Two M2's sharing one LoRa Radio

Is it possible to connect two M2’s so they share corrections received by one LoRa radio? I am using two M2’s and two GNSS antennas to accurately determine direction, and I have two separate LoRa radios, but if I can get away with one it would be easier to install and allow me to have a backup radio. So essentially I am wondering if the M2’s can be daisy chained to share updates from the base?


Not if you are you talking about running a splitter off one antenna. They could share the single, but you would only get one location. Two antennas can share the same corrections stream though.

Not the best place to post this question I realize now.

I’ll answer my own question here; likely not, but it would be a nice design feature for the future. Either the M2 units are designed to share information through a hardware interface and software capability with this functionality in mind, or it is not. I suspect it is possible with some effort from the development side, possibly through software changes only without the need to make changes to hardware, but it would take some effort.

Emlid, please add the this functionality to the wish list.

Like I said it depends on the context of which your question lies. If you are talking about a single antenna then you are doing this for redundancy. Determining heading requires individual points of reference. If your are trying to feed the positional information to another app or piece of equipment then you will want a controller in between that can utilize the data independently. For instance in machine control there is a controller box that feeds the individual positions to specific pieces of hardware or in conjunction with another sensor feeds a software platform for feedback.

The M2’s are obviously designed as modules to aid this activity and not to perform it themselves so I would say no this functionality is not natively designed for. Every situation is going to be different according to the specifications of the hardware used.

Hi Michael,
I appreciate your help with this. The objective is to use two precise RTK positions from two GNSS antennas and two M2 recievers to determine a static orientation. An IMU/ MEM using the earth’s magnetic field is not precise enough for my purposes. Again, I am not using one GNSS antenna, but two, one for each M2.

The M2’s find a RTK solution by using corrections derived from the RTCM3 messages transmitted from the base, and received through the LoRa radio. The real question for me is how does the M2 communicate with the LoRa Radio, and how to share messages from the LoRa radio with the second M2 receiver? My original question was if the M2’s were designed with this in mind, but as we both suspect, it likely is not, otherwise it would be a selling point and documentation on that capability would exist. The only way to to make it work would be to have some TTL logic or more likely a micro-controller between the LoRa radio and the individual M2’s to manage the communication, but then I would have to reverse engineer the communication protocols and I’m not going to get into that at the moment. The easiest thing for me to do is install the second radio as planned and hope Emlid puts some effort into providing this functionality in the future.

Thanks again for your help,

Both M2’s should be able to receive corrections from a single base. The determination I was trying to make was what were the expectations for the data output from the M2’s. Indeed we assume that the output is designed for event and position based data. The mention of the controller as you stated is to then use that data to perform another function in the workflow.

Right, both M2’s can receive corrections from a single base, but through the same LoRa reciever? That’s the question. The management of the positional solutions from each M2 is not relevant to my question. But if you are simply curious, I am planning to use a RaspberryPi 3 A+ to integrate peripherals and the two RTK GGA NMEA streams over UART. I havn’t got the ERB packet structure figured out just yet, there doesn’t seem to be a lot of documentation on that. I want to avoid communication by bluetooth as that will give out over time, and the fact that separate aluminum project boxes are being used to install the electronics. Do you have experience with using the ERB packet structure?

I can’t think of a reason why the corrections couldn’t be split. The stream is from a single source and the M2’s have independent chips and antenna so unless there is a line quality issue from the split it should work just fine.

The connection from the M2 to the LoRa radio looks to use UART along with several GPIO connections (S2 connector on the M2). If you think about it, the M2 has to set the frequency monitored by the LoRa radio, so it is not just a matter of splitting the communication line, there will be binary protocols to control the flow of information.

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Honestly, I think in order to get an accurate heading using both units, both will need LoRa radios and be set up on an accurate known baseline lengths maybe 1’ foot apart using same kind of antennas.
Then the fun can start.

You’ll probably have to talk with Emlid using their proprietary commands accessing the ports of the M2’s. If you could get both units to send out a NMEA stream to a Raspberry Pi unit or even a handheld computer, you’d have most of the problem solved.
Then it be a simply matter of programming in possibly C language to get the data you need.

Seems like a fun project. In my younger days, I thought I was pretty proficient in C. I programmed many survey routines in a handheld MC-V and even got the data out of survey total stations using their data streams as most instruments had the info in their manuals.

It’s a shame they’re isn’t a program manual for the M2. There’s a lot of possibilities for the M2 if Emlid would provide communication protocols.

Thanks Bryan,
My GNSS antennas are 0.75’ apart, It gives me an acceptable error for my purposes assuming a 3mm error when fixed. Isn’t it great that this gear is available at a price point that is accessible? If I tried to construct my project ten years ago it would be four to five times the size and weight and easily 12x the cost. Then there is the RaspberryPi and all the available microelectronics, sensors, IMU’s, LiDAR, it is just such an exciting time to tinker.

Thanks again for your input, I’ll have to dog Emlid for better documentation on their binary protocol. I’ve looked through the forum a few times and did not find very much other than the white sheet that demonstrates the basic packet structure. Nothing on registries that can be PEEKED and POKED, or even if that is how it works. I should be able to get to it in a week or so, I’ve got a few irons in the fire.
Take Care,

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Obviously the further apart you can get them the better. What’s it for? I guess my assumption of something like a tractor or a boat was a little big. Many machines with GPS control had one radio feeding two controllers for a long time. Now most use IMU’s and rotation sensors in addition.

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Yep, if you could only get through to the Ublox chip, you could use Ublox commands for the output streams. That’s the key to your development. Keep us posted on your project Tyler, it’s a really neat project you have. I wish I had more time to do stuff like this !!

You’ve probably seen this site, they have a lot of neat gadgets like this, cost is pretty reasonable compared to Emlid’s and has the same Ublox chip I think and you can access the documented Ublox commands

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two (m2)rover in one pole?

Yep you could do that but I think it would be kind of cumbersome. Javad use to sell a unit with three antennas and it had a wheeled mount on the survey rod. It actually computed a baseline between the antennas to verify the actual survey point. Pretty neat

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I have seen a similar setup with Topcon. The main advantage was on Excavators and Vehicles. It tracked heading better, but it was also faster and able to keep up with the 1000Hz feed to the control box creating a smoother reaction from the machine.

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Hi Tyler,

Welcome to our community!

Thank you for the feature request. You are right, Reach rovers can’t share corrections in the way you described at the moment.

If it’s appropriate for you, you can provide base corrections to the rovers using our NTRIP caster. In such a setup, you don’t need to attach LoRa radio modules to Reach M2. Please note that all the units need Internet access to use NTRIP.

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