In superheterodyne receiver alignment, a ‘‘padder’’ is used in the local oscillator section. What is a padder electrically, as used for low-end tracking adjustment?

Introduction / Context:
Receiver tracking aligns the RF tuned circuit and the local oscillator (LO) so that their frequency relationship remains correct across the tuning range. A padder is added to the LO circuit to correct low-frequency tracking errors in superheterodyne receivers.

Given Data / Assumptions:

• The padder sits in the LO tuned network.
• Used to correct low-end dial calibration/tracking.
• Component is adjustable during alignment.

Concept / Approach:

Tracking errors arise because the tuning capacitances and inductances do not vary perfectly with frequency. A padder capacitor (often in series) fine-tunes the effective capacitance at the low-frequency end of the band, aligning the LO with the RF input circuit across the dial. This improves image rejection and frequency accuracy.

Step-by-Step Solution:

Verification / Alternative check:

Service manuals specify “padder” adjustments at the low end of the band while “trimmer” capacitors are typically used for the high end; both are capacitors.

Why Other Options Are Wrong:

• Insulator/varistor/variable resistor: not used for LO tracking.
• Inductor: coils affect tracking but the named “padder” is specifically a capacitor.

Common Pitfalls:

Confusing the padder (low-end) with the trimmer (high-end) capacitor; both are capacitive adjustments but serve different parts of the dial.

Final Answer:

A capacitor (usually variable or adjustable) used for tracking