18 Mar 2013

8.5km "over the horizon" on 481THz tonight

This evening I ventured further afield with the optical kit to see if I could copy my QRSS3 beacon signal in the village of Stow-cum-Quy which is 8.5km from home . This is non line-of-sight and nearly twice as far as my previous tests last week.

Path covered this evening NLOS
Success! After quite careful searching both horizontally and vertically, the signal was copied and recorded at around 14dB S/N (at best) pointing just above the horizon. After searching for a stronger signal, the sky became increasingly "murky" and I was unable to find the signal again, so I came back home.
1W LED TX in 100mm optics, SFH213 detector in 100mm optics
This range is about the practical limit: aiming is very difficult and I find it is hard to get back to the same direction/elevation if I move anything. I need a tripod that is far more stable with some sort of degrees marking (both horizontally and vertically) so that I can go back to the best settings with confidence. At the moment it is a bit "suck it and see" to find the best aim and nearly impossible to get back to those settings easily if the tripod gets knocked.

This was clear air scattering as there was hardly a cloud in the sky. I have still to try cloud-bounce with real low level clouds.

To see the signal play this recording through Spectran with it set to 572Hz in 0.34Hz bandwidth. QRSS3 signal will be clearly visible.

There is a chance that I may try a much longer 27km NLOS path before too long. Looking at the map, this should be a possibility but I may need another 6-10dB from a Phlatlight LED and a MUCH more stable tripod!

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