Hey everybody, we are currently working on a weather balloon project with a lot of sensors and hopefully a telemetry system. We already have the sx1267 lora module for sending the data from an ESP32-WROOM-32D. The data will also be stored on a SD card. Our trouble starts with the ground station. The original plan was to use a public lora gateway to send the data to but I am not very optimistic about the reliability of those in our vicinity. So our new plan is to build our own gateway or ground station but we have no idea what the hardware requirements are (so what kind of receiver and antenna do we need for a 50km line of sight range). Price is also something to consider. A quick look in the market of LoRa gateways shows some hefty price tags and we have to stay on a budget...
I hope somebody can help us :)
There are a number of tutorials on DIY LoRa gateways, some with very detailed construction advice. Spend some time on the web studying them. Example search phrase "arduino diy lora gateway".
No need for a 'gateway' a simple Arduino and LoRa module will do. This could just be an Arduino Pro mini (3.3V !) and a SPI LoRa module.
50km line of sight would only require a 1/4 wave length of wire for the transmitter and receiver.
I use The things Gateway (connects to Ethernet) and the Things Indoor gateway (connects to WiFi) - both fairly low cost
You might want to look at this Andreas Speiss video and its part 2 on LoraWan gateways:
Be aware that LoRaWAN\TTN transmissions from high altitude balloons can create a significant amount of traffic in the back end systems.
At high altitude the reception distance, balloon to ground could easily be 100km, the current record is 832km.
So for instance one high altitude balloon could be sending out signals that are received by most all gateways in Europe. Not sure LoRaWAN\TTN was designed for 'applications' like that.
Simple point to point LoRa will handle the comms just fine. I had two way comms from my workshop to a foil party balloon which was only at 10km altitude when the balloon was 242km away. And I was using Pro Minis for transmitter and receiver.
If your interested you can use the LoRa module to transmit FSK RTTY data which can then also be picked up at long distances, 500km or so. A lot of radio hams will have the SSB gear to decode FSK RTTY as well, or just use an SDR.
First of all thank you (all) for your quick response,
I just watched this video from the BroneBot Workshop and as I understand it from what you said the setup in Demo 1 should basically reach for around 50-100km in line of sight range. This kind of sounds incredible for this small of a setup 
.
Thanks a lot for your answer.
Is the orientation of the antennas important or should it just "dangle" out the floor of the balloon?
And do we need a dual antenna setup for the receiver on the ground or is a single wire actually fine?
Most balloons just use a simple bit of 1\4 wave wire that dangles down vertically below the payload. You can tape on 1\4 wave radials too. Balloons spin so any form of directional antenna is fairly pointless.
What is a 'dual antenna setup for the receiver' ?
I heard that usually you use two antennas with a 90 degree angle between them.
RCModelReviews explained it that way in this video from 19:00 on.
Just not true at all.
Do you think the antenna hanging below a balloon payload is suddenly going to turn from vertical to horizontal ?
true...
I think we are just gonna try to set it up as you described it with the 1/4 wavelength wire - is the thickness of the wire relevant an how precise does the length need to match the 8,63cm for 868MHz?
Thickess of wire not that significant.
Length within a couple of mm OK.
Its quite likley that the true optimum length is not exactly 1\4 wavelength in the first place. But trimming the length to get a dBm or two extra output is not that simple.
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