Using SDR and computer to send data over internet

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Using SDR and computer to send data over internet

Post by rty » Sun May 26, 2019 10:52 pm

Hello, I'm new to radio communications, and I apologize for my lack of understanding. I use a high-accuracy RTK GPS system for auto guidance on agricultural equipment. This system uses a minimum of 2 GPS receivers - 1 stationary as a base station, and one rover on each vehicle using the guidance (multiple vehicles can use the system at the same time). All receivers have 900mhz radios on them so they can send GPS corrections to each other. As long as the receivers are within about 12 miles of each other, full accuracy is maintained.
The issue I have is that the 900mhz radios only give me a fraction of the system's 12 mile accuracy range. Rolling terrain and trees block the 900mhz signal once I get only a couple miles away from the base station. The radios would work great if they were always in line of sight with each other, but that's not very practical.
Here's what I would like to do:
1. Receive the 900mhz base station signal with a nearby internet-connected laptop and SDR
2. Send the data over the internet to another internet-connected laptop with second SDR in the vehicle cab
3. Transmit the data at 900mhz to the vehicle receiver using the second SDR, just as the base station would if the vehicle was in radio range with the base station.

I don't need to manipulate the 900mhz signal. I just want a pass-through pipeline of data over the internet, so the exact same signal being broadcast from the base station is broadcast from the SDR in the vehicle cab to the rover receiver.

Seems like this could be achieved somehow with SDRs, but I don't really even know how to get started. I would appreciate any input on if this is possible, and if so, what is the best way to do it economically. Thanks!

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Re: Using SDR and computer to send data over internet

Post by hotpaw2 » Tue May 28, 2019 1:06 pm

Whether possible depends on the protocol used by the 900 MHz radios (e.g. any message response latency requirements, etc.). If possible, it would require some full duplex SDR radios, such as the Hack RF, LimeSDR, Ettus Research, and etc. which are more expensive than RTL-SDR plug-ins.

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Re: Using SDR and computer to send data over internet

Post by rtlsdrblog » Wed May 29, 2019 4:43 am

It would probably be possible to pipe the raw IQ using rtl_sdr or rtl_tcp over the internet. You'd have to find a way to transmit that IQ data with something like a HackRF though.

The question is though, is the latency from the network going to be an issue? You'd likely be a few seconds behind on the retransmit which could cause issues with the GPS corrections as I would think that they're time sensitive.

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Re: Using SDR and computer to send data over internet

Post by Flexme » Mon Jun 03, 2019 11:09 pm

Which RTK setup the Trimble???

These use the ISM 902-928Mhz band. in the US.

How is the "BASE UNIT" mounted.

To achieve 12Miles on 900Mhz is most certainly possible, BUT NOT FROM THE unit mounted on the tripod in a field or something.

To achieve that 12M operation. It will need to be mounted ABOVE THE GROUND CLUTTER of the area, trees, buildings.

I would suggest that you look into improving the location of the base, ie: higher mount on a tower for one.

Other options are things like repeaters, that Trimble offers.

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Starting at page 58.

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