TAP6 Field Strength Recalculation

Q:  How can I run the same field strength study again if I only want to change one or two parameters?

A:  If you want to change parameters that do not change the geometry of the path (as explained below) you can use the Field Strength Recalculation function.

Note that all values in this example are for demonstration purposes only.  You should determine appropriate settings for your application.

(The illustrations in this article show the Field Strength Recalculation form as it was revised in TAP6.0.2210, and is available to TAP users with a Maintenance Subscription date of January 31, 2008, or later.  If you are using an earlier version of the software, please refer to the Field Strength Recalculation article, or update your software to build 2210 or later.) 

The recalculation function enables you to change power levels or directional antenna information from a previously run study. The results from the previous study are adjusted for the new parameters. For example, if you ran a study with an Effective Radiated Power (ERP) of 100Watts, then used the recalculation function to adjust the power to 200Watts, the computed field strength at each location would be adjusted for twice the power (+3dB).  The advantage is that the recalculated study is based on the previous results and does not need to retrieve the topographic elevation information for the path to every point that is computed.

Since the recalculation assumes all paths, antenna heights, Fresnel clearances, etc., will be unchanged, you cannot use that function if you want to change antenna heights, or use different topographic data, change frequencies, etc. In those cases, the study with the new parameters will have to be run from the normal Area Coverage function.

If you want to use the Field Strength Recalculation function, select it from the Area menu in TAP:

 

You will be prompted to select a TAP Coverage Study Task to open.  This is the Task that has already been computed and the one you want to use as the starting point for the Field Recalc function.  Select the Task you want to use and click the Continue button:

Note that only Tile or Radial studies can be used for the Field ReCalc function.  Only field strength propagation studies can be used.  Shadowing studies are not used with the Field ReCalc function.

The Field Strength Recalculation form is displayed.

 

Note several items on the form:

  1. The Task ID that you selected to use for the Field ReCalc function
  2. The Task Description for the Task you selected.
  3. A new Task ID for the recalculated results.
  4. A Task Description for the recalculated results.  You can edit this description, usually to indicate the changes made for the recalculation.
  5. The Auto Draw Map box is checked if you want to draw a map of the recalculated coverage when the Task is completed.
  6. The antenna pattern, gain, and mounding parameters that were used for the original Task.
  7. The Effective Radiated Power used for the original Task.
  8. The antenna parameters for the new Task.  You can change the mounting information (tilt and orientation), or you can use the Browse button (“…”) to select a different antenna for the recalculated Task.  If you select a new antenna with a different major Lobe gain, the ERP for the new Task will automatically be recalculated.
  9. The Effective Radiated Power to be used for the new Task.  This is a value that is recomputed if you change the new Task antenna gain by selecting a different antenna.  You can also manually enter a new ERP value here.

The information about the “Old” Task cannot be edited, but you can make changes to the antenna, mounting, and ERP values for the New Task.

For example, suppose you wanted to recompute the coverage with a different antenna orientation of 225 degrees.  Enter the new value.  When you click the mouse cursor out of the Orientation data box, the antenna preview will be updated:

 

When you are ready to run the recalculation, click the Save button on the toolbar near the top of the form:

 

Then click the Run button to start the study:

 

A list will be displayed of Tasks you may want to run.  Any Tasks saved during the current session of the Field Recalculation function will be checked.

Mark the check box for each Task you wish to run and click the Continue button.

The progress of the study will be displayed.  Note that the Field Recalculation study runs considerably faster than the original study.

 

When the study is completed, a shapefile will be created for mapping the study.

If the AutoDraw checkbox was marked, the new study will be displayed in HDMapper.

You can compare the results of the new study (with the major lobe of the antenna oriented to the southwest) and the original study (oriented to the northeast).

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