Modulated Light

by Mike Groth VK7MJ and Chris Long.

On the
evening of 19 February 2005 the authors spanned a 167 km
(104 mile) path between Mount Barrow's South peak and Mount Wellington
in Tasmania with
audio modulated light beams. This was the culmination of about 35 years
of
intermittent experiments by the two authors
of this web page, initially individually and later in association. The
suggestion to try the Barrow-Wellington path originated in
a chance comment to Chris Long by Jason Reilly VK7ZJA, that
Mount Wellington was visible from the top of Barrow. Jason is a
technician for Optus, regularly visiting the transmitter site on Mount
Barrow,
otherwise we would never have known that crucial piece of information!
Both
summits are above the 1200 metre contour, and the earth's curvature on
the land
between only accounts for approximately a 600 metre bulge, with
reasonable
clearance all along the path. We were surprised to find that the
expected rapid optical
fading cycles caused by atmospheric turbulence over this long path were
not too
severe,
presumably because the effect rapidly diminishes with elevation.