The main reason for using an intermediate frequency is to improve frequency selectivity. In communication circuits, a very common task is to separate out, or extract, signals or components of a signal that are close together in frequency. This is called filtering. Some examples are: picking up a radio station among several that are close in frequency, or extracting the chrominance subcarrier from a TV signal. With all known filtering techniques the filter's bandwidth increases proportionately with the frequency. So a narrower bandwidth and more selectivity can be achieved by converting the signal to a lower IF and performing the filtering at that frequency. FM and television broadcasting with their narrow channel widths, as well as more modern telecommunications services such as cell phones and cable television, would be impossible without using frequency conversion.
The main reason for using an intermediate frequency is to improve frequency selectivity. In communication circuits, a very common task is to separate out, or extract, signals or components of a signal that are close together in frequency. This is called filtering. Some examples are: picking up a radio station among several that are close in frequency, or extracting the chrominance subcarrier from a TV signal. With all known filtering techniques the filter's bandwidth increases proportionately with the frequency So a narrower bandwidth and more selectivity can be achieved by converting the signal to a lower IF and performing the filtering at that frequency. FM and television broadcasting with their narrow channel widths, as well as more modern telecommunications services such as cell phones and cable television, would be impossible without using frequency conversion.