In the video intermediate-frequency (IF) strip of a color television receiver, which types of frequency traps are commonly used to shape the response and reject unwanted components?
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AShunt traps only
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BSeries traps only
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CAbsorption traps only
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DAll of the above
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ENone of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Color TV IF strips must pass the desired video spectrum while rejecting the sound carrier, the color subcarrier image components, and adjacent-channel interference. Traps are frequency-selective networks added to notch out specific frequencies without unduly distorting the video passband.
Given Data / Assumptions:
- Receiver is a color TV with a standard video IF around 38.9–45.75 MHz (standard-dependent).
- Different traps (series, shunt, absorption) can be used.
Concept / Approach:
Shunt and series traps implement notch responses with different insertion behaviors. Absorption traps (loosely coupled resonators) absorb energy at unwanted frequencies to create a deep notch while minimally disturbing adjacent passband regions. In practice, designers mix these techniques to achieve the required response template.
Step-by-Step Solution:
Identify unwanted lines (e.g., sound carrier spur, chroma-related components, adjacent channel).Choose traps: shunt for shunting unwanted frequency to ground; series to block the unwanted path; absorption for a broad, controlled notch.Combine as needed to meet the channel mask and preserve luminance/chrominance fidelity.Verification / Alternative check:
Service manuals and classic IF design texts show multiple trap types in one IF strip to precisely shape the response curve.
Why Other Options Are Wrong:
- Limiting to one trap type rarely meets stringent mask requirements.
- “None” contradicts standard IF design practice.
Common Pitfalls:
Believing a single trap type suffices; underestimating the role of coupling factor and Q in realizing deep, narrow notches without ringing.
Final Answer:
All of the above