U-box RTK gnss setup

Gidday All,

I hope everyone is having fun tinkering with new projects and prototypes.

I have a new project of my own which I am needing so assistance with.
I am wanting to build a prototype for get the vertical accuracy of a table’s height with RTK and gnss gps within a 10mm range. The task is to lift the table up and down with pitch and roll to see if it can accurately measure the different vertical heights of all 4 corners at the same time.

I would like to know if anyone has ever configured 4 u-box units with splitters to a single RTK ZED-F9P PCB which is then connected to a single IOT BT Raspberry Pi for data collection capabilities?
does each u-box require its own RTK ZED-F9P PCB to get the accuracy?
and is the splitter a multi-directional pcb or does it have one-way diodes?

Photos are attached of the components I would like to use.
If anyone has any recommendations to achieve the 10mm vertical accuracy I would love to hear what you have in mind.

Thank you


Hi Scott
Our GNSS Splitter (Power Divider) lets you connect a single GNSS antenna to two boards or modules. It splits (divides) the antenna signal from Port S equally between Port 1 and Port 2

I think that answers your question. This splits one antenna 2 ways to other devices. It seems to be active so probably one way.

Even if it did work the other way you would need 3 of these splitters for 4 antennas into one box and all you would be doing is mix all 4 signals resulting in something of a mess.

Is the GPS system that accurate vertically?
Cheers Bob


Hi Bob,

Perfect, thank you for that.
very helpful.
Just to confirm, so if I apply 2 u-box to a single splitter, connected the splitter to a ZED-F9P pcb and to the IOT Raspberry Pi then I should get 2 data readings of the vertical heights.


Does the Arduino Nano 33 IoT need a battery?
I can see it has an insert just about the u-box chip.


Hi Scott
Please read the above CAREFULLY this time. One input two outputs. As the name implies it is a splitter NOT a combiner. If it was passive it could well work both ways but it looks like an active device so probably one way.

Anyway if you did combine 2 sources how did you plan on separating them to retrieve the data.

By the way this is u-blox, not u-box. I had no idea what this is but it turns out it is the name of a company which makes GPS receivers among other things, u-box is a company that makes removalist containers… The RTK ZED-F9P as pictured seems to have one of these u-blox things on it so I don’t quite know where you are going. The black thing on the end of the cable is the GPS antenna, probably active as the splitter has DC pass through.
Cheers Bob


Hi Scott,

You should be able to use a single RTK system along with some clever math(and a 9-DOF IMU to figure out each of the heights of each corner.
Would it be possible to completely break down what the goal of your project is?

Another noteworthy point, will the project be running indoors? GPS signal is greatly affected by warehouse environments so might not be able to get the accuracy even with the base station.

Bob has you sorted out regarding the splitter and the working principal behind it.

The small shield just behind the U-Blox package is a Bluetooth antenna

Apparently so! With RTK active it is listed to down to 10mm for some of their other bundles! (Source)


1 Like

Hi Scott.
If it is just table pitch and roll you are after isn’t there some sort of sensor that will measure this?
I have a “Bubble Level” app on my phone which displays a central bubble and pitch and roll in degrees so there must be some sort of sensor inside that.
Just an alternative which may be simpler.
Cheers Bob

Hi Rob,

I’m actually wanting the use of this setup for it to get the stability of my boat at the front and back while I am floating in the water.

Hi Liam,

Sure, please see photo of what I am thinking could work for what I need.

What I ideally attempting to do is to see how much my boat moves up and down in the water when I load and unload my stuff.
I would love to be able to read the front and back height of my boat as it is moving up and down in the water from the vertical readings of the RTK.
I also would like to achieve the data collection coming from an IoT device straight to my phone, table or Laptop.
I did also place the 9-DOF IMU as you mention as this will be incredible useful if I can see the motion of the boat in 9 DoF as it moves.



Hi Scott.
I have said it all before.
That 3 port device is a SPLITTER. You have pictured it as a COMBINER. Combining 2 antenna signals to one output. Just the reverse of what it is designed to do.
Just how you were going to separate the 2 antenna signals in one receiver and get 2 separate lots of data is a bit beyond me and probably a lot of others. Please enlighten.
I believe those 2 black things are GPS antennas which do nothing but amplify a bit then pass the satellite signals to the receiver for processing.I believe you will need a separate receiver for each antenna. May be wrong but…

Don’t recollect mentioning anything like this, don’t even know what it is.
Cheers Bob

Hi Scott,

Liam and Robert are on the money here, RTK systems take one antenna signal, and output one position.

What you might want (for slightly more money) is a dead reckoning system, that in a single board, measures precise location with GNSS (and optionally RTK) as well as pitch, yaw and roll data with an IMU. It can fuse this data together when signal is bad to estimate where the vehicle is without any GPS data.

More info on what it can do out of the box here: