Full disclosure; our current communications testing for the 2020 Medical Rescue UAV Challenge isn’t the richest material for a visual update!
We think that communications is the biggest challenge for the 2020 mission. We will need to maintain video, command and telemetry links with a QuadCopter in a farm shed 12km from our ground station. We will need to use a communications relay aircraft near the shed so that we can maintain radio ‘line of sight’ links throughout the mission. Its no small challenge to do this with lightweight accessible hardware! We are working hard on testing a number of communications options including 433MHz, 900MHz and 2.4GHz options.
We tested our current systems at 11.2km between a local hill and our flying site. With basic omni-directional antenna the RFD900Xs easily achieved and maintained a link with a 125kb air data rate. You can see below that this was a good enough to issue commands to one of our HolyBro Quads.
We have plenty of experiments left to do; we need to get some of the patch antennas set up so that we can do some experiments with our Airborne Innovations and MicroHard radios to see what performance we get from them at similar ranges.
Finally, we have another exciting option that we are working on. Carlos has been looking into some open source 433MHz digital IP based radios. These radios are called NPR (New Packet Radio). They are a custom radio protocol, designed to transport bidirectional IP traffic over 430MHz radio links (ham radio). This protocol is optimized for “point to multipoint” topology, with the help of managed-TDMA. Bitrate is advertised as up to 500kbps (net, effective bitrate). We’ll be experimenting with these soon and we’ll let you know how we go!