Specifications

• Ublox ZED-F9P GPS Receiver

  • Ultracap backup power for fast (hot-start) restarts

  • EMI shield over receiver for improved EMI immunity

• IST8310 Magnetometer

• Safety-switch and safety LED

• RGB LEDs for status indication

  • NCP5623CMUTBG I2C Driver

• BMP388 Baro on I2C bus

• External, active antenna (Maxtena M7HCT)

  • SMA connector

• STM32 MCU for future CAN-based communication

  • FW updates through USB connector

• Connectivity:

  • USB-C

    • 2-way USB Switch to MCU and F9P

  • SMA for active antenna (20mA max)

  • 4-pin CAN Bus (dronecode compliant)

  • 8-pin UART/I2C

• Power:

  • Input from either (diode OR'd):

    • USB (5V)

    • CAN (4.7 to 25.2V)

    • UART (4.7 to 25.2V)

  • Power Consumption <1W

RTK Performance over range

The performance of RTK over long distances is typically limited by:

• Telemetry link: You must have a telemetry link between the aircraft and ground station,

• RTK degradation over distance: As the aircraft moves away from the base station, the RTK accuracy will degrade. The F9P RTK GPS receiver spec is 0.01m CEP (Circular Error Probability) + 1ppm for both vertical and horizontal.

  • For example, at 10km distance from base station, the typical accuracy would be 0.01m + (1km * 1/1,000,000) = 0.02m CEP

GPS Origin Point

GPS coordinates reported from this base station are centered around a point 35mm from the base of the antenna.

Mechanical Dimensions

Prerequisites

For use on Alta, the following is necessary:

• Alta X

• Two RTK Modules (Rover and Base Station)

• Alta SW 1.3 or above

• Datalink (FRX Pro recommended)

• Computer (Mac or Windows) running Alta QGC 1.3 or above

• Sturdy mount for base stations GPS. Tripod with 1/4-20 mount is recommended

• USB C cable

I2C Address Table

Description	PN	I2C Address (7-bit)
RGB LED Driver	NCP5623C	011 1001 ($39)
Barometer	BMP388	111 0111 ($77)
Magnetometer	IST8310	000 1110 ($0E)

Connector Pinout

CAN Ports - GH-4 Pin

Peripheral CANbus for future expansion.

Pin	Signal	Voltage (V)
1	VCC	+5V to 25.2V
2	CAN_H	+5V
3	CAN_L	+5V
4	GND	GND

UART/I2C Ports - GH-8 Pin

Peripheral CANbus for future expansion.

Pin	Signal	Signal Notes
1	VCC	+5V to 25.2V
2	SERIAL: FC to GPS	3.3V TTL
3	SERIAL: GPS to FC	3.3V TTL
4	I2C-SCL
5	I2C-SDA
6	SAFETY SWITCH	3.3V = PRESSED 0V = NOT PRESSED 4.7k pull-down
7	SAFETY LED	3.3V, pull low to turn on LED. 20mA sink
8	GND	GND

GPS Antenna Compatibility

The following antennas have been tested with the Freefly RTK GPS module:

• Maxtena M7HCT

• UBlox ANN-MB multi-band antenna

The Freefly RTK modules are shipped with Maxtena M7HCT multiband antennas. However, the GPS is compatible with other SMA, L1/L2 multiband antennas.

Sensor Rotation

The IST8310 defines its coordinate system using left-hand rule, which is corrected in PX4 to be right-hand. Orientation is shown below in both native and PX4-corrected coordinates.

Alta X Orientation

When installed on Alta X, the PX4 orientation is with respect to the front-left vertical mounting surface. In other words, when installed on the front-left (where the standard GPS is installed), the "external mag" orientation should be set to Yaw 0° (ie, No rotation). When installed on the diagonal side (rear-right), the orientation should be set to Yaw 180°.