ADTRAN 12804108L1A System Manual

Section 2 Microwave Path Engineering Basics TRACER 4108/4208 System Manual16 © 2003 ADTRAN, Inc. 612804208L1-1BHigher levels of fade margin indicate stronger protection against signal fading and a more reliable link. Formost applications, 20 to 30 dB of fade margin should ensure a reliable link.The following sections further discuss the necessary power calculations and their components.4. RECEIVER POWERThe viability of a particular microwave path is determined by the power of the transmitted microwavesignal, the transmit and receive antenna gain, distance, and accumulated system losses (such as RF coaxialcable losses and path loss).The equation relating received signal power to the other microwave parameters isor (in decibel notation)where the variables in the equations are defined asP R received power (dBm)P T transmitted power (adjustable up to 20 dBm maximum)GT transmit antenna gain (decibels referenced to an isotropic source – dBi)GR receive antenna gain (dBi)λ carrier wavelength (meters)d path distance (meters)L other losses (RF coaxial cable, etc. – dB)L P path loss (dB)Figure 1 on page 17 illustrates a wireless link configuration containing all the parameters necessary for thepower budget analysis.When using decibel notation, all quantities must be individually converted to decibelsprior to performing addition and subtraction.PRPTGTGRλ24π( )2d2L------------------------------= (Watts, W)(decibels referenced to a milliwatt, dBm)P R = PT + GT + GR - L - L P