Vrms measurements with oscilloscope

[GS-3]

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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[JEAN-FRANCOIS MENARD-2]

I have the same concern about these mesurements. I bought a Fluke 123
yesterday that read true rms values.

I cannot get the range of value like in the manual... If someone could
provide us some readouts using the standard RF in the kit and also for the
same place, the readouts in Vrms with a scope would be really appreciated.


-----Message d'origine-----
De : [hidden email]
[mailto:[hidden email]] De la part de GS
Envoyé : 23 juin 2004 08:31
À : Mailingliste Elecraft
Objet : [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



       

       
               
___________________________________________________________
Bestellen Sie Y! DSL und erhalten Sie die AVM "FritzBox SL" für 0€. Sie
sparen 119€ und bekommen 2 Monate Grundgebührbefreiung.
http://de.adsl.yahoo.com _______________________________________________
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[Don Brown-4]

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:[hidden email]>
  To: Mailingliste Elecraft<mailto:[hidden email]>
  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







  ___________________________________________________________
  Bestellen Sie Y! DSL und erhalten Sie die AVM "FritzBox SL" für 0?.
  Sie sparen 119? und bekommen 2 Monate Grundgebührbefreiung.
  http://de.adsl.yahoo.com<http://de.adsl.yahoo.com/>
  _______________________________________________
  Elecraft mailing list
  Post to: [hidden email]<mailto:[hidden email]>
  http://mailman.qth.net/mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
  You must subscribe to post.
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[Don Brown-4]

Hi

What is really needed is a troubleshooting guide with waveshape and amplitude pictures of the readings taken with a scope or at least peak to peak readings at the same test points used for the RF probe. A scope inherently measures peak to peak or ground to peak (which is just another form of peak to peak). Trying to get meaningful readings to correlate with a RF probe is not going to work very well unless the waveshape is a pure sine wave.

Your Fluke will measure true RMS but not at RF frequencies. Most DVMs only have a bandwidth of 10-20 KHz on AC.


Don Brown
KD5NDB
   
  ----- Original Message -----
  From: Jean-François Ménard<mailto:[hidden email]>
  To: 'Mailingliste Elecraft'<mailto:[hidden email]>
  Sent: Wednesday, June 23, 2004 7:47 AM
  Subject: RE : [Elecraft] Vrms measurements with oscilloscope


  I have the same concern about these mesurements. I bought a Fluke 123
  yesterday that read true rms values.

  I cannot get the range of value like in the manual... If someone could
  provide us some readouts using the standard RF in the kit and also for the
  same place, the readouts in Vrms with a scope would be really appreciated.


  -----Message d'origine-----
  De : [hidden email]<mailto:[hidden email]>
  [mailto:[hidden email]] De la part de GS
  Envoyé : 23 juin 2004 08:31
  À : Mailingliste Elecraft
  Objet : [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







  ___________________________________________________________
  Bestellen Sie Y! DSL und erhalten Sie die AVM "FritzBox SL" für 0€. Sie
  sparen 119€ und bekommen 2 Monate Grundgebührbefreiung.
  http://de.adsl.yahoo.com<http://de.adsl.yahoo.com/> _______________________________________________
  Elecraft mailing list
  Post to: [hidden email]<mailto:[hidden email]>
  http://mailman.qth.net/mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
  You must subscribe to post.
  Subscriber Info (Addr. Change, Unsub etc):
  http://mailman.qth.net/subscribers.htm<http://mailman.qth.net/subscribershtm>
  Elecraft page: http://www.elecraft.com<http://www.elecraft.com/>


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