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E7F14

PRACTICAL CIRCUITS · Software defined radio fundamentals: digital signal processing (DSP) filtering, modulation, and demodulation; analog-digital conversion; digital filters

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Which of the following would allow a digital signal processing filter to create a sharper filter response?

  1. AHigher data rate
  2. BMore taps
  3. CLower Q
  4. DDouble-precision math routines
Why A digital filter computes its output by multiplying a series of stored input samples by coefficients and summing them; each stored sample and coefficient pair is a tap. More taps means the filter has more degrees of freedom to shape the frequency response, giving steeper skirts and better stopband rejection, at the cost of more computation and more delay. Roughly, transition-band sharpness improves in proportion to filter length, so doubling the taps roughly halves the transition width.
Watch out Double-precision math improves numeric accuracy and reduces rounding noise, but it does not make the response steeper; a higher sample rate actually spreads the same number of taps over a wider bandwidth, which tends to make a filter less selective for a given passband.
Taps are like poles in an analog filter: more taps, steeper skirts.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of E7F

  1. E7F01 What is meant by "direct sampling" in software defined radios?
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  7. E7F07 What function is performed by a Fast Fourier Transform?
  8. E7F08 What is the function of decimation?
  9. E7F09 Why is an anti-aliasing filter required in a decimator?
  10. E7F10 What aspect of receiver analog-to-digital conversion determines the maximum receive bandwidth of a direct-sam…
  11. E7F11 What sets the minimum detectable signal level for a direct-sampling software defined receiver in the absence …
  12. E7F12 Which of the following is generally true of Finite Impulse Response (FIR) filters?
  13. E7F13 What is the function of taps in a digital signal processing filter?
  14. E7F14 Which of the following would allow a digital signal processing filter to create a sharper filter response?
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