GNSS / GPS Modules

Overview

The GNSS module interprets the raw satellite signals collected by your antenna, turning them into usable location data.

The systems work with NMEA strings (data that came from GNSS receivers with actual position, ground speed, heading, and so on.) So, to know where your tractor is you need one.

GNSS/GPS naming confusion

GNSS stands for Global Navigation Satellite System. It’s the Collective name for multi GNSS Satellites like GPS, Glonass, Galileo, Beidou and QZSS. Mostly everyone calls their system a GPS Autosteer System, but GPS is the American Satellite system. That’s where the confusion often comes from.

Module selection

In the world are AgOpenGPS there are basically two GNSS modules of interest:

  • Ardsusimple SimpleRTK2B (available in standard or micro sizes)
  • Unicore UM982

Ardusimple’s SimpleRTK2B F9P receiver boards are the most popular at present (2025). They are very good and low priced (if you are in certain parts of the world) multi GNSS receivers and also RTK ready. For a good auto steer system you need very high accuracy - with RTK corrections fed into the SimpleRTK2b board it can achieve <2cm precision.

If you want to connect to an RTK signal in your setup, you can find more information on the RTK hardware section of the Hardware quickstart guide

Single or Dual

AgOpenGPS is configurable with one or two GNSS modules (and one or two antennas respectively). Some users report high performance at low speeds with dual systems, but generally performance of a single antenna + IMU system is very good. For beginners it is likely best to start with single + IMU, test it, and see if dual is required.

If you are going for a dual setup, antennas must be placed at least 150cm apart. image

Ardsusimple SimpleRTK2B

Standard or Micro

Here, you’ll be following your board choice - you can’t fit Micro GPS modules to a standard board, or vice versa.

Standard: https://www.ardusimple.com/product/simplertk2b/

Standard with Antenna https://www.ardusimple.com/product/simplertk2b-basic-starter-kit-ip65/

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or Micro: https://www.ardusimple.com/product/simplertk2b-micro/

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Options :
Variant - ZED-F9P (absolutely NOT F9R!!)
RF connector - SMA
Form Factor- Through hole

If you want to use it standalone or with an rtkbase, here’s a breakout board - then USB should recognize it: https://github.com/AgOpenGPS-Official/Boards/tree/main/Ublox%20F9P/BuckWheat%20Micro%20breakout

Unicore UM982

The Unicore UM982 is a popular option for those that can’t cheaply access Ardusimple modules, or those who are looking to try out a WAS-less/integrated IMU system

Model options

The following models are suitable for standard AgOpenGPS systems:

The following models are NOT suitable, and should be avoided:

Configuration

Installation

Sample Suppliers

XBee module pinout

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If you match up the angled corners then the pinout matches, XBEE calls the communication pins DOUT/DIN instead of TX/RX. The only connections that the USB adapter makes is power, ground, DIN, DOUT, and RSSI (the led will just be off). Install with the RF connector away from the USB connector.

Note that the ArduSimple adapter doesn’t use the micro F9P’s USB connection, it uses the micro F9P’s serial connection through an FTDI converter. If you are going to use RTKBase for the base station then the micro F9P won’t be automatically recognized. You’ll want to jump to step 7 of the RTKBase Github install page “Connect your gnss receiver to raspberry pi/orange pi/… with usb or uart, and check which com port it uses (ttyS1, ttyAMA0, something else…)” Just a couple extra setup steps, not that time consuming.