Popular intermediate frequencies (IF) for microwave and radar receivers operating in the 1–10 GHz RF range are typically which of the following?
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A30, 60 and 70 kHz
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B3, 6 and 7 kHz
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C30, 60 and 70 MHz
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D3, 6 and 7 GHz
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E1.6, 4.5 and 10.7 MHz
Answer
Correct Answer: 30, 60 and 70 MHz
Explanation
Introduction / Context:Microwave and radar receivers use down-conversion from gigahertz RF to a convenient IF where filtering and amplification are practical. Standardized IFs simplify filter design and system interoperability.
Given Data / Assumptions:
- RF range: 1–10 GHz (L-, S-, C-, X-bands).
- Need IF high enough to separate images yet low enough for high-performance filters.
Concept / Approach:
Common IFs for microwave superhets include ~30 MHz, ~60 MHz, and ~70 MHz (and their near variants). These strike a balance between image rejection, filter availability (crystal/SAW), and achievable IF gains.
Step-by-Step Solution:
High RF (GHz) → mixer with LO → fixed IF (tens of MHz).Select IF values with mature filter tech (e.g., 70 MHz SAW/crystal filters).Achieve narrow, stable passbands and good dynamic range.Verification / Alternative check:
Radar/receiver literature and module catalogs list 30/60/70 MHz IF chains as industry staples.
Why Other Options Are Wrong:
- kHz IFs are far too low for modern microwave selectivity demands.
- GHz IFs defeat the purpose of down-conversion.
- 1.6/4.5/10.7 MHz are common in other contexts (e.g., 10.7 MHz for FM), not typical for microwave radar IF back-ends.
Common Pitfalls:
- Assuming FM broadcast IF (10.7 MHz) is universal; microwave systems prefer higher IFs.
Final Answer:
30, 60 and 70 MHz