9. the equipment specification referred to as NPR must be listed as the next most important. Equipment NPR affects all of the system G (indB)  20logf(inMHz) characteristics mentioned for System Gain, with the exception of feet) 52.6 (50.18) system availability. Like System Gain, the definition of NPR will be given later and the subject examined further. Antenna gain a D2 (50.19) Let it be said at this point that improvements in both System Gain and NPR are highly sought by both the system designer and the Thus it can be seen that high System Gain may allow the use of equipment designer. Thus, the system requirements influence pro- the minimum size (diameter) dish antenna. This antenna not only gress in equipment design; yet, the status of the equipment design costs less, but decreases stress due to wind loading on the supporting determines the system characteristics. Improvements in both have structure. In this manner, System Gain can reduce system cost and been allowed mainly by advances in microwave semiconductor increase system reliability. technology. Given a path length and antenna size, increased System Gain will increase the level of the signal arriving at the microwave receiver. 50.4.4 System gain For the f.m. microwave receiver, this may improve the S/N ratio in a voice channel, or the BER in a data channel, if the intrinsic noise The microwave equipment performance parameters of transmitter of the radio is not yet the limiting factor. This can be seen from the power output and receiver sensitivity have been combined into a relationship between received level and S/N for an f.m. receiver, as single specification - System Gain. System Gain is the decibel in Equation 50.20, where C is the received level. 139 = (-KTB) in difference between transmitter power and receiver sensitivity. Thus dBm in a 3kHz bandwidth. F is the receiver noise figure. is the higher transmitter power, improved receiver sensitivity, or both, test tone deviation. f mod is the test tone frequency. will give a higher System Gain figure.