Since every situation is different, there is no "cookie cutter" approach. The following suggestions offer ideas of how the various TAP functions can be used in the process of designing your coverage system. Like any tool, the more you understand how the tool can be used, the better equipped you will be to adapt the tool to your particular circumstances.

(This article describes TAP functions for TAP5 and earlier.  For TAP6 and later versions, see the article for Area Coverage Studies with TAP.)

If the base station or repeater site location for the system is not already determined, several functions can help locate potential sites.

Once base station or repeater site has been determined for your system, several features available in TAP for the design and evaluation of the area coverage system.

Use the Shadow Study module (accessible in the Area Coverage function under the Coverage menu in TAP) to evaluate line of sight and Fresnel obstructions in the vicinity of a site. The shadow study can create a map showing areas that have line of sight from your base station (or from your remote station), as well as areas that have grazing or blocked paths.  You can add potential obstructions in the area (vegetation, ground clutter, buildings, etc.) using the Surface Feature editor.  These features will be included in determining the shadowing and line of sight locations in the shadow study, and can also be used in the path profiles and field strength studies described below.

Use the Area Coverage function to compute field strength values at numerous locations, based on the parameters of your base station.  Surface Feature files can be included in the coverage calculations using the advanced settings for a tile or radial coverage study. 

While the Shadow Study described above can give you general information on the line of sight and Fresnel zone clearance for a path to a target point, the actual value of the predicted field strength for different locations can be found from an area coverage study using one of the several propagation models available in TAP. This information will also be useful in selecting the best sites and the best paths for your point to point system.

You can also set up coverage studies from your remote locations to determine the field strength over the surrounding area. The areas of highest field strength would be a guide to the best base station to serve each of the remote locations.

Setting Up Area Coverage Studies

Coverage Area

TAP provides three ways to define the coverage area to be computed.

• Tile studies define an area and points within that area on a rectangular grid.
• Radial studies define a radius from a transmitter site and the radial directions out from that site.  Field strength values are computed on points along the radials.
• Contour studies use information from radial studies to define a single closed contour around the site representing a user-specified field strength level and percentage of coverage locations.

Basic and Advanced Studies

Basic studies are the easiest to set up and are useful for most typical coverage applications.  Basic studies have the following characteristics:

• All studies are centered on the specified transmitter site
• All Radial and Contour studies are based on uniformly spaced radials, such as every 1 degree, every 5 degrees, etc., for 360 degrees around the site.
• The assumed effective earth curvature for the studies is 4/3 earth (1.333)
• Basic studies always use the FCC Interpolation method for elevation values.
• No Surface Feature or Land Use information is included in the studies.

Advanced Tile and Radial studies offer more flexibility in defining the coverage area to be computed.

• Advanced Tile studies can be defined for a rectangular area not centered on the transmitter site.  For example, if the base station is on a remote mountain top and the area of interest is in a populated area several miles away, an advanced tile study can define just the area of interest and avoid unnecessary calculations in the vicinity of the remote site.
• Advanced Tile studies can also be defined for an arbitrarily shaped area (such as a county boundary).  This enables you to prepare a study that is customized to your area of interest.
• Advanced Radial studies can specify radials at any azimuths (not necessarily equally spaced) and of any lengths.  The radials can also be limited to a desired aperture and not necessarily for all 360 degrees around the site.  For example, if you have a base station on a mountain top and you are only interested in coverage to east where the target population is located, you can set up a study for azimuths from 45 to 135 only.
• Advance Radial studies can be used to compute field strength values at target points.  For example, suppose you have fifty telemetry locations around your base station.  You can specify the coordinates of each location and the program will compute the azimuth and distance for each location.  Then you can use the Radial Ends Only option to compute only the field strength at the locations, since the field strength along each radial is not important.
• Advanced coverage studies can include Surface Feature and/or Land Use information in the study.
• Advanced studies can be computed using a different value for effective earth curvature.
• Advanced studies can use one of the different interpolation methods for elevation values.

Speed vs. Detail

Radial studies have the advantage for speed.  Since all the computed points are on the radials, the topographic elevation data for each radial is used for every target point on the radial.  Tile studies define the target points on a grid, so the topographic data along the path from the transmitter to each point is unique.  More time is required for Tile studies to obtain the needed topographic data.

Tile studies have the advantage of a more uniform presentation of the coverage area, since the target points are on a uniform grid.  Radial studies have the "spokes of a wheel" look, so that the distance between radials increases as you get farther from the transmitter.

TAP gives you the flexibility to use whichever type of study is best for your circumstances.  For example, if you are comparing coverage from ten potential repeater locations, you can quickly set up and run ten radial studies in batch mode.  Basic radial studies, especially if you specify every five or even every ten degrees (72 or 36 radials) will run quickly, giving you an immediate comparison of the merits of each of the ten sites.  When you narrow the options down to the best three sites you may want to run a more detailed radial study or tile study for each site.  For the final site  you select, you can use a tile study for the best presentation of the results.

Contour Interpolation

Contour studies using Broadcast and Carey propagation models compute the distance to the desired contour along each radial.  Other propagation models (Longley-Rice, Bullington, Okumura, etc.) are designed to compute field strength at discrete points.  Contours based on these models use the computed values along radials from the transmitter and interpolate the desired contour value from those points.

Topographic Data

The Topographic Data item under the Configuration menu enables you to define where TAP should look for topographic elevation data for coverage studies, path profiles, and any other function using elevation values.  Normally, you only need to make changes to the configuration when you first install TAP, or when you add or remove data files, or if you need to move data files.  The Config button on the Area Coverage Setup form enables you to view or change the configuration if necessary.  (Note that the configuration function will depend on the version of TAP you are using.  TAP 4.0 - 4.4 use an older configuration system, and TAP 4.5 and later use the TopoScript data retrieval engine.)

By default, TAP uses all of the available data files it finds based on the Topo Data Configuration settings.  If you want to select only certain data of a certain resolution for a particular study, you can select only the data you want.

The topographic elevation data available to TAP can be in a variety of file formats and resolutions.  You can set the topographic data increment for the path from the transmitter to each target point (tile or radial).

Propagation Model

For Area Coverage studies, you can select any of the propagation models which are licensed to your TAP system.  The available models for your TAP system are shown in the pulldown list on the Area Coverage Setup form.

Each propagation model has its own set of parameters that determine how the model will compute the field strength values.  You can enter or edit these values with the Edit button in the Propagation Model section of the form.

Mobile Facility Database

You can define the type of mobile unit to be used for the coverage calculation from the Mobile Facility Database.

An important parameter for evaluating the coverage area is the Required Field value for each type of mobile unit and each scenario.  The Area Coverage study in TAP computes and saves the field strength value at each location.  By applying the appropriate Required Field value(s) at each location, we can determine what mobile units will have enough signal to operate and under what circumstances.  The Required Field calculations, the Required Field settings, and the loss values to be considered are important parts of the area coverage study.

The coverage study is computed based on the one mobile facility you select, but the required field values for other scenarios can be included on the coverage plot as described below. 

Boundary Files

The Area Coverage Setup form enables you to include boundary files to be included on the coverage plot.  (If you enter coordinates for the transmitter site in the U.S., and the "Auto" box is checked, the default boundary file for the state where the coordinates are located is added.)  You can add or remove boundary files later on the coverage plot as described below.

For Advanced studies (Tile, Radial, or Contour) you can add obstacles in the area that may affect your coverage. You can import or create a database of buildings, vegetation or other "clutter" to be considered in addition to the topographic data (using the Surface Feature File function under the Editors menu in TAP). Path profiles, shadow studies, field strength studies, etc., can use this "Surface Feature" information to determine line of site, etc., considering buildings, vegetation, or other obstacles in the area.  You can also add surface features directly on the profile using the mouse.  You can also use USGS Land Use Land Cover information to determine the location of potential obstructions on a profile of the path or a map of the area.