Electronics Explorer Spectrum Analyzer dBV

[Rick314]

It appears that the Electronics Explorer Spectrum Analyzer amplitude display shows "dB relative to 1V" as relative to 1 Volt peak, but "dBV" as relative to 1 Volt RMS.  Shouldn't they both be relative to 1 Volt peak?

See the two images.  A 1 Vpk sine wave is being displayed on the spectrum analyzer.  In one case, the top of the spectrum analyzer corresponds to "dB relative to 1V" and as expected the signal comes to the top of the image.  So this is dB relative to 1 Vpk.  In the other image the top of the spectrum analyzer corresponds to "0 dBV" and the indicated signal drops by 3 dB.  So this is dB relative to 1 Vrms.  (I found this by expecting a "1V" AWG level setting to correspond to "0 dBV" on the spectrum analyzer, and finding the unexpected -3 dB shift.)

 

[attila]

Hi @Rick314

I understand it now.

Thank you

[attila]

Hi @Rick314

The dBV "standard" is relative to 1Vrms, 1.41Vpeak, 2.83Vpk2pk.
The dB is expressed in the application relative to Vpeak to be in accordance with Wavegen (peak) amplitude adjustment.

[Rick314]

@attila said 'The dBV "standard" is relative to 1Vrms, 1.41Vpeak, 2.83Vpk2pk.'  I agree the spectrum analyzers I know (Hewlett-Packard, Agilent Technologies, Tektronix) do this, so "dBV" meaning dB relative to 1 Vrms makes sense.

But making "dBV" and "dB" "Reference: 1 V" have different meanings in your user interface seems wrong.  The abbreviation "dBV" means "dB relative to 1 Volt" and "dB" "Reference: 1 V" looks like exactly the same thing.  Are you aware of any mainstream spectrum analyzers that interpret "dB" "Reference: 1 V" as meaning dB relative to 1 Vpk instead of dB relative to 1 Vrms?

[attila]

Hi @Rick314

I see now what causes the confusion...
The reference is only valid when it is enabled, when dB is selected, and it is irrelevant for the other units.
For the next release I have modified it to give valid reference values even when it is disabled:

Thank you for the observation.

[Rick314]

Thank you for your help @attila but I do not think I am being understood correctly.  I see that your left image has changed from the bottom image in my original post.  I understand that grayed-out settings don't apply currently.  That isn't the problem.  I don't think replacing grayed-out "1 V" with grayed-out "1 V(+squiggle)" is needed.

My confusion was that I thought your left and right images describe the exact same situation: dB relative to 1 Volt RMS.  I mentioned Hewlett-Packard, Agilent Technologies, and Tektronix spectrum analyzers.  I don't think any of them display dB relative to 1 Volt Peak in any circumstance.  That is where my confusion came from.  But I now understand that the WaveForms user interface uses "1 V" to mean 1 Volt Peak and "1 V(+squiggle)" to mean 1 Volt RMS. Correct me if this is wrong.

But if this is the case, your left-image "Units: dBV" should change to "Units: dBV(+squiggle)" because they mean dB relative to 1 Volt RMS.  This should be applied consistently everywhere "V" appears as a unit.

Also, in the list of Magnitude Units, choosing "dB" only allows setting numeric Reference values in Volts Peak.  It makes equal sense to allow a numeric Reference value in Volts RMS and that can't be done.

(I was the firmware project leader on the HP 8920A RF Test Set with multiple RF/audio generation/analysis instruments in it, similar to the Electronics Explorer board.  It had to address similar user interface issues with Volts Peak, Peak-to-Peak, Average, RMS, dB, %, dBV, dBuV, W, dBW, dBm, dBc, etc.)