[Elecraft] Vrms measurements with oscilloscope

[Don Brown]

Hi

You should measure the peak to peak voltage divide by 2 and then divide by the square root of 2. A quicker way is to multiply the peak to peak reading by .3535. The conversion only works for sine waves. It will not be correct for digital signals, square waves, pulses or just about anything but sine waves. Many DVMs can measure true RMS on non sine wave signals but the upper frequency limit on DVMs is usually in the audio range. The RF probe detects the RF and converts it to a DC equivalent of the RMS voltage so it can be read on a DVM. The RF probe is also only accurate on sine waves so if you are comparing readings made with a RF probe to readings made with a scope and converted to RMS they will only match on sine waves.


Don Brown
KD5NDB 
  ----- Original Message ----- 
  From: GS<mailto:gerhardschwanz at yahoo.de> 
  To: Mailingliste Elecraft<mailto:elecraft at mailman.qth.net> 
  Sent: Wednesday, June 23, 2004 7:30 AM
  Subject: [Elecraft] Vrms measurements with oscilloscope


  Hi,

  if I signal trace with my oscilloscope and want to
  know the Vrms values at certain points in my K2...

  ... is ist correct to measure the amplitude (not peak
  to peak) of the signal and then divide by the square
  root of 2?

  Will I get values I can check against the given Vrms
  values in the manual?

  Thanks

  Gerhard







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