Xref: utzoo rec.ham-radio.packet:981 rec.ham-radio:4119 sci.electronics:2362
Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!glacier!jbn
From: jbn@glacier.STANFORD.EDU (John B. Nagle)
Newsgroups: rec.ham-radio.packet,rec.ham-radio,sci.electronics
Subject: Re: low power license free packet?
Message-ID: <17327@glacier.STANFORD.EDU>
Date: 28 Feb 88 00:20:24 GMT
References: <8802111609.AA16271@decwrl.dec.com> <440@n8emr.UUCP> <357@ge-rtp.GE.COM> <1170@trotter.usma.edu> <2005@ttidca.TTI.COM>
Reply-To: jbn@glacier.UUCP (John B. Nagle)
Organization: Stanford University
Lines: 23
Keywords: Bandwidth for nothing, gigabits for free


      Looking out the window at the overcast, a thought comes to me.  
Diffuse infrared systems have been built that work quite well indoors,
bouncing the signal off ceilings and walls so that line of sight is
not required.  Why not try diffuse infrared off the cloud deck as a
scheme for short-range outdoor communications?  Ranges of a few blocks
might be possible.  One could extend this with repeaters.  There would
be fading during good weather conditions, but in areas with smog and haze,
the atmosphere may never be transparent enough to prevent operation.

      Laser safety standards should not be a problem, since the beam is 
diffused very widely and the peak energy per unit area, the regulated quantity
for lasers, will thus be very low.  Detection will require heavy filtering,
both optical and electronic, but with narrow-band optical interference
filters, negative s/n ratio modulation techniques, and packet error
correction, communication should be possible.

      Incidentally, all the necessary optical components, including
interference filters, are available from Edmund Scientific.

      No FCC licence is required for "blinking light signals", of course.

					John Nagle