Why am I stuck on Float and not reaching Fix?

This is the single most common cause of persistent Float on DJI drones. DJI's RTK processing engine requires Doppler observations to resolve integer ambiguities. Doppler is included in MSM5 and MSM7 but not in MSM4. When a DJI drone connects to an MSM4 mountpoint, corrections flow normally and the connection appears successful — but Fix never arrives because the Doppler data needed for DJI's initialisation is absent.

The symptom is unmistakable: NTRIP connected, bytes flowing, stable Float for many minutes, never converging to Fix regardless of sky conditions.

1. In DJI Pilot, go to RTK Settings → Custom Network RTK. Change the mountpoint from RTCM3_NL to RTCM3_NL_MSM5.
2. Disconnect and reconnect. DJI should reach Fix within 60 seconds in open sky.
3. For long-baseline DJI flights, use RTCM3_NL_VRS instead. The short effective baseline improves Fix stability.

There are two subtle ways corrections can appear to flow but not actually help the receiver: the stream contains no corrections for the satellites your receiver tracks, or the connection drops and reconnects repeatedly. Every dropout resets the ambiguity-resolution timer to zero.

1. Verify bytes per second is non-zero and stable. The counter should show a steady 500–2,000 bytes/sec. If it repeatedly falls to zero, fix the internet connection first.
2. Check the RTCM message types. You need at minimum MSM4 messages such as 1074, 1084, 1094 and 1124, or equivalent. Legacy-only 1004/1012 data may not match the receiver.
3. Check VRS GGA transmission. If you use a VRS mountpoint without GGA enabled, the server may stream nothing. Enable GGA and reconnect.
4. Try a dedicated hotspot. Phone tethering can be less stable. A dedicated hotspot often resolves Float caused by repeated stream interruptions.

Ambiguity resolution requires sustained, clean carrier-phase measurements from multiple satellites simultaneously. Trees, buildings, vehicles and terrain can block or reflect signals and interrupt the continuous tracking required for Fix. Even partial canopy can scatter L1/L2 signals enough to keep a receiver in Float.

1. Move to the most open spot available. Even five metres can make a significant difference. The antenna needs a clean hemisphere of sky above 10–15°.
2. Stand still. Movement during initialisation compounds the problem. Stop walking or driving and wait at least 60 seconds.
3. Lower the elevation mask to 10°. Where supported, a lower mask allows useful low-angle satellites to improve geometry.
4. Move away from metal structures. Metal roofs, silos, greenhouse frames and vehicles create strong multipath. Keep at least ten metres away.

At long baselines, ionospheric and tropospheric errors at the reference station and rover diverge. Corrections from the distant station no longer describe the atmosphere at your location accurately enough for the receiver to resolve integer ambiguities with confidence.

1. Switch to the VRS mountpoint. VRS generates a virtual reference station around 1–2 km from you. Enable GGA and connect to RTCM3_NL_VRS.
2. Check the sourcetable distance. If the nearest physical station is more than 25 km away, VRS is normally the better choice.
3. Use a dual-frequency receiver. Single-frequency receivers are usually limited to baselines of around 10 km before ionospheric errors prevent Fix.

The ionosphere delays satellite signals by an amount that varies with solar activity. During geomagnetic storms and solar maximum periods, these delays can change rapidly. This can stop ambiguity resolution even with short baselines and good sky conditions.

1. Work early morning or evening. Ionospheric activity is typically lowest during the first two hours after sunrise and later in the evening.
2. Switch to VRS. Network-wide ionospheric modelling partially compensates for elevated ionospheric noise.
3. Check space weather. A Kp index above 5 often causes RTK problems. Postponing work until the storm passes may be the only reliable option.
4. Use a triple-frequency receiver. L5 signals are more robust to ionospheric noise than L1/L2 and can maintain Fix in more difficult conditions.

Default receiver settings are designed to be safe across a wide range of conditions. In challenging environments, those defaults can be too conservative and prevent Fix even when it would be achievable with a small adjustment.

1. Switch ambiguity resolution to Fix-and-hold. In Emlid or RTKLIB, this maintains a resolved integer solution through brief disturbances instead of re-initialising continuously.
2. Enable all constellations. GPS, GLONASS, Galileo and BeiDou together provide much more redundancy than GPS alone.
3. Reduce update rate to 1–5 Hz. In a weak environment, reducing the rate gives the RTK engine more averaging time per epoch.
4. Set the minimum elevation mask to 10°. Higher masks can exclude useful satellites and weaken satellite geometry.