Moving from M+ to M2 - Will it solve my issues?

Hi all,

We have successfully integrated the M+ and RS+ on our drone using RDF900 as a link between both. It works well for certain cases, but we are having lots of trouble acquiring fix and maintaining it in wooded areas, as one would expect.
We are considering upgrading to the M2/RS2 receivers as they have a better capacity of getting lock on satellites through thick canopy and accelerate fix acquisition. This would be quite a big purchase and I would like to get some info first:

  1. Our work is always done in wooded areas, often in tight spaces with about 45 degrees sky visibility, will L2 receivers really improve fix acquisition?

  2. Does L2 imply a heavier use of bandwidth on the RFD900 radios or is it the same as L1? We fear that the addition of more corrections might overload the outgoing signal.

Thanks a lot!

The multi-path receivers will definitely improve your situation. What kind of antenna do you have on the RFD900? When we get in tough situations like this the base usually can be setup to work, but the corrections connection between the base and rover (drone) can be unstable. We move to this kind of antenna mounted on a separate tripod to get extra range. I have been researching how to implement a repeater to solve this, but have not figured out how to do it with Emlid.

Can give a little more information on your setup? Are the RFD900s used for telemetry as well?

  1. We do a lot of work in thick veg too. Are you flying under the canopy or is this in reference to where you are forced to place the base?

  2. I don’t foresee a bandwidth issue by adding just the L2 on the RFD900. What are your settings currently and what kb/s are you seeing on those?

Sounds like you are trying for RTK but can you PPK? Be much easier. If can PPK set that base up in a better location and not worry about real-time corrections. You can go well beyond the range of the L1 for sure for corrections.

If need RTK and have cellular available throw those corrections to a caster and connect the M2 to cell modem

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We use the RFDs for incoming telemetry as well as outgoing RTCM3 corrections, RTH commands, etc.

  1. We are forced to place our landing zone in strategic locations for our surveys and that often is surrounded by pretty tall pine trees. Fix can be hard to get on ground level and hard to keep during flight because the base is still getting cycle slips. All flights are done above the canopy.
  2. I can’t share much about our radio settings right now as I don’t know them but I guess my question is how much more kb/s is needed to transfer L1/L2 as opposed to L1 only?

We used to work with PPK but we realized that RTK is necessary for our purposes.
As for cellphone services, it is pretty rare we have some or that it is of good enough quality. We also prefer to keep everything going and coming through the same system (telemetry).

Thanks for your help!

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Hi Michael,
We use 5db antennas like these.
We always have the base and rover near each other (20-30m) at takeoff so we have no problem transmitting corrections. Problems arise when we the drone is in flight and about 1.5 km away, the corrections have some trouble getting through the canopy indeed. Our base antenna is about 10 meters high and the rover at about 30 meters while in flight. We are also trying different antenna configurations.

All good points and we experience the same struggles. I too prefer to keep everything going through the same airwaves. How is the eprformance of the RFDs in those conditions? they drop out?

So back to 1. the M2 would help acquire fix. Can you power just the GNSS without powering on rest of system to save battery while getting fix too? This is how I am setting up next copter.

  1. I think be simple test to quantify if someone has both the M1 and M2. I would but no M2 yet in possession.

Can describe your workflow and why RTK necessary?

I think you would benefit from a taller, more powerful 8-12dbi antenna, but how are you getting 10m on the base? By rover I meant drone and this is why I won’t run RTK on the drone. Even with our Topcon equipment the radio connection to the base is what makes use lose fix. If you are in tall trees then the base losing LOS to the drone because the drone is so low then flying higher may help as well. This is all said with your L1 receiver in mind and you may not have any of these problems with multi-path…

The RFD holds steady for incoming telemetry but we experience long dropouts of RTCM3 (sometimes over 60 seconds without corrections) in the outgoing signal once we get a about 1 - 1.5km away from the radio. Our guess is that RTCM3 messages are easily disrupted by the canopy, more than the incoming telemetry.

Yes we power the M+ independently so it can keep receiving corrections while the system is turned off.

Good to have a confirmation that L2 will help the fix acquisition! We’ll look into the correction transmission if we can get our hands on a unit. Will let you know what we find.

RTK is necessary for us in order to make sure the drone is always flying at the same altitude, relative to the DEM. Traditional GPS proved to induce to much error, we had some variations of over 5 meters in our altitude.

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RTK shouldn’t be required for positioning when mapping unless you are trying to fly less than 10m from the subject. Sounds like something else is wrong if you’re getting 5m change in altitude… What DEM are you using?

The base itself is about 1m from ground level but the antenna transmitting the corrections is jacked 10 meters high. We jack it this high because we want to keep LOS as much as possible between drone and antenna. We will try different more powerful antennas, but heavier antennas might mean we can’t pull them as high as the other ones.

Wow makes sense know, 10m is way up there. What size of maps are you trying to fly in one position? Does your area not require VLOS?

I have been doing quite a lot of work in heavily canopied environments, from East coast to the West coast of the US. I have used all of emlid’s products from OG RTK to the new M2 and RS2. The RS2 and M2 are much better than the original products but when operating in degraded environments such as thick canopy we still need to be realistic in our expectations of the GPS units obtaining and maintaining a fix, its just not realistic to think you will. Another important factor is to plan your data acquisitions that coincide with good satellite coverage, there are plenty of sites to look at, that will help you determine the best or optimal time to do so. I will mention that my RS2 on the recent project in very thick canopy in Florida were hit and miss sometimes you had a fix but more often than not it was a float, but again we had no choice but to setup the base in a not great area due to multiple constraints. The RS2 and M2 are not some new magical GPS unit that will work in environments where others won’t, folks need to be realistic in their expectations when using them in these areas, they also should consider doing PPK if you really need the absolute accuracy!!! I am running my M2 on a RFD900x as well, have seen no bandwidth issues when using an air rate of 64kbs.


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