The spectrum analyzer is a special test set, originally developed purely for radar purposes. Today, it is used for many other purposes, but remains a major part of the test equipment collection at any radar facility. The spectrum analyzer is particularly necessary in the maintenance of klystron power-amplifier systems, as tuning of the klystron and driving circuits directly affects the transmitted spectrum

See figure 10 11. The spectrum analyzer is a frequency-domain device, which means that the display has no direct relationship to the radar system timing, and may not be directly interpreted in terms of radar range, or echo time in microseconds. Some spectrum analyzers do have a time-domain feature, but this is an auxiliary function, and not the major purpose.

Figure 10 11: Time v Frequency Domains.

The major purpose of the spectrum analyzer is to serve as a superheterodyne, swept-frequency, receiver. In many uses of the analyzer, it is actually connected to antennas, for the purpose of analyzing environmental electromagnetic radiation, and for locating transmitters. It provides a display, from left to right, of a selected band of frequencies, the presence of which will cause a vertical deflection. When used in the maintenance of the radar system, the analyzer is connected to the INCIDENT waveguide directional coupler. Since the analyzer is a delicate and sensitive receiver, considerable front-end attenuation, ordinarily, must be inserted before the connection is niade. Once connected, and properly adjusted, the spectrum created by the pulse modulation, described in the preceding explanation,...