Question
Which mixer input is varied or tuned to convert signals of different frequencies to an intermediate frequency (IF)?
Answer Options
- A) Image frequency
- B) Local oscillator
- C) RF input
- D) Beat frequency oscillator
Correct Answer: B
Explanation
In a superheterodyne receiver architecture (the most common type), the mixer stage is used to convert the received Radio Frequency (RF) signal to a fixed, lower frequency called the Intermediate Frequency (IF). This conversion is essential for providing high-quality, fixed-frequency filtering and amplification.
To convert a variable input RF frequency to a fixed IF frequency, the mixer requires a separate input signal whose frequency is varied: the Local Oscillator (LO). The LO frequency is tuned such that the difference (or sum) between the RF signal and the LO signal is always equal to the fixed IF frequency. For example, if RF - LO = IF, then as the operator tunes the receiver (changing RF), the LO must change frequency to keep IF constant.
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