3.4 Dynamic Range

The idea of dynamic range is simple to convey: it is the ratio of the largest signal amplitude that the receiver can process to the smallest signal amplitude that the receiver can instantaneously process. However, the words can process are troublesome to define. The smallest signal that can be analyzed depends on what the analysis process is like and what its purpose is. Clearly, a precision phase measurement within the pulse requires a larger signal than simply stating that a pulse has crossed a threshold. Likewise, the largest signal that can be tolerated also depends on the measurement being made. Making a precise ERP measurement when the radar s main beam is pointed toward the intercept receiver requires that saturation be minimized; whereas a frequency measurement can be made after a limiter and saturation is of little importance if only one signal is present. Receiver dynamic range must be measured under a variety of conditions, but the conditions must be carefully delineated to avoid confusion and to be certain that a particular receiver can perform a particular function. In a simple test the minimum signal might be determined in the same way as the sensitivity is specified, and the maximum signal level might be that for the 1-dB compression point. This point is illustrated in Figure 3.3. In the linear portion of the input-output transfer characteristic, a 1-dB change in the input level produces a 1-dB change in the output level. As the input level increases,...