RTK Fix keeps dropping — how to fix it

When an obstruction passes between your antenna and satellites, signals drop. If enough satellites disappear simultaneously, carrier phase ambiguities can no longer be maintained and Fix drops to Float. This is the most common cause of Fix instability in field conditions.

1. Walk with the antenna as high as possible. A taller pole — 2.0 m instead of 1.5 m — improves line of sight above crops, fences and people.
2. Hold the pole vertical. Even a small tilt blocks part of the opposite sky. Use the bubble level or your receiver's tilt sensor.
3. Reduce the elevation mask to 10°. This admits more low-angle satellites. Do not go below 5°, because very low satellites add more noise than useful geometry.
4. Enable all constellations. GPS, GLONASS, Galileo and BeiDou together give the receiver more alternatives when one part of the sky is blocked.
5. Move the measurement position 2–3 metres. If the point allows it, a small move can clear a local obstruction completely.

Multipath occurs when satellite signals bounce off surfaces before reaching your antenna. The reflected signal arrives slightly later than the direct signal. Your receiver receives both, and the mixture corrupts the carrier phase measurement — causing Fix to degrade or drop.

Multipath is worst near large metal structures such as construction sites, silos and greenhouses, glass buildings, still water and wet horizontal surfaces after rain.

1. Move 5–10 metres away from reflective surfaces. Distance is the most effective multipath fix.
2. Raise the elevation mask to 15° or 20° near buildings. This removes low-angle signals that are most likely to reflect.
3. Use a receiver with multipath mitigation. Trimble Maxwell, NovAtel STROBE and Septentrio AIM+ are designed to reject reflected signals.
4. Avoid measuring immediately after rain. Wet roads, roofs and fields reflect more strongly. Wait 30–60 minutes when possible.
5. Wait for cranes or vehicles to leave the reflection zone. Moving metal objects cause rapidly changing multipath that is particularly difficult to filter.

When the NTRIP correction stream is interrupted — even for a few seconds — your receiver loses the reference data it needs to maintain carrier phase lock. If the gap is long enough, Fix drops to Float and the receiver must re-initialise. This is especially common in areas with variable mobile data coverage.

1. Check signal strength. Watch whether the mobile connection changes from 4G to 3G or Edge at the moment Fix drops.
2. Switch to a dedicated hotspot. A separate hotspot often maintains a more stable connection than phone tethering.
3. Switch carrier. Coverage varies significantly between networks, especially in rural areas.
4. Force 4G only. Prevent the modem from repeatedly switching between network types.
5. Enable auto-reconnect. Make sure the NTRIP client reconnects automatically after a brief interruption.
6. Check bytes per second. A healthy stream is usually a steady 500–2,000 bytes/sec. Drops to zero confirm an internet or NTRIP interruption.

At longer baselines the ionosphere and troposphere introduce differential errors that make carrier phase ambiguity resolution harder to maintain. Fix is more fragile — small signal disturbances that would not matter at a 5 km baseline cause Fix to drop at 40 km.

1. Switch to a VRS mountpoint. A virtual reference station gives an effective baseline of only 1–2 km. This is the most effective fix.
2. Check the physical station distance. If the nearest station is 50 km or more away and VRS is available, switch to VRS.
3. Enable multiple constellations. More satellites give the RTK engine enough redundancy to maintain Fix over a longer baseline.

Even with a good NTRIP connection and short baseline, Fix can drop if the satellite geometry is poor — PDOP above 4–5. Satellite geometry changes continuously throughout the day. A 20-minute window of poor geometry can cause Fix to drop repeatedly even though everything else is fine.

1. Check PDOP in your field software. Look for the satellite quality or PDOP display. If PDOP is above 4, consider waiting for the geometry window to pass — typically 15–30 minutes.
2. Enable all constellations. Adding GLONASS, Galileo and BeiDou distributes satellites across more sky positions, dramatically improving PDOP.
3. Use a satellite prediction app. Apps such as GNSS View or Geo++ RINEX Logger show predicted PDOP values for your location throughout the day. Plan work sessions around the best geometry windows.
4. Lower the elevation mask slightly. Allowing 10° satellites instead of 15° adds more satellites at varied positions, often improving PDOP by 0.5–1.0 in open sky.

Default receiver settings are conservative. In challenging environments — near buildings, under trees or with long baselines — tweaking specific settings can dramatically improve Fix stability.

1. Switch from continuous to fix-and-hold ambiguity mode. Continuous re-initialisation mode drops Fix at the slightest ambiguity uncertainty. Fix-and-hold maintains Fix through brief disturbances. In Emlid Flow: Settings → GNSS → Ambiguity resolution → Fix-and-hold.
2. Enable all satellite constellations. GPS alone gives 8–12 satellites. Adding GLONASS, Galileo and BeiDou gives 30–50 or more. More satellites means more redundancy and a more stable Fix.
3. Reduce the update rate. Running at 10 Hz or 20 Hz in a challenging environment processes more data but also amplifies noise. Dropping to 5 Hz or 1 Hz gives the RTK engine more time per epoch and can improve stability.
4. Check the minimum satellite count. Some field software rejects Fix if fewer than five satellites are tracked. In challenging environments, lowering this threshold to four prevents unnecessary drops when one satellite briefly disappears.