1.3 Limitations Due to Noise 噪声对ELINT接收机的限制

Although in the usual situation the intercept receiver enjoys a considerable range advantage over the radar, this does not mean that the ELINT signal analyst has the luxury of a high signal-to-noise ratio (SNR). The situation is frequently just the reverse, as the ELINT site attempts to receive signals located at great distances or beyond the radar horizon – possibly due to national boundaries that cannot be crossed. It is therefore typical for an ELINT station to be equipped with very low noise front-end amplifiers. High gain antennas that can be steered may also be used at the price of decreased probability of interception. It is also typical to locate sites at high altitudes and to use airborne platforms. The potentially large ratio of ELINT range-to-radar for long-range radar systems often means that the limiting factor in receiving signals from a radar is the reduction in signal strength due to the curvature of the Earth.

  In many cases, the ingenuity of the ELINT signal analyst is severely taxed by a low SNR. The limitations due to low SNR arise repeatedly in the following chapters. No matter what clever signal analysis technique is devised, the fundamental limits due to noise remain.

  这一节实在很短小，只有两段文字，里面有价值的东西几乎没有，也许它的题目就已经说明了一个不可忽视的事实：只有在足够信噪比的条件下，我们的ELINT信息处理（这一任务由数字信号处理设备完成）才是有意义的。进一步地，ELINT信号处理的对象是数字信号，是经过模数转换器采样的，而模数转换器之前还有天线和射频接收通道，那么，我们必须要保证进入模数转换器的信号中包含有足够的有效信息，即天线和射频通道的设计是非常关键的。