Broadcast and Carey Contours

Broadcast and Carey Contours

Q: How do I compute and plot broadcast and Carey contours?

A: Since the broadcast and Carey propagation models use Height Above Average Terrain (HAAT) for contour calculations, and because only certain contour percentage values are permitted, there are a few special considerations for these contours.

To configure the HAAT specifications for you application, use the TAP Configuration menu and select "HAAT Specifications":

The HAAT Specifications form will be displayed.

Select the HAAT Type you want to configure. (This selection enables you to have different HAAT parameters for different propagation models.)
Set the Start and Stop distances for the HAAT calculation, as well as the Step (increment) value to use for averaging.
If the your application requires a Directional HAAT calculation, enter the offset aperture. (DHAAT calculations typically use the actual radial under consideration, averaged with a radial on either side, such as +/- 15 degrees.) If you are not using DHAAT, enter zero.
Enter the azimuths used in your application for computing the HAAT of a site, with the values separated by commas.
Click the OK button to save the parameters.

To set up a TAP coverage study using broadcast, Carey, or one of the other HAAT models, use the Area Coverage option:

On the Area Coverage form, create a New study and set the Study Description and the Transmitter Facility information as with other coverage studies (described in other TAP documentation).

For the Coverage Area type, use the pulldown list to select "Contour"
Enter the number of radials for the contour.
Enter the percentage contour to compute. Typically for broadcast, Carey, etc., this must be a specific value available for the model. For example, for the f(50,10) contour, enter a value of 10%, for f(50,50) enter a value of 50%.
Since these models depend on HAAT calculations, the "Distance from Transmitter" and "Distance between points" values on this form will be ignored.
In the Topographic Data section, specify the type of data to be used. The data "Increment" value will be ignored.
In the Propagation Model section, select the propagation model you want to use. If the model has additional parameters to set you can use the Edit button to open the template for that model to inspect or edit the values.
To set the value of the contour you want to compute, you can use the Mobile Facility database. If the contour you want is already listed in the pulldown list, select that item. If the contour you want is not listed, use the "Lookup" button to open the Mobile Facility database and add a new record.

Since these propagation models typically are used to compute distances to a specific contour value, you can enter the value as shown. It is usually not necessary to use the "Required Field Lookup" function to compute the contour value.

When the settings have been entered on the Area Coverage Setup form, click the Start button to compute the contour.