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收信机的内部噪声不外乎:第一,电路中热骚动产生的无规噪声;第二,电子管内电子流的散弹噪声;第三,周围电磁场感应的噪声等等.这些噪声一般具有能量平均分布的频谱,影响着收信机的有效灵敏度以及移频收信机的阈值.收信机接收弱信号的能力可借测量其线性放大部分的噪声系数来衡量.且收信机输出端的噪声频谱的形状与设备有限的频谱响应特性平方的形状是相同的.在有限通频带内的噪声功率,可用噪声系数来表示.噪声信号发生器和均方值指示器是测量收信机噪声系数较简捷的仪器.本文拟介绍噪声信号发生器和均方值指示器的工作原理、制作方法与收信机噪声系数的测量,供有关从事测试和维护收信机工作的参考.
The internal noise of the receiver is nothing more than: first, the random noise generated by the thermal ripple in the circuit; second, the shot noise of the electron flow in the electron tube; third, the noise induced by the surrounding electromagnetic fields, etc. These noises generally have The average energy distribution of the spectrum affects the receiver’s effective sensitivity and the threshold of the frequency-shifted receiver. The ability of the receiver to receive weak signals can be measured by measuring the noise figure of the linearly amplified portion of the receiver The shape of the noise spectrum is the same as the shape of the square of the spectral response of the device with limited characteristics.The noise power in the limited pass band can be expressed as the noise figure.The noise signal generator and the mean square indicator measure the receiver noise figure Simpler instrument.This article intends to introduce the noise signal generator and mean square indicator of the working principle, method of production and receiver noise figure measurement for the relevant engaged in testing and maintenance of the receiver work reference.