The local oscillator of a broadcast receiver is tuned to a frequency higher than the incoming frequency

Solution (By Examveda Team)

The question is about the tuning of the local oscillator in a broadcast receiver and why it is tuned to a frequency higher than the incoming frequency. Let's break this down.

Local Oscillator in Radio Receivers:
In radio receivers, the local oscillator (LO) is an electronic oscillator used to convert the incoming radio frequency (RF) signal to an intermediate frequency (IF). The local oscillator produces a frequency that is mixed with the incoming signal to create a frequency that can be more easily processed by the receiver’s circuits. This frequency mixing process is known as heterodyning.

Intermediate Frequency (IF):
The intermediate frequency (IF) is a fixed frequency that is used for easier signal processing. It is derived by mixing the local oscillator frequency with the received signal. The choice of IF allows the receiver to have more stable and simpler amplification and filtering circuits.

Explanation of the Correct Answer:
Option C: Because otherwise an intermediate frequency could not be produced
The correct answer is Option C. The reason the local oscillator is tuned to a frequency higher than the incoming frequency is to create the necessary intermediate frequency (IF). When the local oscillator frequency is set higher than the incoming frequency, the difference between the two frequencies results in a fixed IF. This IF is easier to process for amplification and filtering, which is essential for the proper functioning of the receiver. If the local oscillator were not tuned higher, it would be impossible to generate this intermediate frequency through mixing.

Other Options:
Option A: To help the image frequency rejection
This option is not correct. The rejection of the image frequency is important in superheterodyne receivers, but it is not directly related to tuning the local oscillator higher. The image frequency rejection is typically handled by employing additional filtering and design techniques in the receiver circuitry, rather than simply tuning the local oscillator higher.

Option B: To permit easier tracking
This option is also incorrect. Tracking refers to the ability of the receiver’s circuits to follow the varying frequencies of a station. While easier tracking is important in some contexts, tuning the local oscillator higher than the incoming frequency is done for the purpose of generating the intermediate frequency (IF), not specifically for tracking.

Option D: To allow adequate frequency coverage without switching
This option is not correct either. The local oscillator is tuned higher than the incoming frequency to generate the intermediate frequency, not to avoid switching between frequencies. Frequency coverage and tuning strategies are achieved through the overall design of the receiver circuits, not by simply setting the local oscillator frequency in a particular way.

In conclusion, the local oscillator is tuned to a frequency higher than the incoming frequency to produce the intermediate frequency (IF) (Option C), which simplifies the subsequent stages of signal processing in the receiver.