Building a RTK base station and reciever/modem with UHF

[bartdereu]

Hi all,

I'm trying to find a solution for my problem :
I have a Topcon AGI4 reciever with build in RTK radio , it's unlocked.
But it can only recieve data on 2G and 3G networks, who are ending their service this september in our country (not 2G, but it doesn't work that good)
So i thought i'd get rid of the cellular data and use an external modem to recieve the correction data over radio.

Since most of my fields are around the farm , in a radius of 2-3 miles , i thought this might be a solution.

So i'm looking for information on how to build it own my own. I did find a nice article on how to setup a base station with a raspberry pi,
https://learn.sparkfun.com/tutorials/how-to-build-a-diy-gnss-reference-station/all
but no real info on how to build a reciever/modem that sends to RTCM data over serial to the Topcon reciever.

any help is appreciated !

 

[Northern farmer]

You already have a Satel radio within the AGI-4 receiver. Why not purchase a compatible radio. Just need to check that both work on the same frequency, these are different even within Europe.

SATEL Satelline 2ASxm2 UHF radio-modem | eBay

Se envia manual - guía del usuario. Includes user guide. Estado impecable. Faultless, as new.

www.ebay.de

By the way, we have a Valtra with the same AGI-4 internal modem and it has been working on 2G for a long time already even if our 3G was shut down just recently. I guess your 2G network coverage is not as good as ours.

AGI-4 works very nicely with the internal radio. It is so clumsy with the cellular modem, not because of the Motorola modem but the way Topcon switches between the two and how they use the GPRS modem.

 

[bartdereu]

You already have a Satel radio within the AGI-4 receiver. Why not purchase a compatible radio. Just need to check that both work on the same frequency, these are different even within Europe.

SATEL Satelline 2ASxm2 UHF radio-modem | eBay

Se envia manual - guía del usuario. Includes user guide. Estado impecable. Faultless, as new.

www.ebay.de

By the way, we have a Valtra with the same AGI-4 internal modem and it has been working on 2G for a long time already even if our 3G was shut down just recently. I guess your 2G network coverage is not as good as ours.

AGI-4 works very nicely with the internal radio. It is so clumsy with the cellular modem, not because of the Motorola modem but the way Topcon switches between the two and how they use the GPRS modem.

So basically the radio is already present? and it uses the same antenna? I didn't know that. So basically i should just need a base station and connect to it trough UHF? I have to look into that on
how to do it in the Fendt, didn't really see an option to do so at first glance.

 

[Northern farmer]

Ideally the whip antenna should be replaced with another one. Both antennas usually come with the tractor, for some reason we only got two with the Valtra, not with the Fendt. I did some testing with our Fendt and the radio worked really well even with the GPRS antenna even if it is intended for 900/1800 MHz.

From the correction signal settings you should find the radio option instead of NTRIP. After that you can set the centre frequency to match the base.

 

[bartdereu]

Ideally the whip antenna should be replaced with another one. Both antennas usually come with the tractor, for some reason we only got two with the Valtra, not with the Fendt. I did some testing with our Fendt and the radio worked really well even with the GPRS antenna even if it is intended for 900/1800 MHz.

From the correction signal settings you should find the radio option instead of NTRIP. After that you can set the centre frequency to match the base.

Well i've learned allot. It seems that , since i bought my radio module in the UK and i live in Belgium, its range is from 450-459mhz. I can't use that frequency here so i'm stuck with an external
modem. I think i'm going to test first with a 'normal' telemetry radio on 915mhz and see if i can make that work.

 

[Northern farmer]

Which frequencies are allowed in Belgium? We could swap our 430 MHz-434 MHz radio.

Perhaps you could do like I did, we had a French modem on our previous Fendt (not officially allowed here) and nobody knocked on my door when I used it without any licence. Was running it at reduced power but your neighbourhood must be much more densely populated, nobody to disturb at our neighbourhood.

Hopefully the 915 MHz radio provides sufficient range for you.

 

[bartdereu]

430 to 434 is also allowed here.

Well , to tell you a funny story : i once bought a 'cell phone booster' on aliexpress. Because we had very terrible cell phone reception inside.
Ofcourse the damn thing didn't work like it should. i left it plugged in on my attick and forgot about it, until years later , 2 guys with a huge portable
antenna showed up at my front door saying they noticed a distortion miles away from here, and it led them to my house. Obviously i had my sender
and reciever antenna too close to each other, producing the distortion (just like when you hold a mic to close to the speaker)

So, i got a lecture but thankfully no fine .

Since then i'm a bit scared of messing with illegal frequencies haha But the area here isn't really that dense, but still.

What you mean by swapping radios? You need one that is the range of 450-459 and have one that works in 430-434
?

 

[Northern farmer]

430-434 is the correct frequency range for us but we have 100% 2G coverage supposed to be refarmed only at the end of 2029. I have no need for the radio, any frequency is fine. Even high power radio is not sufficient to cover all our fields (EDITED: a small farm but scattered fields), I would move to an external cellular modem (connected to the AGI-4 external modem port) if needed at some point or upgrade the whole receiver to a modern one (expensive on a Valtra as it needs a new screen too unlike a Fendt).

Odd that these AGI-4 plug-in modems are not easily available as a second hand product.

 

[bartdereu]

I think i'll make it easier on myself and go for a set of these :

RFDesign - RFD 868x-EU Radio Modem (UK and Europe) - Bundle

Choose a FC Cable separately, we recommend powering the RFD on your drone separately and not from the Telemetry port. The FRD radio modems require 5-6v and up to 800mA. Also available are the Aero Link adapter boards and bases. Includes 2 x RFD868x-EU Radio Modems 1 x Antenna, 868-900MHz...

www.3dxr.co.uk

 

[George Mitchell]

You already have a Satel radio within the AGI-4 receiver. Why not purchase a compatible radio. Just need to check that both work on the same frequency

So I'm sort of in the same boat as OP, having issues with ntrip not working well while giving it a go before trying to build my own base station, mostly incorrectly authorization errors (on 3 different casters on rtk2go, so think it is gsm related, using an O2 sim rather than m2m to give it a try).
Thing is, its not worth it for my use to go for subscription correction signal or a proper m2m sim on contract along with building a base on rtk2go, and the farm is all within a 2 mile radius, yard basically central so radio seems to be a better option.
Tractor has a trimble ag-382 receiver with an ag-715 450mhz radio in it, so how do you go about using the likes of this satel radio as a base?

 

[Northern farmer]

So I'm sort of in the same boat as OP, having issues with ntrip not working well while giving it a go before trying to build my own base station, mostly incorrectly authorization errors (on 3 different casters on rtk2go, so think it is gsm related, using an O2 sim rather than m2m to give it a try).
Thing is, its not worth it for my use to go for subscription correction signal or a proper m2m sim on contract along with building a base on rtk2go, and the farm is all within a 2 mile radius, yard basically central so radio seems to be a better option.
Tractor has a trimble ag-382 receiver with an ag-715 450mhz radio in it, so how do you go about using the likes of this satel radio as a base?

I'm afraid it is more complicated with a Trimble GNSS receiver compared to Topcon AGI-4 or Novatel. I'm not familiar with Trimble but there are Trimble experts on the forum and the Trimble radio topic has been covered on some other threads if you just can find those.

 

[George Mitchell]

I'm afraid it is more complicated with a Trimble GNSS receiver compared to Topcon AGI-4 or Novatel. I'm not familiar with Trimble but there are Trimble experts on the forum and the Trimble radio topic has been covered on some other threads if you just can find those.

Figured it would be, trimble gets that reputation for being awkward
There is another thread with basically the same thing,

AG-382 RTK Trimble conectar a una Base Topcon MR-2

How to configure RTK on Massey Ferguson Trimble AG-382 8737 Dyna VT, to connect to a TOPCON RTK base Topcon MR-2 Base with SRL-35 External Radio Frequency range: 410 to 470 MHz Protocol: SATEL 3AS PDL GMSK PDL 4FSK TrimTalk (P)...

thefarmingforum.co.uk

and the tractor end of it seems to be simple enough, had a play around with it before posting and it seems it is just as simple as changing settings to base station, however my query was more to do with how you get the radio to function as a base. Surely it would have to be broadcasting a precise location to be a reference point

 

[Northern farmer]

... however my query was more to do with how you get the radio to function as a base. Surely it would have to be broadcasting a precise location to be a reference point

Not sure what you mean with "the radio functioning as a base". You need a GNSS receiver in any case as a base, the GNSS base produces the correction data and this data is transferred to the rover (tractor) either via cellular data or via a radio modem. The accurate position of the GNSS receiver at the base is carried by one specific message but there are many other essential messages.

 

[George Mitchell]

That's what I figured, more to it than the "just buy a satel radio" that has been mentioned here and there

 

[Northern farmer]

That's what I figured, more to it than the "just buy a satel radio" that has been mentioned here and there

It should be obvious that a GNSS base station needs a GNSS receiver independent of the RTK correction data transfer method.

I believe the "just buy a Satel radio" refers to the scenario here where the tractor already has the radio (integrated to the GNSS receiver) and the owner already has a GNSS base station running NTRIP.

 

[George Mitchell]

Yeah, I think a certain amount of the confusion was regarding what a satel radio actually did, whether a dumb uhf radio transmitter or something more clever than that, but not quite the same as a gnss receiver. Dumb radio it is. Also that the OP in this thread doesn't have a base station, but in the other thread does.
Anyway have eyes on a receiver and radio setup at reasonable cost, just not sure if the uhf radio in the trimble works, and no way to try it before getting a base

 

[Northern farmer]

Yeah, I think a certain amount of the confusion was regarding what a satel radio actually did, whether a dumb uhf radio transmitter or something more clever than that, but not quite the same as a gnss receiver. Dumb radio it is. Also that the OP in this thread doesn't have a base station, but in the other thread does.
Anyway have eyes on a receiver and radio setup at reasonable cost, just not sure if the uhf radio in the trimble works, and no way to try it before getting a base

Doesn't make a difference here but it is not a dumb radio. It can do data buffering, data scrambling (whitening), forward error correction, programmable frequency, bandwidth and radio modulation type and baud rate etc.

 

[George Mitchell]

Doesn't make a difference here but it is not a dumb radio. It can do data buffering, data scrambling (whitening), forward error correction, programmable frequency, bandwidth and radio modulation type and baud rate etc.

Hence the confusion, theres a reason why they are expensive, but like you said doesn't make any difference here; for this application they are just transmitters
The programmable frequency is probably the only useful feature to match whatever receiver you have

 

[bartdereu]

I'm planning of making my build fully documented , so others can have benefit from it later on. As far as the trimble i know you can connect external modems to it , so i'm not sure how much more difficult it would be?
The biggest concern here is still transmit power of the radio , as i'm dealing with lots of trees here.

 

[bartdereu]

Small update. I've been doing quite some research today and came up with this :
My problem also is a bad cellular connection, i have the idea that the cell phone modem is'nt the greatest here. As said, 3G fades out in a couple of weeks
and the 2G connection is poor.
Where i live here in Belgium, we have a country wide free RTK correction signal called Flepos. It does a good job.

So what i'm going to try before i build my own station :
Just order a bluetooth module :

SparkFun BlueSMiRF v2 - WRL-24113 - SparkFun Electronics

The SparkFun BlueSMiRF v2 uses Bluetooth® to transform your serial connection into a wireless link.

www.sparkfun.com

and install the app called SW Maps on my phone

SW Maps - GIS & Data Collector - Apps op Google Play

Een compleet en eenvoudig te gebruiken veld GIS en mobile mapping-oplossing

play.google.com

‎SW Maps

‎SW Maps is a free GIS and mobile mapping app for collecting, presenting and sharing geographic information. Whether you are conducting a full scale GNSS survey with high precision instruments, need to collect large amount of location based data using nothing but your phone, or just need to...

apps.apple.com

The bluetooth module should be very easy to connect , only RX and TX to test it out (and power over USB for now)

In the SW Maps app you can connect to this bluetooth module and send out the NTRIP data from the connected server.

Should work, but it needs to be tested. Then i don't need a SIM card in my reciever anymore, i'll just use the 4G/5G signal
from my phone . IF it works, it's a pretty darn cheap fix.