EMC Question of the Week: May 25, 2026

sine wave displayed on an oscilloscope

If a 100-MHz sine wave with a measured with a 50-Ω oscilloscope displays a peak amplitude of 2.0 volts. The same signal measured on a 50-Ω spectrum analyzer should have a single narrow-band spike with peak amplitude of  

  1. 6 dB(μV)
  2. 120 dB(μV)
  3. 123 dB(μV)
  4. 126 dB(μV)

Answer

The correct answer is “c.” A spectrum analyzer measures the rms amplitude of sine wave. In this case, the 2 volts-peak corresponds to an rms amplitude of about 1.41 volts. Converted to dB(μV) as displayed on the spectrum analyzer, this is 123 dB(μV).

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