What is the simplest 100km RF communication link there is?

I am looking for a technology for sending sporadic bytes over RF hundreds of kilometers away - assume line of sight. What should I look into to do that? What frequency? What modulation? Perhaps what encoding? I am looking for the simplest technology around - I don't mind repeating my commands until they are executed. I don't need duplex, just send commands to a distant receiver. I think the power would be limited by what is allowed by the regulations rather than what I can provide.

Application: balloon

Answers 2

  • LORA WILL do what you want in many cases - and MUCH more if you try hard enough.

    766 km from a balloon.

    LORA with proper configuration is about the longest range system per link budget that you can get. The balloon range record was 714 km (!!!) in July 2019 - see Here. That's beyond some theoretical calculations but your 100 km is well inside theoretical.

    30-07-2019 - After almost 2 years, the world record of 702 km (436 miles) has been broken. Not once but twice. For a long time this record which was set on 26th of August 2017, seemed nearly impossible to break, until the Servet IV mission was launched. On 13th of July 2019, the record was broken by 39 km, setting a new record distance of 741 km. Interestingly, this record only held for 5 hours as another new world record was set with an astonishing distance of 766 km (476 miles).


    This is from LoRa 2.4 GHz Communication Link and Range

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    For a range limts paper see here and a look at this google search should be rewarding.

    Adding a decent ground side antenna will help. It's all covered in this paper.

  • As done before I would go with Packet Radio over VHF. Two directional yagi antennas, two radios and two modems. would work like a charm if LOS. With only a watt or two of power and intermittent sending of required short data bursts the setup could be solar powered. Also make sure to find a channel which does not get much traffic.

    Please note that due to curvature of the earth you will have to have one of the antennas at aprox 785m above mean sea level if other one is at 0m. Not accounting for fresnel zone. which could be as wide as 250m at this range and frequency. 360deg / 40030km(earth circumference) = 0.009deg/km so Angle for 100km =0.9deg height for LOS = radiusEarth * (1 - cos (Angle of great circle)) = 785m

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