Question
Download Solution PDFThe appropriate value of modulation index β for transition between narrow band and wide band FM is considered as:
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
Narrow-Band Frequency Modulation (NBFM):
- For NBFM, the modulation index (β) is less than 1.
- NBFM has a smaller bandwidth and spectrum consisting of a carrier, upper sideband, and lower sideband.
- This system is used in FM mobile communications such as police wireless, ambulances, taxicabs, etc.
- Figure of Merit for NBFM = \(1 \over 3\)
Wide-Band Frequency Modulation (WBFM):
- For WBFM, the modulation index (β) is greater than 1.
- WBFM has a large bandwidth and spectrum consisting of a carrier and infinite number of sidebands.
- The total power is independent of the modulation index.
- Figure of Merit for WBFM = \({3 \over 2}β ^2\)
Calculation:
For FM system, NBFM offers improved noise performance over WBFM when
\({3 \over 2}β ^2 > {1 \over 3}\)⇒\(β > \sqrt{2/3} = 0.471\)
Hence, β = 0.471 is defined as the transition between narrow band FM and wide band FM.
Last updated on Jun 12, 2025
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