Contents - Index


Signal Level

For the active satellite, the program will try and prodice the signal level at the ground.  To do this, it needs to know the power radiated by the satellite (ERP - effective radiated power) expressed in dBm (decibels above 1 milliwatt), and the path loss which depends on the length of the path (i.e. satellite range R km) and the frequency, F MHz.  The formula used in WXtrack is a simple one which is reasonably accurate:

      path_loss := 92.45 + 20 * log10 (Range * F / 1000)

You can specify the operating frequency and ERP for satellites in which you are interested in the file TLEnotes.txt, which includes an explanation of the data format.  If you omit the power level, +33.5dBm is assumed, the value for a typical NOAA APT transmission at 137.5MHz.  The results are in dBm, and would need to be modified by the antenna characteristics to obtain the actual signal level at the antenna terminals.