Three-point tracking is achieved with

Solution (By Examveda Team)

Three-point tracking is a technique used in radio receivers to ensure that the intermediate frequency (IF) remains constant even when the radio frequency (RF) is tuned across the frequency band. It involves adjusting multiple components in the receiver's RF section to maintain this constant IF. Let's define the key term and then discuss the options.

Intermediate Frequency (IF): The IF is a fixed frequency used in a radio receiver after the RF signal is converted down from its original frequency. Using a fixed IF simplifies the design of the amplification and filtering stages. Maintaining a constant IF is crucial for consistent receiver performance across the tuning range.

Correct Answer: B. The padder capacitor
The padder capacitor is a variable capacitor used in conjunction with a trimmer capacitor (or other tuning components) in the RF section of a superheterodyne receiver. It's specifically used for three-point tracking. Three-point tracking involves setting the IF to be correct at three specific points across the tuning range (typically the low, mid, and high frequencies). The padder capacitor helps to compensate for the variations in the RF tuning capacitance and inductance across this range, ensuring the IF remains consistent. By adjusting the padder capacitor, the overall RF resonant circuit's tuning is slightly shifted at each end of the frequency range such that at all three points, the difference between the RF and IF is consistently maintained. This method avoids the need for more complex tracking mechanisms.

Why other options are incorrect:
A. Variable selectivity: Variable selectivity refers to the ability to adjust the bandwidth of the receiver's IF filter. While important for receiver performance, it's not directly related to maintaining a constant IF across the tuning range.
C. Double spotting: Double spotting is a fault in a receiver where two different RF signals are converted to the same IF, resulting in interference. This is a problem to be avoided, not a solution for three-point tracking.
D. Double conversion: Double conversion involves using two IF stages. While this improves image rejection (another important receiver characteristic), it doesn't directly address the issue of maintaining a constant IF during tuning; it's a different design feature.