950 nm, 1.3um and 1.5um are problem wavelengths for atmospheric transmission. No need to use a telescope-you don't need that degree of precision and/or grade A optics to gather light and focus it on a photodiode. You get more band for the buck with a 10 inch fresnel, or even a 4 or 5 inch surplus glass lens. With a decent receiver and a small array of LED's for a transmitter, you can do a mile with a carrier or PWM transmitter...or up to 5 miles if you use baseband. Regards, Art At 11:27 PM 3/13/04, you wrote: >On Sat, 13 Mar 2004 15:44:10 GMT, Dave Dilatush >wrote: > >>Andrea wrote... >>> For the receiver I'm thinking about using a small telescope, pointing >>> it to the transmitter (hopefully 1+ Km away.. ehm). Will the lens be >>> transparent for the incoming 875nM or 950nM light? > >Surely at that sort of range you would be better going with an RF solution >no? At those sort of distances atmospheric scattering, dust, fog & heat >lens effects will be tremendously problematic. If you are really >determined you would be much better going with a powerful IR laser such as >one salvaged from a CD burner (808nm i think), but be careful of your >eyes, only work on it using a video camera so you can see what you are >doing. > >Regards > >Alex Rice > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics