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四、带宽选择测量中,对IF带宽(也称分辩率带宽)都有具体要求,但MIL-STD-461和462对比并未作规定,所以设计测试时,必须确定最佳带宽,这将涉及许多因素。比如,接收机的灵敏度,本振(LO)的馈入电平、天线特性及电缆损耗。首先分析最简单的情形——窄带测量。由于窄带信号的幅值与接收机带宽无关,故可选择使接收机信噪比最大的带宽。接收机产生的噪声是不相关的宽带噪声,其值按每十倍频程10dB 增加,如式(1)噪声值变化(dB)=10 log(BW_1/BW_2) (1)因此,接收机内可获得的最小带宽提供了窄带测量的最佳灵敏度。实际上,最小带宽并非最佳选择。带宽对测量速度的影响是必须考虑的因素。接收机的扫描时间与带宽平方成正比,见式(2)
Fourth, the bandwidth selection measurement, the IF bandwidth (also known as the resolution bandwidth) have specific requirements, but MIL-STD-461 and 462 contrast is not specified, so the design test, you must determine the best bandwidth, which will involve Many factors For example, receiver sensitivity, LO feed-in level, antenna characteristics and cable loss. First analyze the simplest case - narrowband measurement. Since the amplitude of the narrowband signal has nothing to do with the receiver bandwidth, the bandwidth that maximizes the receiver’s signal-to-noise ratio can be chosen. The noise generated by the receiver is an uncorrelated wideband noise whose value is increased by 10 dB per decade, as shown in Equation (1). The change in noise value (dB) = 10 log (BW_1 / BW_2) The minimum achievable bandwidth provides the best sensitivity for narrow-band measurements. In fact, the minimum bandwidth is not the best choice. The impact of bandwidth on the measurement speed is a factor that must be considered. The receiver scan time is proportional to the square of the bandwidth, see equation (2)