In this tutorial, a terrain profile will be generated from USGS 30 second elevation files copied to your computer during the TAP installation process.  The data files for the area in this example are correctly installed and indexed during the setup process.  Other articles contain details for adding and indexing other data files to your system.  That information will be useful if you add more topographic data files to your TAP system to cover other geographic areas.

From the main menu of TAP, use your left mouse button to click on the Path menu, then on the Path Profile option to display the TAP Point to Point Study screen pictured below.

Your screen may or may not display previously entered site descriptions in the Site Specifications frame depending on whether you have run any of the Path programs prior to this time. You will enter data in the point to point tab folders in order to configure your path profile.

As you can see, the default coordinates for Site A and B are identical. This is a pretty short path! Let’s edit Sites A and B in order to define our path. At this point, you have several options. If you press the Fixed Facility Lookup button, you will access the facility lookup screen where you can view, edit and even create new fixed facility data base records for use with this and other TAP programs (see the Fixed Facility Data Base tutorial for more information). When you close the lookup screen, site parameters stored in the current data base record will appear here in the Site tab. In the same manner, you can access coordinates from the TAP Location Data Base and write them to the Site A and/or Site B parameters fields. Recording site parameters in the facility and location data bases allows you to site information from a centralized data base thereby reducing your data entry time. In this tutorial, we will simply enter the parameters directly into the site fields displayed on this screen.

Position your cursor to the Description field in the Site A frame on the left side of the sites tab. Edit site A in the following manner so that it looks like the screen pictured below:

• Type "TX Path Profile" in the Description field
• Type a Latitude of 38 44 45.00 N and a Longitude of 104 51 39.00 W
• Click on the down arrow to the right of the Datum field and select "NAD 27" with your left mouse
• Click the "Interpolated" button for elevation mode. This will cause the program to get the site elevation from the topographic data base. In this case, TAP inserted 8714 ft into the elevation field. The "Specified" mode is used if you know the elevation of the site and want to use that value instead of the interpolated value.
• Enter a Center of Radiation of 300 above ground level (AGL)
• Make sure that your Center of Rad units list displays ft

Now edit site B in the following manner so that it displays the Site B parameters pictured below:

• Type "RX Path Profile" in the Description field
• Type a Latitude of 39 25 39.00 N and a Longitude of 104 52 00.00 W
• Click on the down arrow to the right of the Datum field and select "NAD 27" with your left mouse.
• Click the "Interpolated" button for elevation mode
• Enter a Center of Radiation of 100 above ground level (AGL).
• Make sure that your Center of Rad units displays ft.

As you can see, TAP calculates the Azimuth and Path Length in response to changes you make to the latitude and longitude fields. You also have the option to calculate Site B coordinates by first defining the Site A coordinates and then entering an azimuth and path length. In that case, the Site B Latitude and Longitude fields display the profile end point coordinates in response to changes made to Azimuth and/or Path.

The site descriptions and path information should look like ours below.

We define the characteristics of the terrain data extraction process in the Topo Data options folder. Click the Topo Data tab with your left mouse.

The Topo Data options will be displayed:

In this case, we instruct TAP to generate a profile in 0.1 mile steps using the FCC 4 point interpolation method for each point along the profile. Earth curvature determines the effective atmospheric diffraction for the path. A typical value of "4/3 earth" (1.333) appears by default.

Because we have only 30 second terrain data available for this tutorial, toggle off the 30-meter and 3-sec data options by clicking each check box with your left mouse.

Now click the Path Profile options tab folder.

The profile options will be displayed:

You have several plot options available for your terrain profile and associated line of sight/Fresnel zone:

• Show effective earth curvature by …: The Terrain Data option will bend the topographic data up and the Line of Sight option will bend line of sight and the Fresnel zone down
• Earth Curvature Reference lines: You can add lines on the profile plot to show the effect of earth curvature, drawing either "All" lines to add lines uniformly on the vertical axis of the plot, or "Base Only" which draws just one line at the bottom of the drawing.
• Fresnel Zone: Fresnel N is the Fresnel zone number to plot
• Fresnel Clearance Ratio: The Fresnel ratio is the portion of the Fresnel zone to draw. Half the first Fresnel zone (.5) is typically used for diffraction loss calculations. Any obstruction that penetrates half of the first Fresnel zone will generally introduce additional loss.

For this tutorial, verify that the option to show earth curvature by Terrain Data is selected with your left mouse. Verify that the "Base Only" is selected. Finally, check that N = 1 and the Ratio = 0.5.

Frequency is one of several variables used in the calculation of the Fresnel zone. Position your cursor to the Frequency (MHz) field and type in a tutorial frequency of 450.

The "Surface" tab (which is not discussed in this example) is used to add Surface Features (vegetation, building clutter, etc.) to the profile plot.

When your screen looks like the Point to Point Study screen pictured above, select Continue to draw the profile plot.

You will need to wait momentarily while terrain data is extracted and the profile is drawn. Many of the plot control buttons will be discussed in other tutorial sections. This tutorial will focus on options specific to the profile plot.

Summary information about the sites and the path between the sites appear at the top of the plot. The terrain profile appears in 0.1 mile steps along a distance of 47.02 miles. It is apparent that at least one peak along this path blocks straight line of sight completely. Another peak, which appears just beyond the 32 mile tick mark, appears to be just below the straight line of sight.

We can zoom in on this peak. Click the magnifying glass button

The program will prompt you to click two points to define a rectangle for the zoom area. Click with the left mouse button to draw a rectangle around the peak.

After we set the second point of the rectangle, the following plot appears.

Because Zoom also enlarges the drawing pixel sizes resulting in wide, jagged lines, we need to refresh the drawing. (The "R" button will probably turn red, indicating that a refresh is needed.)

Click the button with the "R" to refresh the drawing.

(You can also set the Auto-Refresh function using the Configuration button with the wrench icon. If this option is set, the drawing will be refreshed automatically.)

It is now apparent that this first peak penetrates the Fresnel zone but it does not block line of sight. As we discuss later, some degradation of signal is to be expected even though line of sight is not blocked.

Let’s zoom out to our starting point. Press the button with the "100%" label, then refresh with the R button once again.

The profile drawing is re-displayed:

Can we design a point to point system without line of sight problems? Select the Options button on the toolbar:

This will display the Options form for the profile plot.

The TAP Terrain Profile Plot Options tabs allow you to modify many characteristics of your plot including several options such as earth curvature and reference lines that we discussed previously.

• Axes: The options screen opens to the Axes options tab folder where you can modify tick marks and text for the distance (X axis) and elevation (Y axis) axes.
• Topo Data: Change the topographic data parameters such as your data interval in order to re-extract terrain data and re-display the profile plot
• Curvature: Modify earth curvature or add earth curvature reference lines to your plot
• Line of Sight: We will work with the line of sight/Fresnel options in this tutorial to add a new line of sight and Fresnel zone to the profile
• Surface: At your option, you may instruct TAP to determine if your path crosses through any surface feature objects such as a building or a grove of trees contained in one or more selected files. If your profile passes through an obstruction, TAP will graphically depict this surface feature object along the path and incorporate the specified height of the obstruction in its line of sight and Fresnel zone calculations.

A number of the functions on this screen are discussed in detail in other tutorials. For our purposes, click the "Line of Sight" tab.

As you can see, the line of sight and Fresnel parameters that are displayed correspond to the current line of sight and Fresnel zone on the plot, as indicated by the 300 ft Site A antenna center and the 100 ft Site B antenna center. The Mode displayed in the Site A and Site B frames refers to the option of using either a Specified site elevation ("MSL") or an Interpolated Site MSL calculated from the underlying terrain data base.

As mentioned, our goal is to design a system without line of sight blockage. What if we raise the antenna center of radiation on the receive end to 400 ft? Position your cursor to the Site MSL field in the Site B frame. It currently reads "100.0000". Change it to 400. Also, be sure the "Replace" option is selected. This will delete the current line of sight and Fresnel zone from the profile plot before adding the new information. The "Append" option keeps any current line of sight and Fresnel zone on the plot.

Click the Draw button on the TAP Terrain Profile Plot Options form:

Then click the Close button on the TAP Terrain Profile Plot Options form.

This will draw our new line of sight and Fresnel zone on the profile.

As you can see, we now have clear line of sight but one peak penetrates the Fresnel zone near the 36 mile mark. What effect will this potentially have on transmission between the two points? TAP provides a method of predicting an estimated knife-edge diffraction loss when there exists a penetration into one half of the first Fresnel zone. The first Fresnel zone is typically used for diffraction loss calculations.

Position the cursor over the peak. The estimated knife-edge loss from the peak is displayed at the bottom of the profile.

At 35.4 miles out, the path clearance is less than half of the Fresnel zone, resulting in an estimated loss of 4.24 dB. Note that loss is calculated for one half (Fresnel Ratio = 0.5) of the first Fresnel zone (N = 1) regardless of the N and Fresnel ratio specified when you instructed TAP to draw your line of sight.

This concludes the profile plot introduction. Note that we have demonstrated only a few of the plot options available with this program. You may wish, for example, to draw earth curvature reference lines or perhaps bend line of sight to reflect earth curvature instead of bending the terrain profile as we have done. What affect would a different frequency have on the Fresnel zone clearance for your path? You can experiment with the plot options contained in the index tab folders of the Terrain Profile Plot Options screen.

When you are ready to exit the profile plot program, select the Close button in the TAP Plot Controls screen to close the profile screens and return to the main menu.