, if a local RTK base station is too far away, it may be the cause of no Fix; consider using a network service or adding more base stations.

Also, the base station’s installation environment affects quality. If the base antenna is surrounded by tall buildings or placed in a multipath-prone area, those errors propagate to the rover. Install base stations in locations with good sky view, in safe positions, and measure antenna height precisely. Also verify that the base station is functioning correctly (transmission not stopped, power and connections normal).

Check GNSS receiver settings and hardware

Finally, check the settings and hardware of the GNSS receiver and peripheral equipment you are using. Surprisingly, equipment connection faults or configuration mistakes can cause failure to Fix. For example, if you use an external antenna, inspect for loose or broken cables. If the antenna connector is not firmly attached, satellite signals will be weak and positioning accuracy will suffer. If a device that used to Fix suddenly stops Fixing, consider antenna cable issues or receiver hardware failure. If your RTK device is used in conjunction with a smartphone or tablet, app glitches or freezes may be the cause; in that case, restart the app or reboot the phone/tablet and reconnect.

Also review internal receiver settings. Confirm that positioning mode and satellite settings have not changed unknowingly. For example, if the rover is left in “Static” mode while moving, the solution will not be stable; conversely, using “Kinematic” mode while measuring a stationary point for a long time can introduce unnecessary errors. Pay attention to ON/OFF settings for satellite systems (GPS, GLONASS, etc.). As mentioned earlier, base and rover must use the same satellite systems; if GLONASS is disabled on one, disable it on both or enable it on both. Some positioning software allows reloading base station information, which can sometimes lead to a Fix, so try reloading when appropriate.

On the hardware side, do not overlook antenna installation techniques appropriate to the environment. Mount the antenna as level as possible and avoid tilt. Tilt introduces bias in the satellite reception pattern and degrades accuracy. Use a level when using poles or tripods. Raising the antenna higher reduces the impact of nearby obstructions, but ensure it is secured against wind-induced movement. Also, restarting equipment can be effective; power off and then restart both base and rover, bringing the base online before starting the rover can lead to improvement.

If RTK still won't Fix, consider equipment limitations or external factors. Single-frequency receivers in particular may take longer to Fix or be unstable due to ionospheric errors. If possible, using multi-frequency-capable equipment can significantly improve performance. Solar activity and atmospheric conditions can also temporarily degrade accuracy; in such cases, wait and try again later.

Also check for GNSS receiver and app firmware/software updates. Older versions may contain bugs affecting RTK solutions, and updates can improve Fix rates. Apply the latest firmware provided by the manufacturer to maintain stable Fix acquisition.

Simple surveying with LRTK

Above are the points to review when RTK won’t Fix. Even after checking these, some users may find equipment handling difficult or may want an easier surveying workflow. For such users, we recommend simple surveying with LRTK. The LRTK series are compact high-precision GNSS receivers provided by Reflexia Corporation, designed so anyone on site can easily utilize centimeter-precision positioning (cm level accuracy (half-inch accuracy)).

Although pocket-sized, LRTK receivers support multi-GNSS and multi-frequency, and realize high-precision RTK positioning in conjunction with a dedicated app. Operation is simple: connect to a smartphone or tablet and operate the app. The app guides you through complex settings, so specialized knowledge is not required. For example, the smartphone-integrated model LRTK Phone is an ultra-compact receiver that attaches to an iPhone and weighs only 125 g. It can be carried on site at all times, allowing instant positioning and recording when needed. Some models include tilt compensation, which automatically corrects the reported tip position when the antenna is tilted.

LRTK also supports Japan’s QZSS CLAS correction signals, enabling receipt of corrections via satellite and obtaining a Fix even in mountainous areas without Internet coverage. Measured data can be synchronized to the cloud in real time, allowing coordinates and notes taken in the field to be shared immediately. Introducing simple surveying with LRTK enables on-site staff to perform tasks previously dependent on surveying specialists, lowering the barrier to RTK and directly improving on-site productivity.

FAQ

Q1: How many satellites are required at minimum to obtain an RTK Fix solution? A: Theoretically, 4 satellites are sufficient for three-dimensional positioning, but to stably obtain an RTK Fix it is said that 5–6 or more satellites are needed. The more satellites available the better; using a receiver that supports constellations beyond GPS—such as GLONASS, Galileo, and QZSS—will increase the satellite count and improve Fix rate.

Q2: If RTK is slow to Fix, how long should I wait? A: Under good conditions, a Fix usually occurs within tens of seconds to a few minutes after powering on the receiver or starting positioning. If it has been more than 5 minutes without a Fix, there is likely some issue. In that case, recheck the points discussed in this article (satellite count, environment, correction data reception, etc.). Continuing to measure while staying in a long Float solution will not improve accuracy, so identify the cause and take countermeasures.

Q3: Can weather or time of day make Fixing more difficult? A: Ordinary rain or cloud cover does not greatly attenuate GNSS signals, but ionospheric disturbances or satellite geometry can cause time-of-day effects. For example, the 14:00–17:00 period is said to be more susceptible to ionospheric effects that reduce accuracy. In urban areas, satellites may be at low elevations and enter building shadows at certain times. If environmental factors make Fix difficult, try changing the time and retry.

Q4: Is it acceptable to use a Float solution for positioning? A: Float solutions are less accurate than Fix and typically have errors on the order of several tens of centimeters to about 1 m. For precise surveying or construction control, a Float solution is insufficient. If a Fix is not obtained quickly, do not hastily record Float values; wait for a Fix or attempt positioning again later. If a Fix is impossible, switch to static positioning (long observation with post-processing) or improve accuracy by taking multiple quick observations and averaging.

Q5: What can I do if the base station is far away? A: Long distances from the base station make Fixing difficult, so using a public network RTK (VRS) service is effective when possible. VRS generates a virtual base near the user and solves distance issues. For cases that must cover long distances, installing relay stations or using higher-power radios may be necessary to strengthen communication. If still difficult, consider temporarily relocating a base station nearer the survey points or performing post-processing (PPK).