On the night of 13th December 2025 Clive G4FVP and myself conducted another optical (850nm Infra Red light) test between our home locations.
Distance is 19km but not optically clear path – mainly buildings/trees are in the way.
I was running my usual optical beacon as high as i can get it on my tilt over mast – approx. 10m above ground, the beacon is elevated about 7degrees to lift the 15deg beam width up slightly above the horizon. I beam straight into 40-50ft trees in that direction which does not help matters! Clive was at ground level in his back garden with his optical Rx setup on a tripod.
Initially no signals but after a little elevation, around 5-10deg, my signal appeared on his receiver 🙂
This was an improvement on the last attempt, we now had maybe 10dB/noise in carrier mode. I have added Q65-300A mode to my Tx but it was cold outside so we didn’t get that setup in time to try.
Here’s the path, Tx is on the right.
Clive’s setup looked like this:
He is using a Fresnel lens and a 4xBPW34 receive head like I do for my tests.
Received signal on SpectrumLab ~1Hz bins:
Clive’s view towards my direction is not great!! he is beaming towards sky between trees and houses and is in town so there’s a significant amount of light pollution, it’s amazing anything gets through at all!
Hopefully we can do another test this next week and try out Q65.
