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Re: John, you were sucker-punched, then piled on, by the Usual Suspects.

Steve, and anyone else interested, please look at Arnies graphs closely. This is a ONE stage measurement, and a very good one in general. I use a TWO stage measurement, and this gives me a technical advantage.

What advantage, John? The only difference is that you're nulling out the fundamental and applying some voltage gain. What advantage does that give you? You're not changing the ABSOLUTE values. You're just playing decbiel games.

OK folks, what is the magnitude of the 7th harmonic on Arnies second graph? Do you think that it is -125dB ? Well, that's wrong, as you have to subtract 30 db from it, because the graph does NOT start from the top

No, you don't have to substract 30dB from it. That's the nice thing about Arny's plots. You don't have to do ANYTHING to know what's going on, unlike yours where you don't seem to have the foggiest idea how just much gain is being applied AFTER the cable and BEFORE your Mac The Scope so no one can look at your plots and be able to determine EXACTLY what the ABSOLUTE values are.

Your Mac The Scope's dB scale is referenced to 1 volt, same as Arny's SpectraLAB. Arny fed the signal straight into the cable and straight from the cable back to the analyzer. You run yours through a notch filter and God knows how much voltage gain so that no one can determine ABSOLUTE values for your plots.

If your claim that one needs to add 50dB to your plots to get the proper values is true, then YOUR 7th harmonic is indeed at -113dBV and Arny's is indeed at -125dBV.

That gives -95dB for the seventh harmonic. My RS case 7th harmonic in my test is about -110 to -115db dB.

No, John. That gives -125dBV for Arny's seventh and -112dBV for your seventh.

My residual with a VDH cable is usually about 120 to -125dB.

John, if your 50dB figure is to be believed, your noise floor BOTTOMS OUT at -120dBV. So is the 50dB figure you claimed incorrect or what? Do you have the foggiest idea what you're doing?

Remember, the important thing to consider here is the 30 dB offset in Arnies measurements.

No, John. There isn't a 30dB offset in Arny's measurements. His measurements were taken straight off the end of the cable as it was being fed a 30mV signal.

What there is is a 50dB offset in YOUR measurements. That's because you're APPLYING VOLTAGE GAIN BETWEEN THE OUTPUT OF THE CABLE AND THE INPUT IF YOUR MAC THE SCOPE! But you don't seem to REALLY know EXACTLY how much gain is being applied so no one can look at your plots and know EXACTLY what the ABSOLUTE levels are.

Distortion products must be measured against the reference signal, in Arnies case, but my ST1700 does the normalization automatically, so I don't have to change my measurements to get the correct result.

And in Arny's case, the reference signal is left intact so we can all see EXACTLY what's going on. Because you're nulling out the fundamental and applying some amount of voltage gain, your plots are largely worthless because no one can know what the ABSOLUTE levels are without relying on your knowing how much voltage gain is being applied.

Here's the facts, John:

If what you say is true and one has to add 50dB to your plots to get the proper dBV levels, then Arny's noise floor is at -138dBV and yours is at -120dBV. Making Arny's noise floor 18dB lower than yours. And Arny's 7th harmonic is at -125dBV, while yours is at -112dBV. Making Arny's 7th harmonic 13dB lower than yours.

Are you just playing a smoke and mirrors decibel game here or do you simply not understand what's going on?

se




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