Real Time Kinematic (RTK) Basics

Real Time Kinematic positioning is a way to achieve 1-3 centimeters of accuracy using Global Navigation Satellite Systems (GNSS) or commonly referred to as GPS. GPS is specific to the satellite system established by the United States.

I’ve been dabbling with GNSS modules for a number of years. The accuracy with basic modules is usually around 3 meters which really isn’t bad to start with. However, the GPS you use in your car or phone knows what lane you are driving in. That of course requires a great degree of accuracy.

This blog is intended to be BASIC in nature. I’m not an expert. Yet. But I have learned some quick lessons that I want to pass on to anyone else wanting to dig into RTK.

SparkFun LG290P Quadband GNSS RTK

I’ve been messing with GPS modules for a while now. I’m always on the hunt for the best bang for the buck or the best learning tool. I recently stumbled across the Sparkfun LG290P Real Time Kinematic (RTK) GNSS board.

RTK has the ability to geo locate you to within 1 CENTIMETER of your location. Most GNSS modules net you about a 3 meter tolerance.

That is crazy accurate. Many of these RTK engines cost big $$$. This module is based on the Quectel LG290P engine. The good news is that it is lighter, cheaper, and runs cooler than most other RTK modules. Sparkfun sets the cost at $189 which is amazing.

GNSS200L GNSS Receiver Review

After digging through my GPS storage box I realized that I have never reviewed my GNSS200L GNSS receiver. I got mine at GPSWebShop a couple of years ago.

The advantage to this is that it is a puck and simply connects via USB to Windows, Linux, or MacOS.

There are no FTDI’s or serial converters needed. Just one clean USB connection to a computer.

Additionally, another major advantage is that because it is an authentic U-blox chip there is tons of documentation for it. If you buy some GPS module that is a knock off you aren’t going to get any documentation for it.

Adafruit Ultimate GPS USB – Best Bargain GPS

I love messing around with GPS modules. And I’ve said it before……..hooking a GPS up to a computer is a rite of passage for techies. I’m always on a quest to find a great module at a great price. Enter the Adafruit Ultimate GPS USB version ($29.99).

My favorite GPS modules are from U-blox however they tend to be a bit on the expensive side. That being said they have very powerful proprietary software that makes module configuration a breeze.

Not so much with the Adafruit modules which are based on the MTK3333 chipset which is definitely a great GPS chip. I know that you are thinking that you can buy GPS modules on Amazon or AliExpress for way less than $30, and you would be right. That being said almost ALL OF THEM are knock-offs and do not contain the chipsets that they claim. Yes, they are GPS modules, and yes, they work, however they are counterfeits mostly. I don’t like to spend my money on fakes.

Also places like Adafruit provide you tons of documentation to include command sheets, data sheets, and schematics. You get exactly what they say you get.

Choosing a GPS Module

I tend to believe that connecting a GPS module to a computer is a rite of passage for techies. While grabbing your exact coordinates and seeing it on a map is big fun it doesn’t compare to learning about GNSS or GPS systems.

Probably the most useful thing you can do with a GPS module in a home lab is to use it as a time server. Pulses Per Second or PPS is ridiculously accurate. You can achieve this in your home lab relatively cheap.

HiLetgo VK-172 USB GPS Review

U-blox 7020 in VK-172 GPS

I’m on a GPS kick lately and picked up a HiLetgo VK-172 GPS dongle ($12) from Amazon.

It claims to have a U-blox 7020 chipset inside but if I know anything it’s that most GPS modules you buy online that claim to be U-blox are usually counterfeit.

We might be in good shape here because the 7020 chipset is an older generation product according to U-blox.

The 7020 chipset is a GPS/GLONASS (Russian positioning system) and is small and low powered.  It is my understanding that it will not do GPS and GLONASS simultaneously.  You have to select one or the other in U-blox software.  United States GPS is a bit more accurate than GLONASS and it seems to be default set to GPS.  We’ll keep that setting for initial testing and toggle it to GLONASS later (if we can).

You can find these VK-172 GPS dongles all over the place but I think a large number of them have counterfeit chipsets.

Let’s test it with U-blox U-center software to see if it indeed an authentic chipset.
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USB GPS Receiver Uses

I have several blogs on GPS modules.  Most of them deal with either counterfeit modules or using a USB GPS module on an offline computer.

Then someone recently emailed me and asked,  “who the heck needs a USB GPS receiver”?  That is a perfectly good question to ask.   Most of us know right where we are, and besides, our phones and a lot of our cameras already have built in GPS.  While you know your phone has GPS and you can drop a pin to someone………when’s the last time you actually saw the coordinates?

And ask yourself if you can share that GPS with other devices on your network?
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GPS Linux GlobalSat Receiver Sirf Star IV Chipset

GlobalSat BU-353S4

This will be a quick primer on how to use a GlobalSat GPS receiver on Ubuntu Linux.

It is actually quite easy since Linux doesn’t need any drivers loaded.  Also this blog sort of augments the last blog I wrote  regarding the capabilities of using a computer offline.  In one section I used a U-blox GNSS module to capture GPS coordinates on Windows and Linux operating systems.

That U-blox module is not exactly what I’d consider to be weather proof.  My intent here is provide a GPS solution that is in some sort of reasonable enclosure that is more conducive to getting bounced around in a backpack.  Or more conducive to being used in an outdoor environment.
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