[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
More information about the Laser
mailing list