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Testing cheap($60) RTK module

Feb 27, 2018
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Brisbane, Australia
Hi guys,

This is not related to drones directly as I am looking to improve accuracy for GPS for my phone app on my Android. The current 5m accuracy gives me a lot of headaches for processing 360 photos and placing them on Google Map. I am not really aiming to 1cm accuracy but having something close to 30cm will save me a lot of time for photo processing.

So I found this and ordered one unit(lite version) yesterday
Polaris GNSS

It is only $60 for their lite version and I am hoping to use it as a rover with NTRIP caster server(seems I can use a free service from au government). I will probably get their standard version(all the same as Lite but different antenna) of Alpha just to be able to run it with my own base.

Together rover(lite version)-base(standard version) cost about $200 which is just dirty cheap and I could not resist buying it and trying it. They do charge plan fee($60 per year or $190 for lifetime) and offer an additional service for fixed base IP service(basically redirect).

Also if it works for my project with 360 photos there are some ways to use these modules on drones(Pixhawk / ArduPilot) so I may try later somehow try it with drones. You can get their manual from https://www.polaris-gnss.com/Alpha_RTK_Receiver_User_Guide.pdf

I will add all details once I receive the first unit and set it up.
Very interesting, this will allow us to compare with other systems, including the Yuneec RTK when it comes out. I have mine to mount too.

I join, the more information we have the better :)
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I got the receiver a few days ago. I broke a slider on 2 position switch the first time I tried to switch it. Now I cannot switch between base and rover config and I do not even know what config it is currently set to. The receiver is going back to Polaris for replacing the switch.

I have bought it to try with government bases but I do not think I can get any correction from them. They are quite far away from me(probably more than 60-70 kms).

I think after my receiver is fixed I will just buy the second one and set it up properly.
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It is just a silly design and very limited space where the switch is located. After I broke it I found a thread on their forum where people warning to deal with that switch gently. I was trying to even before I saw that thread but my fat fingers are probably to big for that space.
BTW, the receiver is quite lightweight. And if you take its PCB out of its plastic box it will be a few times lighter. Definitely it would be good for mounting on a drone.
I have finally got everything and testing RTK now. It is not hard to setup once you go through their manual and some advices from their forum and from their support guy.

The only problem I am facing now is communicating between my rover and my base over 3g/4G network for corrections. The technology needs to use port forwarding but most 3G/4G providers are connecting customers to Internet through 3G/4G the way that won't allow port forwarding to work.

The good thing Polaris provides redirect service for $45 for 6 month that goes around port forwarding and it seems to work. I have got a few days to test it for free.

The bad thing you wont get RTK if you do not purchase licenses from Polaris and they cost $65 per receiver for year and something like $190 per receiver for lifetime license. Without licenses receivers only give you 1 meter accuracy which is great anyway.

This is how their redirect service has to be setup

Unfortunately it rains a lot in Brisbane right now so I can only get a DGPS fix on 12 satellites near my house. It is not enough for RTK fix to be reached. I am getting 70-90cm accuracy on the rover system.

My base shows even better results reaching 20-30cm accuracy at its best because it comes with a better L1/L2 mushroom style antenna while the rover is used with a small square antenna.

I am going to some open place this weekend and I will test it in full. I will also need one extra sim with some DATA plan to verify that it will work over mobile 3G/4G.

I am using GPS+ BeiDou constellations now.
GPS+ BeiDou combination offers 70 satellites in total while GPS+ GLONASS combination is only 55 in total.
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This is not drone related but I believe it can be used with drones.

After setting everything up(one as a base and one as a rover) I got the base and the rover working together. Not ideal and I have never seen Full RTK or even Float Rtk fix this way(only reached DGPS fix) but I could not test it in an open area due to weather and limited time.

What I have found though that it is cheaper for me to use government NTRIP casters. They are free and require only one receiver as a rover.

I was aiming to this solution from the beginning(that's why I bought only one Alpha from a start) but I could not test it first for many reasons. I could not find how to setup NTRIP Client properly on my Android phone to work with gov caster and I could not find correct mount points from it.

Then considering that the closest gov base was 110 km from me I thought it was not going to work anyway and went with purchasing a second kit with Alpha to make base-rover setup..

In fact after a bit of work with setting NTRIP CLient properly to connect to that gov NTRIP Caster it works even with the base located at such a great distance from me.

If my alpha rover receiver sees at least 15 satellites Full RTK can be achieved in seconds even from 110 km away base.

So technically if you have government or free NTRIP casters in the area you service one set of alpha for $60 can do a full rtk trick for you.

Extra $65 will give you a license to use it for a year and $190 is for a lifetime license.

Alpha itself is not a perfect built quality product.

At least be careful with switches on it and ports. Bluetooth is a bit stupid and can be a trouble to connect too. Manufacturer recommends power on and off your Alpha to fix it but the best way just go through different modes until you set it to Bluetooth again(three pushes of a button). Then it connects straight away and stays connected without any problems.

There may be some other problems further the way but they are not GNSS related, it is more like Android stupid features that you may not even run into. So it will all depend where and how you can use the system.

For example if you want your own base you will need Polaris Redirect service($45 for 6 months) or you will have troubles getting to the required port on the phone where your base is connected to through Mobile 3g/4G.

Most of these connections won't allow port forwarding and very few mobile internet providers will offer you a fixed public IP to overcome this problem. So Polaris redirect service will solve that problem for you.

As for accuracy, I have seen 20cm and even 2cm with full RTK from that government NTRIP caster.

To be honest for my current application(slightly drone related) with 360 degree photography for GSV I am happy even with 70cm.

And 70cm you are most likely to get from one receiver even without using any NTRIP Caster . However to get under 1m of accuracy I believe you will still need to buy a license from Polaris. Otherwise it will be more like 2-5 meters.
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Interesting review, thx.

I imagine that the best solution will depend on where you live and if you have available a correct and sufficient network of GNSS stations. In my country, there is a public network of stations that allow you to have a connection less than 30km from any point to a station. You only need the connection to correct the fixed point of the RTK base. Once established this point, the communication of the base with the rober RTK can be donedirectly, for example through the telemetry of the dron itself.

More and more options are available. Thank you very much @Wingman , it is a very interesting topic :)

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