§  80.769   Shadow loss.

   Where the transmission path is obstructed the received signal must be
   adjusted to include shadow loss. Attenuation due to shadowing must be
   taken from § 80.769 Graph 1, as follows:

   (a) Inspect the map(s) to determine if a hill(s) obstructs an imaginary
   line of sight (dashed line on illustrative profiles of § 80.769 Graph 1
   from the average terrain elevation at the coast station antenna to the
   water level at the ship location. If average terrain elevation exceeds
   the actual ground elevation at the antenna site, the latter elevation
   must be used as the average terrain elevation.

   (b) If a hill appears to obstruct the radio path, plot the antenna site
   elevation, the obstruction elevation and the height of the ship station
   on rectangular coordinate paper using elevation above mean sea level as
   the vertical scale and distance in statute miles as the horizontal
   scale. Then draw a straight line between the antenna and the ship.

   (c) If a hill obstructs the imaginary line of sight, determine its
   height (H) above the imaginary line and its distance (D) from either
   the coast or ship station, whichever is nearer, as illustrated by
   examples "A" and "B" on Graph 1.

   (d) Read the shadow loss from this Graph 1 and subtract that loss from
   the computed received signal.

   (e) Where more than one hill obstructs the transmission path, determine
   the height and position of a single equivalent hill, as illustrated by
   example "C" on this graph. Read the shadow loss from this graph for the
   equivalent hill.
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