Sec. 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 Sec. 80.769 Graph 1, as follows:
    (a) Inspect the map(s) to determine if a hill(s) obstructs an 
imaginary line of

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sight (dashed line on illustrative profiles of Sec. 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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