Temporary RTK Express Base setup
Any tripod with a ¼” camera thread will work. The Amazon Basics tripod works well enough but is a bit light weight
and rickety. A cell phone holder is clamped to the tripod and the RTK Express is held in the clamp. The ¼” camera
thread is adapted to ⅝” 11-TPI and a L1/L2 antenna is attached. A Male TNC to Male SMA adapter connects the
antenna to the RTK Express.
Once the base has been setup with a clear view of the sky, turn on the RTK Express. Once on, press the Setup
button to put the device in Base mode. The display will show the Survey-In screen for 60-120 seconds. Once the
survey is complete the display will show the 'Xmitting' display and begin producing RTCM correction data. You can
verify this by viewing the LEDs on the telemetry radio (a small red LED will blink when serial data is received from
the RTK Express). The RTK Express is designed to follow the u-blox recommended survey-in of 60s and a mean
3D standard deviation of 5m of all fixes. If a survey fails to achieve these requirements it will auto-restart after 10
minutes.
More expensive surveyor bases have a ⅝” 11-TPI thread but the top of the surveyor base will often interfere with
the antenna’s TNC connector. If you chose to use a surveyor’s ‘stick’ be sure to obtain a ⅝” extender plate to raise
the antenna at least an inch.
If you’re shopping for a cell phone clamp be sure to get one that is compatible with the diameter of your tripod and
has a knob to increase clamp pressure. Our tripod is 18mm in diameter and we’ve had a good experience with this
clamp. Your mileage may vary.
Note: A mobile base station works well for quick trips to the field. However, the survey-in method is not
recommended for the highest accuracy measurements because the positional accuracy of the base will directly
translate to the accuracy of the rover. Said differently, if your base's calulcated position is off by 100cm, so will
every reading your rover makes. If you’re looking for maximum accuracy consider installing a static base with fixed
antenna. We were able to pinpoint the antenna on the top of SparkFun with an incredible accuracy +/-2mm of
accuracy using PPP!
Bluetooth and NTRIP
The RTK Express transmits full NMEA sentences over Bluetooth serial port profile (SPP) at 4Hz and 115200bps.
This means that nearly any GIS application that can receive NMEA data over serial port (almost all do) can be
used with the RTK Express. As long as your device can open a serial port over Bluetooth (also known as SPP)
your device can retrieve industry standard NMEA positional data. The following steps show how to use SW Maps
but the same steps can be followed to connect any serial port based GIS application.
The best mobile app that we’ve found is the powerful, free, and easy to use SW Maps by Softwel. You’ll need an
Android phone or tablet with Bluetooth. What makes SW Maps truly powerful is its built-in NTRIP client. This is a
fancy way of saying that we’ll be showing you how to get RTCM correction data over the cellular network. If you’re