Never mind, I think I see what's wrong... you can't integrate the dBc/Hz values directly. You have to turn them back into linear ratios, do the interval sum, and then, if you want dBc coming out, take 10*log10(sum).
-- john, KE5FX > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Behalf Of John Miles > Sent: Monday, January 02, 2006 12:00 AM > To: Discussion of precise time and frequency measurement > Subject: [time-nuts] Help w/integration problem > > > Does anyone have a piece of C (BASIC, whatever) code that turns > an array of > dBc/Hz values into integrated RMS noise? > > I'm trying to use a simple rectangular integrator to divide a log-log plot > into "bins": > > for (i=L_column; i < U_column-1; i++) > { > sum += ((value[i] - ((value[i] - value[i+1]) / 2.0)) * > (frequency[i+1] - frequency[i])); > } > > This just takes the midpoint dBc/Hz value between successive columns of a > phase-noise plot, multiplies it by the frequency step between the > columns in > question, and sums the result for all columns in the range of interest. > > The output of this process, when I feed a typical noise graph with values > around -110 dBc/Hz to it, with frequency values at the lower and upper > limits of 1000 and 10000 Hz, is around -1E+6. What I'd *like* is a value > corresponding to the "-63 dBc" value cited on pages 7 and 8 in > this Zarlink > app note: > > http://assets.zarlink.com/CA/Phase_Noise_and_Jitter_Article.pdf > > In this note, the author shows a noise curve similar to the ones > I'm working > with, and magically pulls -63 dBc out of the ether with no explanation of > the integration process that obtained it. (What does it mean, in the > author's words, to take the area "under" a phase-noise curve, anyway? > What's the bottom dBc/Hz value?) > > Being from the instant-gratification generation, I really don't want (and > won't understand) a calculus lecture. I want the 5 lines of code that do > the integration. :-) This is for the next release of my freeware GPIB > noise-measurement app, so your karma will be integrated along > with the noise > if you're able to help! > > -- john, KE5FX > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
