5-15
Present-day spectrum analyzers can measure segments of the frequency spectra from 0 hertz to as
high as 300 gigahertz when used with waveguide mixers.
SPECTRUM ANALYZER APPLICATIONS
Figure 5-13 shows a typical spectrum analyzer. The previously mentioned measurement capabilities
can be seen with a spectrum analyzer. However, you will find that the spectrum analyzer generally is used
to measure spectral purity of multiplex signals, percentage of modulation of AM signals, and modulation
characteristics of fm and pulse-modulated signals. The spectrum analyzer is also used to interpret the
displayed spectra of pulsed rf emitted from a radar transmitter.
Figure 5-13.—Typical spectrum analyzer.
COMPLEX WAVEFORMS
Complex waveforms are divided into two groups, PERIODIC WAVES and NONPERIODIC
WAVES. Periodic waves contain the fundamental frequency and its related harmonics. Nonperiodic
waves contain a continuous band of frequencies resulting from the repetition period of the fundamental
frequency approaching infinity and thereby creating a continuous frequency spectrum.
MODULATION MEASUREMENTS
In all types of modulation, the carrier is varied in proportion to the instantaneous variations of the
modulating waveform. The two basic properties of the carrier available for modulation are the
AMPLITUDE CHARACTERISTIC and ANGULAR (frequency or phase) CHARACTERISTIC.
Amplitude Modulation
The modulation energy in an amplitude-modulated wave is contained entirely within the sidebands.
Amplitude modulation of a sinusoidal carrier by another sine wave would be displayed as shown in figure
5-14. For 100% modulation, the total sideband power would be one-half of the carrier power; therefore,
