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E5A12

ELECTRICAL PRINCIPLES · Resonance and Q: characteristics of resonant circuits; series and parallel resonance; definitions and effects of Q; half-power bandwidth

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What is the half-power bandwidth of a resonant circuit that has a resonant frequency of 3.7 MHz and a Q of 118?

  1. A436.6 kHz
  2. B218.3 kHz
  3. C31.4 kHz
  4. D15.7 kHz
Why Half-power (-3 dB) bandwidth of a resonant circuit is BW = f0 / Q. With f0 = 3.7 MHz and Q = 118, BW = 3,700,000 / 118 = 31,356 Hz, about 31.4 kHz. Higher Q means a narrower, sharper response for the same resonant frequency.
Watch out The 436.6 kHz figure comes from multiplying 3.7 MHz by 118 instead of dividing, and 15.7 kHz is that correct result cut in half, as if the formula used 2Q.
BW = f divided by Q. Q is quality, and high quality means narrow. Divide, never multiply.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of E5A

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  4. E5A04 What is the magnitude of the impedance of a parallel RLC circuit at resonance?
  5. E5A05 What is the result of increasing the Q of an impedance-matching circuit?
  6. E5A06 What is the magnitude of the circulating current within the components of a parallel LC circuit at resonance?
  7. E5A07 What is the magnitude of the current at the input of a parallel RLC circuit at resonance?
  8. E5A08 What is the phase relationship between the current through and the voltage across a series resonant circuit a…
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  10. E5A10 What is the resonant frequency of an RLC circuit if R is 33 ohms, L is 50 microhenries, and C is 10 picofarad…
  11. E5A11 What is the half-power bandwidth of a resonant circuit that has a resonant frequency of 7.1 MHz and a Q of 15…
  12. E5A12 What is the half-power bandwidth of a resonant circuit that has a resonant frequency of 3.7 MHz and a Q of 11…
  13. E5A13 What is an effect of increasing Q in a series resonant circuit?
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