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目前,噪声系数N_F测量方法有正弦信号发生器法及标准噪声源法。采用正弦信号发生器法时,必须测定系统的噪声带宽、功率增益及输出噪声的均方值,但是这些量精确测定是困难的。其次这些量与源电阻及测试频率有关,所以这种方法不仅麻烦,而且精确度较低。因此目前噪声系数测试仪大多数采用标准噪声源法。图1给出N_F测试原理图。K置于1时,电表指示被测管及源电阻R_S的噪声输出,再把K置于2,则由于3分贝功率衰减器作用使噪声功率衰减一半(功率表指示读数下
At present, the noise factor N_F measurement methods are sinusoidal signal generator method and the standard noise source method. With the sinusoidal signal generator method, the system noise bandwidth, power gain, and mean square of the output noise must be measured, but accurate measurements of these quantities are difficult. Second, these quantities are related to source resistance and test frequency, so this method is not only cumbersome but also less accurate. Therefore, the current noise figure tester most of the standard noise source method. Figure 1 shows the N_F test schematic. When K is set to 1, the meter indicates the noise output from the test tube and the source resistance R_S, and then K is set to 2, the noise power will be attenuated in half due to the effect of the 3 dB power attenuator (the power meter indicates the reading