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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Scott,<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><span lang=EN-US>Maybe I should have used the symbol ‘
^’ instead of ‘*’ in the formula I posted yesterday, to make
it understandable for you. This equation needs no logarithmic dimension. I
would recommend the usage of this equation and all further discussion is superfluously.
<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal>73, Helmut, DC6NY<o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>Von:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Hpsdr
[mailto:hpsdr-bounces@lists.openhpsdr.org] <b>Im Auftrag von </b>Scott Traurig<br>
<b>Gesendet:</b> Donnerstag, 24. </span><span lang=EN-US style='font-size:10.0pt;
font-family:"Tahoma","sans-serif"'>November 2016 15:44<br>
<b>An:</b> Warren C. Pratt; john eckert<br>
<b>Cc:</b> OpenHPSDR<br>
<b>Betreff:</b> Re: [hpsdr] Level calculation error in Two Tone Test generation
routine<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal><span lang=EN-US>This is a really great thread, and I've
enjoyed reading it so far!<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal><span lang=EN-US>I had long since noticed that the two-tone
signal displayed each tone 6dB down from an equivalent total power single-tone
tune signal. This has bothered me for quite some time, for I also, like John,
believe that the two-tone signal should have each tone shown -3dB down from the
equivalent total power single tone signal. Why I never questioned this, I'm not
certain, however I suspect that I continue to be more concerned with UI and
audio processing issues than with signal processing issues, as the latter are
in generally excellent shape!<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal><span lang=EN-US>After reading this thread, it would appear
to me that you are both correct, but that the display of the two-tone power at
-6dB remains a bit of a mystery.<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal><span lang=EN-US>Warren quite correctly points out that, in
the voltage domain, a single tone has a peak-to-average ratio (PAR, or crest
factor) of 3dBVoltage, and the two-tone signal a PAR of 6dBVoltage. The
conversion to decibel units in the voltage domain is 20log(voltage).<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal><span lang=EN-US>At the same time, John also quite correctly
points out that, in the power domain, a single tone as a PAR of 0dBPower, and
the two-tone signal a PAR of 3dBPower. The conversion to decibel units in the
power domain is 10log(power).<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal><span lang=EN-US>I am not surprised that you think more
naturally in terms of voltage, Warren, as one of your primary goals is to
obtain a particular set of voltage conditions on a DAC.<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal><span lang=EN-US>Similarly, I am not surprised that John and
I think in terms of RF output power, because, like most RF engineers, we think
more naturally in those terms. Indeed, I almost never think in dBuV, dBmV or
any other set of voltage units, only in terms of dBm (dBmW, to be more precise,
but "dBm" is the convention in the RF engineering lexicon).<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal><span lang=EN-US>So, if my understanding that both positions
are correct is correct, that the math depends on whether one is in the voltage
or power domain, there nevertheless remains a mystery: why does the two-tone signal
show each tone down 6dB from the single tone equivalent total power condition
on the transmit spectral display? My best guess now is that the transmit
spectral display (normal or DUP mode) is displaying dBVoltage. If so, this is
quite disconcerting, because spectrum analyzers universally display in units of
power, typically dBm.<o:p></o:p></span></p>
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<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
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<p class=MsoNormal>Thanks & 73,<o:p></o:p></p>
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<p class=MsoNormal><o:p> </o:p></p>
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<p class=MsoNormal>Scott/w-u-2-o<o:p></o:p></p>
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<p class=MsoNormal><o:p> </o:p></p>
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