ADTRAN 12804108L1A System Manual

TRACER 4108/4208 System Manual Section 2 Microwave Path Engineering Basics612804208L1-1B © 2003 ADTRAN, Inc. 151. LINE-OF-SITEThe TRACER 4108 and 4208 systems are designed for operation in the license-free 2.400 to 2.4835 GHzand 5.725 GHz to 5.850 GHz industrial, scientific and medical (ISM) bands, respectively. Radio wavepropagation in these bands exhibit microwave characteristics which are ideally suited for point-to-point,line-of-sight communications. Line-of-Sight requires that the transmitting antenna and receiving antennaare able to “see” each other, and that the straight-line path between the two antennas is free of obstructions,such as buildings, trees, mountains, and, in longer paths, even the curvature of the earth. In addition, formaximum signal strength the area around the visual line-of-sight where microwave signals reflect (Fresnelzone) must also be free of obstructions. Fresnel zones are discussed in more detail on page 22.Terminology2. DECIBELSUnderstanding the decibel (dB) format is key when discussing microwave path engineering because thereceived signal power is often expressed in decibel format. In general, any quantity can be expressed indecibels. If the quantity x is a power level (in Watts), the decibel equivalent is defined asIf the quantity x is referenced to a milliwatt (mW), then the decibel-milliwatt (dBm) is used instead of ageneric decibel.Using the decibel format simplifies power calculations by reducing multiplication and division operationsinto addition and subtraction operations.3. CALCULATING THE FADE MARGINThe fade margin (F ) is a value indicating the amount of extra signal power available to the receiver tooperate at a maximum bit error rate (BER). Fade margin is simply the difference between the availablesignal power at the receiver (P R ) and the receiver sensitivity (P sens ).Point-to-Point Wireless communication from a single site to another individualsite. Contrast with point-to-multipoint.Line-of-Sight An unobstructed, direct path exists between the transmitting andthe receiving antennas.It is imperative to determine if the proposed microwave path is suitable (at a minimum) forideal, nondistorted signals before attempting installation.xdB 10 log10 x( )⋅= (dB)xdBm 10 log10x1mW-------------  ⋅= (dBm)F PR Psens–= (dB)