Quick Answer
The Emlid Reach M2 is a compact multi-band RTK GNSS receiver designed for UAVs. It tracks L1/L2/L5 signals from GPS, GLONASS, Galileo, and BeiDou, delivering centimetre-level positioning for photogrammetry and survey-grade drone mapping.
What the M2 Is
The Reach M2 measures just 46 × 46 mm and weighs under 30 g — small enough to sit on almost any airframe. It runs Emlid's own firmware and is configured through the free Emlid Flow app (iOS and Android). The module supports two correction modes: real-time RTK via a LoRa radio link, and post-processed kinematic (PPK) where corrections are applied after the flight.
For mapping work, the difference between standard GPS (2–5 m accuracy) and RTK/PPK (1–2 cm) is the difference between a usable orthomosiac and a costly re-flight. If you are producing survey deliverables, centimetre positioning is not optional.
Physical Installation on Your Drone
Antenna Placement
Mount the multi-band GNSS antenna on the top of your airframe with a clear view of the sky. Keep it at least 10 cm away from video transmitters, ESCs, and other sources of RF noise. A carbon-fibre top plate with the antenna raised on a small mast works well. The antenna ground plane improves multipath rejection, so avoid flush-mounting it directly against a conductive surface.
Wiring to Pixhawk or ArduPilot
Connect the M2's UART TX/RX to a spare serial port on your flight controller — typically SERIAL4 on a Pixhawk 4 or TELEM 2 on a Cube. Set the corresponding SERIALx_PROTOCOL parameter to 20 (RTK/GPS base) in ArduPilot. The M2 draws power from the FC's 5 V rail. Double-check the pinout against the Emlid documentation before plugging anything in — the JST-GH pin order differs between Emlid and Holybro connectors.
For a full walkthrough of the flight-controller side of the setup, see our ArduPilot RTK integration guide.
RTK Mode Setup
In RTK mode, the M2 on your drone (rover) receives real-time correction data from a second receiver on the ground (base). The Reach M2/M+ LoRa radio provides the wireless link between them.
- Set up the base receiver over a known point (or average its position for 5–10 minutes).
- In Emlid Flow, configure the base to output RTCM3 corrections at 1 Hz.
- Pair the LoRa radios to the same frequency and air data rate.
- On the rover M2, set the correction input to LoRa and the positioning mode to "Kinematic".
When the link is established, Emlid Flow will show "Fix" — you now have centimetre accuracy in real time. This is ideal when you need to verify coverage or trigger the camera at precise positions during the flight.
PPK Mode Setup
PPK skips the radio link entirely. Both the base and rover log raw observation data during the flight. After landing, you download the files and process them in Emlid Studio (free desktop software).
- Configure both receivers to log raw data at 1 Hz or higher.
- Fly your mission as normal.
- Download the .ubx or .rinex files from both receivers.
- Process in Emlid Studio to generate corrected position data.
- Geotag your images using the corrected position log.
PPK is simpler in the field (no radio link to maintain) and often more reliable because it is not affected by radio interference or signal dropouts. For a deeper comparison of the two methods, see our RTK vs PPK for drone mapping article.
Emlid Flow Configuration for Mapping
Open Emlid Flow and connect to the M2 via Bluetooth or Wi-Fi. Key settings for mapping flights:
- Positioning mode: Kinematic (RTK) or Static + Kinematic (PPK)
- Correction input: LoRa (RTK) or disabled (PPK)
- Logging: Raw data at 1 Hz minimum (PPK) or RINEX for third-party processing
- Update rate: 5 Hz for fast-moving drones; 1 Hz is fine for slow survey flights
- Elevation mask: 15° to reduce multipath errors from low-angle satellites
The Reach M2 kit with helical antenna includes everything you need — the M2 module, the multi-band antenna, cables, and a helical antenna option for ground-base use where a flat ground plane is impractical.
Tips for Better Results
- Always use a multi-band antenna. L1-only antennas cannot resolve integer ambiguities reliably. The multi-band antenna is essential for centimetre accuracy.
- Log raw data even in RTK mode. If the radio link drops mid-flight, you can fall back to PPK processing with the logged data.
- Wait for "Fix" before take-off. A "Float" solution means the ambiguity is not fully resolved — accuracy will be decimetre, not centimetre.
- Check satellite geometry. Use Emlid Flow's sky plot before flying. PDOP below 3 and at least 12 satellites in view is a good baseline.
- Keep the antenna level. Antenna tilt degrades positioning. For aggressive banking flights, consider an antenna with a wider reception pattern or reduce bank angles over the survey area.