RF vs IF
This page describes difference between RF(Radio Frequency) and IF(Intermediate Frequency). It also explains how one frequency is converted to the other and viceversa.
Both the terms are used in wireless system, IF to RF and RF to IF conversion can be done using a device called mixer. The same conversion can be achieved by way of single conversion or dual conversion.
IF to RF conversion is achieved using a RF device called Up-converter. Refer design of up converter using mixers, LOs, amplifiers and other discrete components. This concept is used to convert IF signal to RF signal.
RF to IF conversion is achieved using a RF device called Down-converter. Heterodyne and homodyne receiver architectures are used to convert modulated RF signal to IF signal. Superheterodyne uses 10.7MHz as first IF and 470KHz as second IF.
Following table mentions intermediate frequencies(IF) typically used for different applications such as RF test Equipments, Radar, Satellite equipments, microwave equipments, AM/FM radio, television(TV) etc.
| Type of application | Intermediate Frequency value |
|---|---|
| RF test equipments | 21.4MHz, 160MHz, 310.7MHz |
| Radar | 30MHz |
| Satellite Equipments | 70MHz for C band up converter and down converter; 140MHz for Ku Band; 950 to 1450MHz for L Band Equipments and Systems |
| Microwave Equipments | 70MHz, 75MHz, 250MHz |
| AM Radio(Values are in KHz) | 450,455,460, 465,467,470, 475,480 |
| FM Radio | 262KHz,455KHz, 1.6MHz,5.5MHz, 10.7MHz,10.8MHz, 11.2MHz,11.7MHz, 11.8MHz,21.4MHz, 75MHz,98MHz. |
| Analog Television | 41.25MHz for audio and 45.75MHz for video in TV system M; 33.4MHz(Aural) and 38.9MHz(Visual) in TV system B |
| Broadcast Receiver | 110KHz |
Following block diagram converts IF frequency to RF frequency. This circuit is known as IF to RF converter or RF up converter.
The circuit consists of discrete rf components such as RF mixers, rf filters, rf isolators, chip resistors and capacitors, MMICs etc. Refer RF Frequency Converter design>> and RF Transceiver design and development>> for more information.
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