IF Bandwidth

IF Bandwidth is a range of frequencies centered around the IF frequency, limited by the 3dB amplitude points.

Intermediate frequencies are used for three general reasons. At very high (gigahertz) frequencies, signal processing circuitry performs poorly. Active devices such as transistors cannot deliver much amplification (gain). Ordinary circuits using capacitors and inductors must be replaced with cumbersome high frequency techniques such as striplines and waveguides. Therefore, a high frequency signal is converted to a lower IF for more convenient processing.

For example, in satellite dishes, the microwave downlink signal received by the dish is converted to a much lower IF at the dish, to allow a relatively inexpensive coaxial cable to carry the signal to the receiver inside the building. Bringing the signal in at the original microwave frequency would require an expensive waveguide.

A second reason, in receivers that can be tuned to different frequencies, is to convert the various different frequencies of the stations to a common frequency for processing.

However, 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. With all known filtering techniques, the filter's bandwidth increases proportionately with the frequency. Accordingly, a narrower bandwidth and more selectivity can be achieved by converting the signal to a lower IF and performing the filtering at that frequency.