[Laser] daylight optical contact

Stuart stuart.wisher at talktalk.net
Thu Nov 17 06:47:07 EST 2011


Steve,


nice to hear from you and your daylight optical contact. Our small group of enthusiasts 
in NE England have been out in the daytime also. To date the furthest contact we have
made is 46km using Golden Dragon 3W LEDs as both transmitters, and reverse biassed 
as receivers. I used no filters at my end, and Brian, G8KPD used a red gel filter over his 
Fresnel lens (we both use single A4 Fresnel lenses in our transceivers). 


We also have been using 850nm IR LEDs to make daytime contacts, using 850nm long 
pass optical filters at both ends, again using the same LED on both receive and transmit, 
and have covered the same 46km path. On this contact I even placed an attenuator 
(an iris plate) over the lens and carried on the contact with 6dB attenuation (reduces the 
aperture by a factor of 4), and heard Brian using 12dB attenuation also. The last test 
used an effective lens aperture of just 5cm by 7cm. These demonstrate that the distance 
could probably be increased in the right weather conditions, to over the 100km mark, about 
the longest practicable path that is convenient in the UK.


Finally, we have made an initial contact on 940nm using LED transceivers, this time the 
distance was only just over 6km, but in full sunlight.


All these contacts were using sub-carriers on around 20kHz, on FM and SSB modes. 
We have transverters that enable the use of small HF rigs such as the FT817 to be used 
as the IF.


So we can safely say optical communication has come out of the dark, and into the light 
of day.


Regards,


Stuart, G8CYW
 


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