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E8A10

SIGNALS AND EMISSIONS · Fourier analysis; RMS measurements; average RF power and peak envelope power (PEP); analog/digital conversion

E8A10E8A →

What is the purpose of a low-pass filter used at the output of a digital-to-analog converter?

  1. ALower the input bandwidth to increase the effective resolution
  2. BImprove accuracy by removing out-of-sequence codes from the input
  3. CRemove spurious sampling artifacts from the output signal
  4. DAll these choices are correct
Why A DAC builds its output from discrete steps at the sample rate, so the waveform is really the desired signal plus copies (images) of it centered on multiples of the sampling frequency, along with the sharp-edged staircase harmonics. A low-pass reconstruction filter set just below the Nyquist frequency (half the sample rate) passes the wanted audio or baseband signal and strips off those higher-frequency sampling artifacts, smoothing the steps into a clean analog waveform.
Watch out The idea about lowering input bandwidth to increase resolution describes anti-alias filtering ahead of an analog-to-digital converter, and resolution is set by the number of bits, not by filtering; nothing in an analog output filter can sort out out-of-sequence digital codes.
DAC out = reconstruction filter: smooth the staircase, kill the images above Nyquist.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
← E8A09 All of E8A E8A11 →

The rest of E8A

  1. E8A01 What technique shows that a square wave is made up of a sine wave and its odd harmonics?
  2. E8A02 Which of the following is a type of analog-to-digital conversion?
  3. E8A03 Which of the following describes a signal in the time domain?
  4. E8A04 What is "dither" with respect to analog-to-digital converters?
  5. E8A05 What is the benefit of making voltage measurements with a true-RMS calculating meter?
  6. E8A06 What is the approximate ratio of PEP-to-average power in an unprocessed single-sideband phone signal?
  7. E8A07 What determines the PEP-to-average power ratio of an unprocessed single-sideband phone signal?
  8. E8A08 Why are direct or flash conversion analog-to-digital converters used for a software defined radio?
  9. E8A09 How many different input levels can be encoded by an analog-to-digital converter with 8-bit resolution?
  10. E8A10 What is the purpose of a low-pass filter used at the output of a digital-to-analog converter?
  11. E8A11 Which of the following is a measure of the quality of an analog-to-digital converter?
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