Truncating a Radial for a Portion over Water - from Main Screen

TRUNCATING

Section 73.333(d) of the Commission's rules and regulation requires that, under certain circumstances, the 3.1 to 16.0 km radial for FM or the 3.2 to 16.1 km radial for TV be cut or truncated at the point the radial first crosses into water. Then, only the portion of the radial from the start of the radial (3.1 or 3.2 km) to the point where radial hits water should be used in determining the height above average terrain along the radial. (Read the section because this does not apply if one follows the radial azimuth and finds US soil.)

In the event you need to truncate a radial, CONTOUR for Windows allows the user to select the radial and view each elevation point for the first instance of water. The user can then set the radial termination point there by truncating the radial. The steps in the process are as follows:

Steps to Radial Truncation:
  1. ) Run a study to get the database elevations along user selected evenly spaced azimuths
  2. ) Click the Tools, then click the "Truncate/delta h" check box. Use the slider to select which radial azimuth you wish to truncate.
  3. ) The elevations along the radial will appear in the list box and the profile graph will appear. Next, determine where the radial hits water, usually at a sudden drop to sea or lake-level. Highlight this spot by clicking the elevation listing with your mouse or by clicking the graph at the point of desired truncation.
  4. ) Click the Set button to cause the program to memorize the truncated elevation on the chosen radial.
  5. ) To truncate another radial, repeat the process #3-#6 above.
  6. ) Click the Check button to sequence through the truncated radials.
  7. ) Click View button or View Menu item to produce a distance to contour printout with the truncated radials.
Delta H Calculations:
After selecting a radial, CONTOUR will display the delta h of the terrain along the radial path. Then end point of the radial can be changed by clicking the "Delta h" button and inserting a new distance. For more on delta h calculations see "Delta h. "

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