ABSTRACT
A spectrum analyzer is one instrument for gathering information about a signal. Unlike the network analyzer (where the signal frequency is set by the user), information is not available about this signal before measurement. It is obvious that the time domain waveform contains complete information about a signal. But it is not always that all time domain measurements are useful-as will be seen later, time domain measurement using an oscilloscope has its own limitation. Measurement of spectra (power spectral density, for example, which contains only partial information about a signal) also has an equal importance. One direct advantage is measuring the electromagnetic emission. With the overcrowding of the spectrum today, including modern numerous wireless standards like 2G, 3G, EDGE, GSM, LTE, WiMax, etc., in the same frequency band, it is imperative that emissions from the carrier under test do not significantly interfere with signals falling close to the same. One particular example is the emission from your own cell phone interfering with other handsets reusing the same frequency band. The result is something that you would not want, quantified as poor reception and cross talk. Another form of distortion that manifests itself is the distortion of the message modulated onto the carrier. Third-order intermodulation (two tones of a complex signal modulating each other) can be particularly troublesome because the distortion components can fall within the band of interest. This is particularly dangerous as using low-pass filters is not appropriate; the desired signal and the unwanted signal share the same frequency space.
