MultiNav Pro+ BLE range test - line of sight vs Fresnel zone clearance?

@Joseph Hernandez yeah this is actually a really important distinction that trips people up — the 50km figure is drone-to-drone specifically because both ends are airborne and you've essentially eliminated ground reflections and multipath, which means you're getting close to true free-space path loss conditions. At 10-15km with 60-70% first Fresnel zone clearance you're going to see a measurable RSSI hit, probably in the 3-6 dB range depending on the geometry and what's causing the obstruction — that's not catastrophic but at longer ranges where you're already working closer to the sensitivity floor it can matter.

 

The receiver sensitivity on the module is doing a lot of heavy lifting here, but it's not magic — Fresnel zone obstruction adds diffraction loss on top of free-space path loss and no front-end can compensate for physics. The practical thing I'd suggest is try to get 80%+ clearance if you're pushing toward those longer ranges, and pay attention to whether your obstruction is a hard edge (like a ridgeline) versus distributed (like tree canopy) since the diffraction characteristics are quite different.

 

What's your deployment scenario — fixed ground stations or one end is a drone?

60-70% clearance will hurt you more than you'd think at those distances - Fresnel obstruction loss isn't linear and you'll start seeing meaningful RSSI degradation once you dip below that ~80% threshold, especially in the 10-15km range where the zone radius is already pretty wide. The RF front-end has solid sensitivity but it's not magic, it's still bound by the same physics, so I'd treat that 50km figure as needing basically perfect LOS with full zone clearance. If you're stuck with 60-70%, budget for maybe 20-30% range reduction and tune your link budget expectations accordingly.

Joseph's got it right, and I'll add that in my testing the 10-15km band is kinda where the Fresnel sensitivity really bites you because the zone radius is expanding fast relative to typical terrain clearance margins - I was seeing closer to 25-35% RSSI degradation with 65% clearance at 12km which pushed me right to the edge of reliable packet reception. Ended up having to bump tx power and accept the trade-off on battery side, so definitely factor that into your link budget before you're out in the field scratching your head.

Both Barbara and Joseph nailed it - I'll just say from my own field work that antenna height is your cheapest fix here, even getting a few extra meters of elevation at one end can recover a surprising chunk of that Fresnel clearance without touching tx power at all. At 12km you're looking at a zone radius somewhere around 8-9m depending on frequency, so small height gains actually move the needle. Definitely model it out in something like RadioMobile before you commit to a deployment config.