Match the items in communication systems: (A) Ring modulator, (B) VCO (Voltage-Controlled Oscillator), (C) Foster–Seeley discriminator, (D) Mixer — with their primary functions: (1) Clock recovery, (2) Demodulation of FM, (3) Frequency conversion, (4) Summing of two points, (5) Generation of FM, (6) Generation of DSB-SC.

Introduction / Context:
Communication systems rely on distinct building blocks, each serving a well-defined role in modulation, demodulation, frequency translation, or timing. This matching exercise checks whether you can associate common RF/communication components with their hallmark functions: ring modulators for suppressed-carrier generation, VCOs for frequency generation/modulation, Foster–Seeley discriminators for FM demodulation, and mixers for heterodyning (frequency conversion).

Given Data / Assumptions:

• (A) Ring modulator
• (B) VCO (Voltage-Controlled Oscillator)
• (C) Foster–Seeley discriminator
• (D) Mixer
• Possible roles: (1) clock recovery, (2) FM demodulation, (3) frequency conversion, (4) summing, (5) FM generation, (6) DSB-SC generation

Concept / Approach:

A ring modulator (a balanced modulator) multiplies two signals and cancels the carrier, producing a double-sideband suppressed-carrier (DSB-SC) output. A VCO produces a frequency proportional to a control voltage; by driving that control line with the modulating signal, it generates frequency modulation (FM). The Foster–Seeley discriminator is a classic frequency-to-voltage detector used for narrowband FM demodulation. A mixer multiplies two sinusoids, producing sum and difference frequencies, enabling up/down conversion in superheterodyne receivers and transmitters.

Step-by-Step Solution:

Verification / Alternative check:

Textbook transmitter chains: balanced modulator for DSB-SC, optional carrier reinsertion for AM; FM transmitters employ VCOs or indirect modulation loops. Receiver IF strips commonly use Foster–Seeley (or ratio detectors) for FM detection. Mixers are ubiquitous in front ends (RF→IF) and in transmit chains (IF→RF).

Why Other Options Are Wrong:

(1) Clock recovery is typically a role of PLLs/CR circuits, not ring modulators or mixers directly. (4) Simple summing is performed by adders/combiners, not ring modulators. Swapping VCO and discriminator confuses generation with detection.

Common Pitfalls:

Assuming any multiplier equals a “mixer” in all contexts; forgetting that balanced modulators suppress the carrier; confusing PLL-based FM synthesis with the discriminator’s detection role.

Final Answer:

A-6, B-5, C-2, D-3