Once you have built a path using the " Process" command button and established the frequency of the radio path, you can adjust the transmitting height, receiving height, earth curvature and Fresnel zone to maximize your receiver's signal.
This can be changed from the "Xmtr Ht Mtrs" input box by clicking in the box with the mouse and then by typing in a new height. If the letter "F" is appended at the end of the height PLOTPATH will consider the input to be in feet and automatically convert the entry to meters. The user can also change the transmitting antenna height by simply clicking on the graph along the vertical line at the transmitting antenna location.
The receiving antenna height can be changed from the "Rcrv Ht Mtrs" input box by clicking in the box with the mouse and then by typing in a new height. If the letter "F" is appended at the end of the receiving antenna height PLOTPATH will consider the input to be in feet and automatically convert the entry to meters. The user can also change the receiving antenna height by simply clicking on the graph along the vertical line at the receiving end of the graph.
Use the radio buttons to select whether the transmitting and receiving antenna heights are in meters above ground or above mean sea level.
Note: As a good practice we recommend using AMSL height when the base elevation is available from a source that is independent from the terrain elevation database in use (Such as a 1:24,000 topo map.) This is because the resolution of the terrain elevation database may be such that the program has to interpolate between elevation points at the transmitter or receiver. It is possible that if the transmitter or receiver sits on a peak that the peak will not be represented in the digital terrain elevation database. Therefore, it is always better to use the exact antenna height above sea level when it is available.
From the "View" menu select "Path Elevation Values." This will open an edit window that contains the elevations in meters along the path from the transmitter to the receiver. First select the desired datapoint to edit. (Here we have selected the elevation at the 2 kilometer point.) You can insert any desired elevation value to replace the value the program draws from the terrain elevation database. This feature can be used when there are known obstructions in the path such as buildings or trees.
PLOTPATH will add the obstructions to the elevation file at points along the graph that are right-clicked by the user. The path loss will immediately recalculate to show the effect of the new obstruction. If the path is saved to disk with obstructions added, the obstructions will appear in the path when it is reloaded.
When the "Coordinate Screen Tool" box is checked, place the mouse over the point in question and the computer will deliver the coordinates of the point along the path. These coordinates can then be checked against the best available source for elevation such as a 1:24,000 topographic base map. This feature can be used when the path scrapes over an obstruction and the user desires to determine the coordinates of a given location so that the elevation from a 7 1/2' topographic map may be used.
The Path loss text box shows the total path loss in dB of a selected radio path and does not allow for text entry. Path loss is the sum of the free space loss along a radio path and the obstruction loss, which is automatically calculated. Once the path achieves full free space the obstruction loss will be zero and any increase in antenna height will not result in a reduction of path loss.
PLOTPATH will calculate the path loss for any frequency from 20 MHz to 30 GHz. The frequency of the radio path can be changed by clicking inside the "Freq MHz" text box and by entering a new frequency in megahertz.
The Earth's K factor can be assigned any curvature of the user's choice. The program's default value is set for 4/3 Earth (1.33) that is the commonly used curvature for examining radio paths. Using the value of 1 will set the Earth Curvature at what is commonly called "True Earth." A high Earth Curvature such as ten or over (or the number zero) will set the curvature to a flat Earth value.
The percent of the Fresnel zone plotted along the radio path can be set from the "Fresnel" box. PLOTPATH defaults under original setup to 60 percent, which is the value commonly used for path analysis. Path loss calculations are based on use of 60 percent Fresnel.
The elevation angle text boxes will deliver a constant readout of the elevation angle required of the transmit and receive antennas. These values are determined from the elevations and antenna heights on each end of the radio path.
Click the save command button to save the radio button and text parameter settings so when the program is loaded in the future the new values will be loaded as default values.