[time-nuts] Help - Hope?
rexa at sonic.net
Mon Jan 2 07:53:29 EST 2006
Sorry for top posting, but I'm shifting the original topic, and
apologies for a long semi-off topic post.
I found the original post great and respect both of you guys very much.
Tonight, (perhaps some spirits, in the holiday spirit, are influencing
me, but) I thought about this discussion in a general case.
I learned from smart people and was stimulated to know that I could hang
out with people smarter than me.
I find this conversation a great example of the best use of the
internet. John has done much work in many realms, and has shared a good
amount of his very useful creations and experience with the rest of the
world on the internet.
Magnus, I know less about but he, seems to be one of the people I would
go to for guidance on any number of subjects.
This medium has brought these two, geographically widely separate (I
assume), people together on this conversation that will probably benefit
many with John's software.
I applaud you both for your willingness to share your knowledge and many
of the products of that knowledge.
But tonight, I'm thinking about the state of the world, in general.
This is a private, and limited mailing list, but its members seem to
reflect what I see on public newsgroups. The majority of contributions
seem to be by older people. John is young by most of these standards.
Popular folklore says that the internet is populated with young people.
So my question:
Are the younger people no longer attracted to the basic questions of
science and engineering, or am I just missing the messages from young
people for some reason?
I know this mailing list is not typical, but I don't see younger people
anywhere I go to share knowledge. Wish they were there.
On Mon, 02 Jan 2006 11:42:53 +0100 (CET), Magnus Danielson
<cfmd at bredband.net> wrote:
>From: "John Miles" <jmiles at pop.net>
>Subject: Re: [time-nuts] Help w/integration problem
>Date: Mon, 2 Jan 2006 01:44:33 -0800
>Message-ID: <PKEGJHPHLLBACEOICCBJEEOEGBAA.jmiles at pop.net>
>> Thanks; yes, I've got the sqrt() part already, from both my original source
>> who requested the feature, and the Zarlink app note.
>I didn't bother to look at the Zarlink app note. Until now.
>> Naturally, the two sources don't agree. Equation 13 (and others) in the
>> Maxim app note at http://pdfserv.maxim-ic.com/en/an/AN3359.pdf says, in
>> RMS = sqrt(sum * 2)
>Yes, the magic happends between (11) and (12). The integration is 0 to infinity
>and not -infinity to infinity, since we already know it mirrors arround 0.
>Mind you that these are twice the power, not twice the amplitude. The energy at
>fc-f will have the same energy and be coherent to the energy at fc+f, so these
>energies add up perfectly. There is a special-case when you can't argue like
>this, but we can look the other way here and pick out the real reference
>literature when we need to.
>> On page 7 of the Zarlink app note, the x2 factor is left outside the radical
>> RMS = sqrt(sum) * 2
>Looks like sloppy work to me compared to the Maxim paper, which gives
>motivation to the formulas.
>> Unlike the question of whether to interpolate the column midpoints in dBc
>> space or linear spectral-density space, the position of that x2 term makes a
>> big difference in the final result. Any insights into who's got THAT one
>I hope you've got some insight on that. I could dig deeper into the issue if
>you are not quite satisfied. I have better references than the two PDFs you
>mentioned. The whole single-sides/double-side spectra issue is a bit confusing
>and painstaking at first, I know.
>> -- john, KE5FX
[snip first message]
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