Unicore Communications UM982

The UM982 from Unicore Communications of China is a multi-frequency RTK and heading module with two antennas in an LGA package of 16 x 21 x 2.6 mm, based on Unicore's NebulasIV SoC. It is not assigned to a drone class but is a building block that manufacturers fit into flight modules, for example Holybro in the H-RTK Unicore UM982.

The chip has 1,408 channels and handles GPS, GLONASS, Galileo, BeiDou, QZSS and SBAS. The main antenna uses among others GPS L1C/A, L2C, L2P(Y) and L5, BeiDou B1I, B3I, B1C, B2a and B2b, GLONASS G1 and G2, Galileo E1, E5a, E5b and E6, and QZSS up to L6; the second antenna receives an L1/L2 set. B2b depends on the firmware. For RTK Unicore states 0.8 cm + 1 ppm horizontally as RMS, a spread measure covering roughly two thirds of the measurements that cannot be compared directly with the CEP figures of other modules. The heading is 0.1 degrees at a 1 m baseline. The rate is 20 Hz. Connection is through three UARTs; SPI, I2C and CAN are available only with special firmware. NMEA 0183, the Unicore format and RTCM 3.x are spoken. The chip weighs 1.82 g.

The baseline is the distance between the two antennas: the longer it is, the better the heading, because the same position error then gives a smaller angle. Heading from two antennas is independent of the magnetic field and is available even at standstill. A chip is not an aircraft: the duties of the EU drone regulation arise at the aircraft, where geo-awareness and remote identification (from class C1) rest on the GNSS position. Correction data come from your own base, a radio link or NTRIP.

For selection, the room on the frame for two antennas with a clear view and the widest practical spacing decides. The spacing is measured and entered in the flight controller; a wrong value distorts the heading. Upkeep includes the firmware and checking the antenna leads.