ADTRAN 12804108L1A System Manual

TRACER 4108/4208 System Manual Section 2 Microwave Path Engineering Basics612804208L1-1B © 2003 ADTRAN, Inc. 17Figure 1. Example Microwave Path with ParametersThe following sections further discuss the power budget analysis and its components.Antenna GainActual transmit and receive antenna gain values depend strictly upon the physical characteristics of theantennas installed for each link. In other words, the size of the dish determines the antenna gain. Using aparabolic dish antenna results in the best performance. Antenna gains are specified in terms of decibels ofgain referenced to an isotropic source (dBi). An isotropic source is a hypothetical antenna having equalradiation in all directions. Typical antenna gains are listed in Table 1; however, dish manufacturers canprovide gains for specific types of antennas.Transmitted Power (PT )The FCC specifies the maximum transmitter power that may be used for antennae of a given gain. FCCRules Part 15, Subpart 247 allow for a maximum power of 1 Watt (30 dBm) into antennae of a gain lessthan or equal to 6 dBi. At 2.4 GHz (TRACER 4108), the 1-watt maximum transmitter power must bereduced by 1 dB for every 3 dB of antenna gain over 6 dBi. Since the TRACER 4108 maximum transmitpower is 100 milliwatts, only antennas with gains above 36 dBi (12-foot diameter parabolic dishes) requireany reduction in transmit power. For the 5.8 GHz band (TRACER 4208), there is no reduction intransmitter output power required for antenna gains greater than 6 dBi.Table 1. Antenna Gain for Given Dish DiametersDish Diameter(in feet)Gain at 2.4 GHz(in dBi)Gain at 5.8 GHz(in dBi)2 21 28.54 27 34.26 31 37.58 33 40.710 35 42.512 37 44.2G T G Rd, LPP T P RλLL