Testing signal strength at a new racing track is something I do religiously after one close call cost me a quad in 2019. The process starts before you even power up. Walk the entire track perimeter and look for obvious sources of RF interference like high-voltage power lines, cell towers, WiFi-heavy buildings, or metal structures that can bounce signals around unpredictably.
Once you've scoped the location, power up your quad and radio. Set your RSSI warning thresholds in Betaflight or your flight controller software. I typically set my first warning at 50 RSSI and critical at 35, though these numbers vary depending on your system. For Crossfire, I use 70 for warning and 50 for critical since it reports differently than FrSky or other protocols.
The actual range test requires a spotter. With the quad on the ground and armed without props, walk backward from your starting position while watching your goggles or ground station. Keep your transmitter aimed at the quad in your normal flying orientation. Every 25 meters or so, note the RSSI value. I record these on my phone: 100 at 0m, 92 at 25m, 85 at 50m, and so on. Pay special attention when moving behind obstacles like trees, buildings, or terrain features that might block line of sight.
What you're looking for are sudden drops. A gradual decline from 100 to 60 over 200 meters is normal and predictable. A drop from 95 to 45 when you step behind a concrete wall tells you that's a danger zone during racing. I once found a spot at an urban track where RSSI plummeted near a particular building corner, turned out there was a commercial radio repeater inside creating havoc on 2.4GHz.
Test multiple paths around the track, not just one direction. RF propagation is weird and directional. I've seen tracks where signal is solid flying clockwise but drops when going counterclockwise because of how the transmitter antenna orientation interacts with the environment.
Also test at different heights if your track has elevation changes. Put the quad on a chair or ladder to simulate altitude. Ground-level testing won't reveal problems that occur when flying 15 meters up near metal roof structures.
Document everything. Take photos of problem areas and mark them on a track map. Before your first hot lap, do one slow reconnaissance flight at half throttle, constantly monitoring RSSI. If you see values approaching your warning threshold anywhere on the course, that's your no-fly zone or the boundary where you need to adjust your racing lines.
