TABLE OF CONTENTS Chapters 11 and 12 described how the input signals are separated in the frequency domain through channelization. This chapter describes how, after the frequency channelization, further processing is performed to determine the number of frequencies and the frequencies themselves. The frequency data resolution (or frequency bin width) calculated through an FFT operation determines the frequency precision measured on the input signal. It is often desirable to obtain better frequency precision than the FFT operation can provide. This is especially true for the 32-point FFT discussed in Chapter 11, which produces a frequency data resolution of 93.75 MHz with a 3-GHz sampling frequency. Another problem with such a wide frequency bin is that when two signals fall into one frequency output channel, the receiver cannot effectively separate them. In other words the two-signal frequency resolution is only about 93.75 MHz.
The traditional way to separate signals by frequency is through an analog filter bank. Although the main emphasis of this book is digital, one still can consider the analog filtering approach. In an analog channelized receiver, after the filter bank and amplifier, crystal video detectors are used to convert the radio frequency (RF) into video signals. The video signals are digitized by ADCs and are further processed to determine the number of signals and their frequencies. In converting RF into video signal, some information is lost. If two signals fall into one channel, it is difficult to separate them.
In a digital receiver ADCs can be used after an...
