Area Coverage Prediction (VOAAREA)

VOACAP Quick Guide: Home

 

From a point-to-point circuit analysis we can proceed to an area coverage analysis. It sometimes happens that a frequency that is most suitable for a certain point-to-point circuit, is not the best possible for providing good service to a specific area.

Let us take our example circuit of Pori (Finland) to Johannesburg (South Africa) at 1 UTC in December 2001. We have had an analysis of this circuit in the article Understanding Above-the-MUF Predictions. It shows that the best frequency would be 11.9 MHz. Now let us see how that frequency would work for the African continent.

The following screen reflects the basic settings of VOAAREA - a companion program to VOACAP - needed for running the coverage analysis:

We are interested in the circuit reliability in Africa, therefore we choose REL from Parameters. You may choose several parameters at a time. As some locations in our target area are 10,000 km away, we choose the Method 30, Short/Long Path Model Smoothing. Be sure to select CCIR (Oslo) coefficients (not URSI88). Also, keep the Fprob values as shown above. The following screen shots explain how to set some other input values shown above:

Plot Center

Groups

System

Running the Maps

Choose Run > Calculate > Save{temp.VOA}/Calculate:

When the calculations are done, choose Run > Plot results. A window will appear, choose File > Open TEMP.VG1:

The following window will appear:

To plot the map, just choose Plot to > Window. You can also plot or print the map to the printer. To view the remaining maps, choose File > Open. The file names are of format TEMP.VG? where the question mark is a number between 1 to 7.

Furthermore, in this window you can choose several output parameters for viewing if you did not do so in the main screen. Just select them by clicking the Parameters button.

If you wish to change the colours or values to be plotted, click the Contours button. The following window will appear:

Then click the REL button. The following window will appear:

You can change the values and colours here. Note that a value of -999 is used to fill unused lines. Be sure to select a proper colour for that value too! If you change any of the default values, click the Values assigned are: button. The text AUTO scaled will change to USER defined. Otherwise, your settings will be ignored.

Area Coverage Analysis

Using the output parameter of REL, the Circuit Reliability - the percentage of days in the month when the SNR (SNR50) value will equal to or exceed the REQ.SNR. (67 dB-Hz) - the following coverage maps can be produced for the frequencies of 9.7, 11.9, 13.7 and 15.4 MHz at 1 UTC in December 2001. We see that 9.7 MHz can serve a larger portion of Africa than 11.9 MHz. It also provides better service to Europe. The frequencies of 13.7 and 15.4 MHz can provide service to Southern Africa but their overall performance is not adequate.

9.7 MHz	11.9 MHz	Legend

13.7 MHz	15.4 MHz