2024-03-12 | By SparkFun Electronics

License: See Original Project GPS USB Wifi ESP32

Courtesy of SparkFun

Guide by NATE

Introduction

The RTK Facet L-Band from SparkFun is our most advanced GNSS receiver to date. It's your one ‎stop shop for high precision geolocation and surveying needs. For basic users, it’s incredibly easy ‎to get up and running and for advanced users, the RTK Facet L-Band is a flexible and powerful tool.‎

SparkFun RTK Facet L-Band

With just a few minutes of setup, the RTK Facet L-Band is the fastest product currently on the ‎market to take centimeter grade measurements.‎

Surveying with a monopod and SW Maps

An RTK Fix with 14mm accuracy in SW Maps

With just the press of a button, the RTK Facet L-Band is the fastest way to take centimeter-grade ‎measurements. With built-in corrections, 14mm Real Time Kinematic fixes are less than a minute ‎away. By connecting your phone to the RTK Facet L-Band over Bluetooth®, your phone or tablet ‎can receive the NMEA output and work most GIS software. This is exactly how $10,000 surveying ‎devices have been operating for the past decade - we just made it faster, more precise, and a lot ‎more economical.‎

Required Materials

The RTK Facet L-Band has all you need built into one small unit. In addition, the RTK Facet L-Band ‎Kit includes everything you might need as well. The only thing you need to add is your own tablet ‎or cell phone (currently Android is supported; iOS support planned).‎

No external radio link or RTCM corrections are needed. The RTK Facet L-Band utilizes corrections ‎from u-blox's PointPerfect service broadcast from a geosynchronous Inmarsat satellite. The only ‎setup required is a WiFi SSID and password. Once entered, the device will provision itself and ‎periodically (once a month) update the decryption keys necessary to use the PointPerfect service. ‎The price of the RTK Facet L-Band includes a 12-month subscription. Additional years of service ‎can be purchased.‎

To charge the RTK Facet you will need a USB C cable and a power supply. These are included with ‎the kit, but any USB C port should charge the Facet at a maximum rate of 1A per hour.‎

• USB 2.0 Type-C Cable - 1 Meter
• ‎Reversible USB A to C Cable - 0.8m‎
• USB-C Wall Adapter - 5.1V, 3A (Black)
• ‎USB Wall Charger - 5V, 2A‎

Suggested Reading

GNSS RTK is an incredible feat of engineering that has been made easy to use by powerful GNSS ‎receivers such as the ZED-F9P by u-blox (the receiver inside RTK Facet). The process of setting ‎up an RTK system will be covered in this tutorial but if you want to know more about RTK here are ‎some good tutorials to brush up on:‎

• What is GPS RTK? Learn about the latest generation of GPS and GNSS receivers to get 14mm ‎positional accuracy!‎
• Getting Started with U-Center for u-blox: Learn the tips and tricks to use the u-blox ‎software tool to configure your GPS receiver.‎
• GPS-RTK2 Hookup Guide: Get precision down to the diameter of a dime with the new ZED-‎F9P from u-blox.‎
• Setting up a Rover Base RTK System: Getting GNSS RTCM correction data from a base ‎to a rover is easy with a serial telemetry radio! We'll show you how to get your high precision RTK ‎GNSS system setup and running.‎
• How to Build a DIY GNSS Reference Station: Learn how to affix a GNSS antenna, use ‎PPP to get its ECEF coordinates and then broadcast your own RTCM data over the internet and ‎cellular using NTRIP to increase rover reception to 10km!‎

How RTK Facet L-Band Works

The SparkFun RTK Facet L-Band is unique in that it receives its corrections from u-blox's ‎PointPerfect service broadcast from a geosynchronous Inmarsat satellite. No base station is needed, ‎no external radio link, no internet connection or RTCM corrections are needed to achieve RTK fix. ‎The RTK Facet L-Band does not require creating an account anywhere, does not require copy and ‎pasting of keys, certificates, or any other materials. Everything is built into one unit and made to be ‎as easy as possible to use.‎

What magic is this?‎

A normal RTK setup requires a Base and Rover. The Base sits still and provides RTCM corrections ‎over a radio or internet link to a rover. These corrections aid the Rover in its location calculations ‎allowing it to remove small ionospheric and tropospheric distortions. When it's all working, you can ‎achieve 14mm X, Y, and Z accuracy. For many applications this works fine, but for a variety of ‎applications a unit is often located far from cellular connectivity, or a base station setup is not ‎possible. For this reason, u-blox has built a large network of base stations across the contiguous 48 ‎states of the USA and the EU. The correction data from these stations are aggregated into a series ‎of correction feeds. Those feeds are then uplinked to, and broadcast from, a geosynchronous ‎satellite operated by another company call Inmarsat. In the USA, the satellite is broadcasting at ‎‎1.55629GHz and in Europe a different Inmarsat is broadcasting at 1.54526GHz. These frequencies ‎are handy in that they are in the same band as the GNSS satellites: L-Band. L-Band is any ‎frequency from 1 to 2 GHz. These frequencies have the ability to penetrate clouds, fog, and other ‎natural weather phenomena making them particularly useful for location applications.‎

The single antenna atop the RTK Facet L-Band is a unique combination of elements designed to ‎receive the GNSS signals (L1/L2) alongside the 1.55GHz PointPerfect corrections. These signals ‎are sent to the ZED-F9P for classic GNSS position calculation (e.g., producing latitude, longitude, ‎and altitude of the device), and to the NEO-D9S. The NEO-D9S is a satellite receiver whose sole ‎purpose is to be tuned to a frequency (in our case ~1.55GHz) and output data. This data is the ‎encrypted correction data in the SPARTN format. The RTK Facet L-Band receives these packets ‎and passes them to the ZED-F9P. At startup, the ESP32 provides the ZED-F9P with decryption ‎keys. With the packets and the keys, the ZED-F9P is able to decrypt the data and use it to correct ‎its GNSS fix allowing the accuracy to increase from ~300mm to the RTK accuracy of 10 to 20mm.‎

It is fun to point out the GNSS satellites have a medium earth orbit, circling the earth every 12 hours, ‎and have an orbit above the earth at approximately 22,200 kilometers (12,551 miles). Whereas the ‎Inmarsat satellites broadcasting the PointPerfect correction values at ~1.5GHz are geosynchronous ‎and therefore must be located much further out, at about 35,786 kilometers (22,236 miles.)‎

Where can the RTK Facet L-Band operate?‎

USA and EU Coverage Map of PointPerfect Corrections

Currently the u-blox PointPerfect service is only offered for the USA's contiguous 48 states and the ‎EU. Please see u-blox website for additional information. If L-Band coverage is not available in your ‎area, the RTK Facet L-Band is still capable of better than 300mm accuracy off the shelf and 14mm ‎accuracy when provided RTCM corrections using a standard Base/Rover setup.‎

How much does this cost?‎

The cost of a RTK Facet L-Band includes a 12-month subscription to u-blox's PointPerfect L-Band ‎service. u-blox does not currently offer PointPerfect L-Band service to individuals. SparkFun ‎formed a partnership with u-blox to allow SparkFun users to obtain L-Band service through ‎SparkFun's account.‎

How do the 'keys' work?‎

One of our mantras at SparkFun is Don't Make Me Think based on a book by Steve Krug. The RTK ‎Facet L-Band does not require creating an account anywhere, does not require copy and pasting of ‎keys, certificates, or any other materials. The provisioning process is complicated, so we've ‎designed the firmware within the RTK Facet L-Band to deal with everything. The only thing a user ‎must provide is a 'Home' WiFi network ID and password. We use the term 'Home' but it is the ‎network the device is mostly likely to be turned on around, for example the surveyor's office, ‎school, or residence. Once these details are entered via WiFi or serial, the device will take care of ‎everything else.‎

How do the L-Band keys work?‎

The correction data that is broadcast via Inmarsats is encrypted. The decryption keys expire every ‎‎28 days, and two keys are provided during each update process. This means the RTK Facet L-‎Band can operate without any internet connectivity for a maximum of 56 days best case, 29 days ‎worst case. Every time the device is powered on the RTK Facet L-Band will attempt to connect to its ‎‎'Home' WiFi. If successful, the keys will automatically be updated and stored. The whole process ‎takes less than 10 seconds (worst case). The RTK Facet L-Band will show a series screens ‎indicating what it’s doing but the device is designed to be used without concern or supervision.‎

What happens after 12 months?‎

The retail price of the RTK Facet L-Band includes 12 months of PointPerfect corrections. After 12 ‎months the device will be unable to obtain keys and the device will operate as a normal, very high ‎accuracy GNSS receiver. If additional PointPerfect corrections are needed they can be purchased ‎for $500 per year by contacting SparkFun customer service.‎

Can I get a unit without the subscription?‎

u-blox does not currently offer PointPerfect L-Band service to individuals. If you are interested in ‎purchasing a large number of RTK Facet L-Bands, we can work with you to provide subscription-‎less units, but it is up to your organization to confirm that L-Band service will be provided. The RTK ‎Facet L-Band allows for a custom Device Profile Token. Once you have an account setup with u-‎blox, this token will need to be entered into all RTK Facet L-Band devices and they can provision ‎through the normal PointPerfect API. Please contact SparkFun customer service for more ‎information.‎

What are the down sides to L-band corrections?‎

Cons:‎

• RTK fix time using L-Band is 45 to 60 seconds as opposed to RTCM based RTK which can ‎take a few seconds.
• Increased cost via subscription fees to u-blox.‎
• Accuracy varies from 30 to 60mm guaranteed with 14 to 20mm regularly seen.‎

Pros:‎

• High precision RTK fixes without any setup.
• Very easy to setup and just use. No base, no radio, no internet needed.‎

Hardware Overview

The RTK Facet L-Band is a fully enclosed, preprogrammed device. There are very few things to ‎worry about or configure but we will cover the basics.‎

Power/Setup Button

The RTK Facet L-Band has one button used for both Power and Setup for in-field configuration ‎changes. Pressing and holding the Power button will cause it to power on or off. Short pressing the ‎button will cause the RTK Facet L-Band to change modes.‎

This device can be used in five modes:‎

• GNSS Positioning (~30cm accuracy) - also known as 'Rover'‎
• GNSS Positioning with RTK L-Band (1.4 to 6cm accuracy) - also known as 'Rover with L-Band ‎RTK Fix'
• GNSS Positioning with RTK (1.4cm accuracy) - also known as 'Rover with RTK Fix'‎
• GNSS Base Station
• GNSS Base Station NTRIP Server

At Power On the device will enter Rover or Base mode; whichever state the device was in at the last ‎power down. When the POWER/SETUP button is pressed momentarily, a menu is presented to ‎change the RTK Facet L-Band to Rover or Base mode. The display will indicate the change with a ‎small car or flag icon.‎

In Rover mode the RTK Facet L-Band will check if WiFi is available and update any L-Band keys ‎needed (keys expire every 56 days). The device will automatically begin receiving and decrypting ‎position correction data. Simultaneously, the RTK L-Band will receive L1 and L2 GNSS signals from ‎the four constellations (GPS, GLONASS, Galileo, and BeiDou). The device will calculate the ‎position based on the combination of GNSS and correction signals. The receiver will quickly (within ‎‎60 seconds) obtain an RTK float, then fix. Similar to a standard grade GPS receiver, the RTK Facet ‎L-Band will output industry standard NMEA sentences at 4Hz and broadcast them over any paired ‎Bluetooth® device. The end user will need to parse the NMEA sentences using commonly available ‎mobile apps, GIS products, or embedded devices (there are many open-source libraries). Unlike ‎standard grade GPS receivers that have 2500mm accuracy, the accuracy in this mode is ‎approximately 14 to 60mm horizontal positional accuracy.‎

If the device is in Rover mode but L-Band is not available, regular RTCM based RTK is still available. ‎When RTCM correction data is sent over Bluetooth® or into the radio port, the device will ‎automatically enter Positioning with RTK mode. In this mode RTK Facet L-Band will receive L1/L2 ‎signals from the antenna and correction data from a base station. The receiver will quickly (within a ‎second) obtain an RTK float, then fix. The NMEA sentences will have increased accuracy of 14mm ‎horizontal and 10mm vertical accuracy. The RTCM correction data is most easily obtained over the ‎Internet using a free app on your phone (see SW Maps or Lefebure NTRIP) and sent over ‎Bluetooth® to the RTK Facet L-Band but RTCM can also be delivered over an external cellular or ‎radio link to a 2nd RTK Facet, Surveyor, Express, etc., setup as a base station.‎

In Rover mode the RTK Facet L-Band will receive L1 and L2 GNSS signals from the four ‎constellations (GPS, GLONASS, Galileo, and BeiDou) and calculate the position based on these ‎signals. Similar to a standard grade GPS receiver, the RTK Facet L-Band will output industry ‎standard NMEA sentences at 4Hz and broadcast them over any paired Bluetooth® device. The end ‎user will need to parse the NMEA sentences using commonly available mobile apps, GIS products, ‎or embedded devices (there are many open-source libraries). Unlike standard grade GPS receivers ‎that have 2500mm accuracy, the accuracy in this mode is approximately 300mm horizontal positional ‎accuracy.‎

In Base mode the device will enter Base Station mode. This is used when the device is mounted to ‎a fixed position (like a tripod or roof). The RTK Facet L-Band will initiate a survey. After 60 to 120 ‎seconds the survey will complete and the RTK Facet L-Band will begin transmitting RTCM ‎correction data out the radio port. A base is often used in conjunction with a second RTK Facet L-‎Band (or RTK Surveyor, Express, Express Plus, etc.) unit set to 'Rover' to obtain the 14mm ‎accuracy. Said differently, the Base sits still and sends correction data to the Rover so that the ‎Rover can output a really accurate position.‎

Power‎

RTK Facet L-Band startup display with firmware version number

The Power button turns on and off the unit. Press and hold the power button until the display ‎illuminates. Press and hold the power button at any time to turn the unit off.‎

RTK Facet L-Band showing the battery level

The RTK Facet L-Band has a large, built-in 6000mAh lithium polymer battery that will enable over 25 ‎hours of field use between charging. If more time is needed a common USB power bank can be ‎attached boosting the field time to any amount needed.‎

Charge LED

The Charge LED is located on the front face. It will illuminate any time there is an external power ‎source and will turn off when the internal battery is charged. With the unit fully powered down, ‎charging takes approximately 6 hours from a 1A wall supply or 12 hours from a standard USB port. ‎The RTK Facet L-Band can run while being charged but it increases the charge time. Using an ‎external USB battery bank to run the device for extended periods or running the device on a ‎permanent wall power source is supported.‎

Connectors

The SparkFun RTK Facet L-Band connectors shown with the dust cover removed

There are a variety of connectors protected by a dust flap.‎

USB

This USB C connector is used for four purposes:‎

• Charging the device
• Configuring the RTK Facet L-Band, and reprogramming the ESP32
• Updating the firmware of the ZED-F9P as needed
• Updating the firmware of the NEO-D9S as needed

There is a USB hub built into the RTK Facet L-Band. When you attach the device to your computer ‎it will enumerate as three COM ports.‎

In the image above, the USB-SERIAL CH340 is the ESP32, and the USB Serial Device is the ZED-‎F9P and the NEO-D9S.‎

Don't See 'USB-Serial CH340'? If you've never connected a CH340 device to your computer ‎before, you may need to install drivers for the USB-to-serial converter. Check out our section ‎on "How to Install CH340 Drivers" for help with the installation.‎

Don't See 'USB Serial Device'? The first time a u-blox module is connected to a computer you ‎may need to adjust the COM driver. Check out our section on "How to Install u-blox Drivers" for ‎help with the installation.‎

Configuring the RTK Facet L-Band can be done over the USB-Serial CH340 COM port via serial ‎text menu. Various debug messages are printed to this port at 115200bps, and a serial menu can ‎be opened to configure advanced settings. Configuring the ZED-F9P can be configured over ‎the USB Serial Device port using u-center. It’s not necessary in normal operation but is handy for ‎tailoring the receiver to specific applications. As an added perk, the ZED-F9P can be detected ‎automatically by some mobile phones and tablets. If desired, the receiver can be directly connected ‎to a compatible phone or tablet removing the need for a Bluetooth connection.‎

Radio

This port is used when an external cellular or radio link is needed. This port is not used if you ‎transfer RTCM from your phone to the RTK Facet L-Band over Bluetooth.‎

This 4-pin JST connector can be used to allow RTCM correction data to flow into the device when it ‎is acting as a rover or out of the device when it is acting as a base. The connector is a 4-pin locking ‎‎1.25mm JST SMD connector (part#: SM04B-GHS-TB, mating connector part#: GHR-04V-S.) The ‎RTK Facet L-Band comes with a cable to interface to this connector but additional cables can be ‎purchased. You will most likely connect this port to one of our Serial Telemetry Radios if you don’t ‎have access to a correction source on the internet. The pinout is 3.5-5.5V / TX / RX / GND from left ‎to right as pictured. 3.5V to 5.5V is provided by this connector to power a radio with a voltage that ‎depends on the power source. If USB is connected to the RTK Facet L-Band then voltage on this ‎port will be 5V (+/-10%). If running off of the internal battery, then voltage on this port will vary with ‎the battery voltage (3.5V to 4.2V depending on the state of charge). This port is capable of ‎sourcing up to 600mA and is protected by a PTC (resettable fuse.) This port should not be ‎connected to a power source.‎

Data

This port is used when an external system is connected such as a rover, car, timing equipment, ‎camera triggers, etc. This port is not used if you transfer NMEA positional data to your phone from ‎the RTK Facet L-Band over Bluetooth.‎

This 4-pin JST connector is used to output and input a variety of data to the RTK Facet L-Band. ‎The connector is a 4-pin locking 1.25mm JST SMD connector (part#: SM04B-GHS-TB, mating ‎connector part#: GHR-04V-S). The RTK Facet L-Band comes with a cable to interface to this ‎connector but additional cables can be purchased.‎

Internally the Data connector is connected to a digital mux allowing one of four software selectable ‎setups. See the Ports Menu for a description of each option:‎

• NMEA - The TX pin outputs any enabled messages (NMEA, UBX, and RTCM) at a default of ‎‎460,800bps (configurable 9600 to 921600bps). The RX pin can receive RTCM for RTK and ‎can also receive UBX configuration commands if desired.‎
• PPS/Trigger - The TX pin outputs the pulse-per-second signal that is accurate to 30ns RMS. ‎The RX pin is connected to the EXTINT pin on the ZED-F9P allowing for events to be ‎measured with incredibly accurate nano-second resolution. Useful for things like audio ‎triangulation.
• I²C - The TX pin operates as SCL, RX pin as SDA on the I2C bus. This allows additional ‎sensors to be connected to the I2C bus.
• GPIO - The TX pin operates as a DAC capable GPIO on the ESP32. The RX pin operates as a ‎ADC capable input on the ESP32. This is useful for custom applications.‎

Most applications do not need to utilize this port and will send the NMEA position data over ‎Bluetooth. This port can be useful for sending position data to an embedded microcontroller or ‎single board computer. The pinout is 3.3V / TX / RX / GND. 3.3V from left to right as pictured, ‎which is provided by this connector to power a remote device if needed. While the port is capable ‎of sourcing up to 600mA, we do not recommend more than 300mA. This port should not be ‎connected to a power source.‎

microSD

This slot accepts standard microSD cards up to 32GB formatted for FAT16 or FAT32. Logging any ‎of 67 messages at up to 4Hz is supported for all constellations.‎

The following 67 messages are supported for logging:‎

Qwiic

This 4-pin Qwiic connector exposes the I2C bus of the ESP32 WROOM module. Currently, there is ‎no firmware support for adding I²C devices to the RTK Facet L-Band, but support may be added in ‎the future.‎

Antenna

It's built in! Housed under the dome of the RTK Facet L-Band is a surveyor grade L1/L2/L-Band ‎antenna. This antenna is a unique combination of elements designed to receive the GNSS signals ‎‎(L1/L2) alongside the 1.55GHz PointPerfect corrections. The built-in antenna has an ARP of 69mm ‎from the base to the measuring point of the L1 antenna and an ARP of 68mm to the measuring ‎point of the L2 antenna.‎

SparkFun RTK Facet L-Band Antenna Reference Points

The built in antenna has an ARP of 61.4mm from the base to the measuring point of the L1 antenna ‎and an ARP of 57.4mm to the measuring point of the L2 antenna.‎

Power

RTK Facet L-Band Display showing three battery bars

The RTK Facet L-Band has a built in 6000mAh battery and consumes approximately 240mA worst ‎case with Bluetooth connection active and GNSS fully tracking. This will allow for around 25 hours ‎of use in the field. If more time is needed in the field a standard USB power bank can be attached. ‎If a 10,000mAh bank is attached one can estimate 56 hours of run time assuming 25% is lost to ‎efficiencies of the power bank and charge circuit within RTK Facet L-Band.‎

The RTK Facet L-Band can be charged from any USB port or adapter. The charge circuit is rated ‎for 1000mA so USB 2.0 ports will charge at 500mA and USB 3.0+ ports will charge at 1A.‎

To quickly view the state of charge, turn on the unit. The battery icon will indicate the following:‎

• ‎3 bars: >75% capacity remain
• ‎2 bars: >50% capacity remain‎
• ‎1 bar: >25% capacity remain
• ‎0 bars: <25% capacity remain

Hardware Overview - Advanced Features

The boards that make up the RTK Facet L-Band

The RTK Facet L-Band is a hacker’s delight. Under the hood of the RTK Facet L-Band is an ESP32 ‎WROOM connected to a ZED-F9P as well as some peripheral hardware (LiPo fuel gauge, microSD, ‎etc.) It is programmed in Arduino and can be tailored by the end user to fit their needs.‎

The Facet L-Band Main Board

ZED-F9P GNSS Receiver

The ZED-F9P GNSS receiver is configured over I²C and uses two UARTs to output NMEA (UART1) ‎and input/output RTCM (UART2). In general, the ESP32 harvests the data from the ZED-F9Ps ‎UART1 for Bluetooth transmission and logging to SD.‎

NEO-D9S L-Band Receiver

The NEO-D9S is configured over I²C. The ESP32 sends decryption keys to the ZED-F9P at startup ‎then harvests the encrypted PMP data from the NEO-D9S and sends the packets to the ZED-F9P ‎over I²C.‎

ESP32‎

The ESP32 uses a standard USB to serial conversion IC (CH340) to program the device. You can ‎use the ESP32 core for Arduino or Espressif’s IoT Development Framework (IDF).‎

The CH340 automatically resets and puts the ESP32 into bootload mode as needed. However, the ‎reset pin of the ESP32 is brought out to an external 2-pin 0.1” footprint if an external reset button is ‎needed.‎

Note: If you've never connected a CH340 device to your computer before, you may need to install ‎drivers for the USB-to-serial converter. Check out our section on "How to Install CH340 Drivers" for ‎help with the installation.‎

LiPo and Charging

The RTK Facet L-Band houses a standard 6000mAh 3.7V LiPo. The charge circuit is set to 1A so ‎with an appropriate power source, charging an empty battery should take a little over six hours. USB ‎C on the RTK Facet L-Band is configured for 2A draw so if the user attaches to a USB 3.0 port, the ‎charge circuit should operate near the 1A max. If a user attaches to a USB 2.0 port, the charge ‎circuit will operate at 500mA. This charge circuit also incorporates a 42C upper temperature cutoff ‎to insure the LiPo cannot be charged in dangerous conditions.‎

Fuel Gauge and Accelerometer

The MAX17048 is a simple to use fuel gauge IC that gives the user a statement of charge (SOC) ‎that is basically a 0 to 100% report. The MAX17048 has a sophisticated algorithm to figure out what ‎the SOC is based on cell voltage that is beyond the scope of this tutorial but for our purposes, ‎allows us to reliably view the battery level when the unit is on.‎

The RTK Facet L-Band also incorporates a the LIS2DH12 triple-axis accelerometer to aid in leveling ‎in the field.‎

Qwiic

An internal Qwiic connector is included in the unit for future expansion. Currently the stock RTK ‎Facet L-Band does not support any additional Qwiic sensors or display, but users may add support ‎for their own application.‎

microSD

A microSD socket is situated on the ESP32 SPI bus. Any microSD up to 32GB is supported. RTK ‎Facet L-Band supports RAWX and NMEA logging to the SD card. Max logging time can also be set ‎‎(default is 24 hours) to avoid multi-gigabyte text files. For more information about RAWX and doing ‎PPP please see this tutorial.‎

Data Port and Digital Mux

The 74HC4052 analog mux controls which digital signals route to the external Data port. This allows ‎a variety of custom end user applications. The most interesting of which is event logging. Because ‎the ZED-F9P has microsecond accuracy of the incoming digital signal, custom firmware can be ‎created to triangulate an event based on the receiver's position and the time delay between multiple ‎captured events. Currently, TM2 event logging is supported.‎

Additionally, this mux can be configured to connect ESP pin 26 (DAC capable) and pin 39 (ADC ‎capable) for end user custom applications.‎

Hardware Assembly

The RTK Facet L-Band was designed to work with low-cost, off the shelf equipment. The RTK ‎Facet L-Band is designed to use corrections provided via u-blox's PointPerfect system, therefore, a ‎Base/Rover setup is not needed. However, if the service is not available the RTK Facet L-Band can ‎still be used in a traditional Base/Rover setup. Here we’ll describe how to assemble a Rover and ‎Base.‎

Surveying (Rover Mode)‎

Basic RTK Facet L-Band Rover setup with RTCM over Bluetooth

Shown above is the most common RTK Rover setup. A monopole designed for cameras is used. ‎The ¼” camera thread of the monopole is adapted to ⅝” 11-TPI and the RTK Facet L-Band is ‎mounted on top. No radio is needed because RTCM correction data is provided by a phone over ‎Bluetooth.‎

If you’re shopping for a monopole (aka monopod), get one that is 65” in length or greater to ensure ‎that the antenna will be above your head. We’ve had good luck with the Amazon Basics brand.‎

If you prefer to mount your tablet or cell phone to the monopole, be sure to get a clamp that is ‎compatible with the diameter of your monopole and has a knob to increase clamp pressure. Our ‎monopole is 27mm in diameter so a device clamp would need to be able to handle that diameter.‎

2nd most common setup with a 915MHz Radio providing RTCM‎

If you are receiving RTCM correction data over a radio link it’s recommended that you attach a radio ‎to the bottom of the RTK Facet L-Band.

Picture hanging strips from 3M make a nice semi-permanent mount. Plug the 4-pin to 6-pin JST ‎cable included with the RTK Facet L-Band from the Radio port to either of the Serial Telemetry ‎Radios (shipped in pairs). We really love these radios because they are paired out of the box, either ‎can send or receive (so it doesn't matter which radio is attached to base or rover) and they have ‎remarkable range. We achieved over a mile range (nearly 1.5 miles or 2.4km) with the 100mW ‎radios and a big 915MHz antenna on the base (see this tutorial for more info.)‎

Temporary Base

A temporary or mobile base setup is needed when you are in the field too far away from a ‎correction source and/or cellular reception. A 2nd RTK Facet L-Band is mounted to a tripod, and it ‎is configured to complete a survey-in (aka, locate itself), then begin broadcasting RTCM correction ‎data. This data (~1000 bytes a second) is sent to the user's connected radio of choice. For our ‎purposes, the 915MHz 100mW telemetry radios are used because they provide what is basically a ‎serial cable between our base and rover.‎

Temporary RTK Facet L-Band 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. The ¼” camera thread is adapted to ⅝” 11-TPI and the RTK Facet L-‎Band is attached on top.‎

Once the base has been setup with a clear view of the sky, turn on the RTK Facet L-Band. 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 Facet L-Band). The RTK ‎Facet L-Band 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.‎

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 calculated ‎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 Facet L-Band 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 Facet L-Band. 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.‎

Please see the SparkFun RTK Product Manual for step-by-step instructions.‎

Display

The RTK Facet L-Band has a 0.96" high-contrast OLED display. While small, it packs various ‎situational data that can be helpful in the field. Please see the SparkFun RTK Product Manual for a ‎description of each display.‎

System Configuration

Out of the box, the SparkFun RTK products are exceptional GNSS receivers out-of-box and can be ‎used with little or no configuration. Additionally, the line of RTK products from SparkFun are ‎immensely configurable. Please see the SparkFun RTK Product Manual for detailed descriptions of ‎all the available features on the RTK products.‎

Firmware Updates and Customization

The RTK Facet is open source hardware meaning you have total access to ‎the firmware and hardware.‎

From time-to-time SparkFun will release new firmware for the RTK product line to add and improve ‎functionality. We've made updating the firmware as easy as possible. Please see Updating RTK ‎Firmware for a step-by-step tutorial.‎

Troubleshooting

Not working as expected and need help? ‎

If you need technical assistance and more information on a product that is not working as you ‎expected, we recommend heading on over to the SparkFun Technical Assistance page for some ‎initial troubleshooting.

SPARKFUN TECHNICAL ASSISTANCE PAGE‎ ‎

If you don't find what you need there, the SparkFun Forums are a great place to find and ask for ‎help. If this is your first visit, you'll need to create a Forum Account to search product forums and ‎post questions.

CREATE NEW FORUM ACCOUNT     LOG INTO SPARKFUN FORUMS

Resources and Going Further

We hope you enjoy using the RTK Facet L-Band as much as we have!‎

Here are the pertinent technical documents for the RTK Facet L-Band:‎

• RTK Product Manual
• ZED-F9P Datasheet
• NEO-D9S Datasheet
• MAX17048 Fuel Gauge IC
• SparkFun RTK Facet GitHub Repo (contains the open-source hardware electronics and ‎enclosure)
• ‎SparkFun RTK Firmware GitHub Repo (contains the firmware that runs SparkFun RTK ‎products)