**From:** S. Weir (*weirsp@atdial.net*)

**Date:** Tue Jun 05 2001 - 11:29:49 PDT

**Next message:**Doug McKean: "Re: [SI-LIST] : Shielding Effectivness Question"**Previous message:**Rob Hinz: "Re: [SI-LIST] : Shielding Effectivness Question"**In reply to:**Chris Rokusek: "RE: [SI-LIST] : Antenna Problem on the Board"**Next in thread:**RMELLISON@aol.com: "Re: [SI-LIST] : Antenna Problem on the Board"

Chris,

I would like to resolve this, and believe the comments below can.

At 10:36 AM 6/5/01 -0700, you wrote:

*>Steve,
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*>
*

*>Please see within.
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*>
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*> > Chris,
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*> >
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*> > I don't see how you can justify the surprise introduction of a 20 ohm
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*> > driver resistance into the discussion. That reduces the incident
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*> > amplitude
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*> > seen by the load at the far end similarly. Is it appropriate to
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*> > compare a
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*> > circuit that provides 70% (Rdvr=20, Zl=50, Rload=50), against one that
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*> > provides 100%, (Rdvr=20, Rser=30, Zl=50, Rload=open)?
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*>
*

*>
*

*>Sorry if this is a surprise, I used a 20 Ohm driver in my first reply to
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*>this thread to which no one posted any objections.
*

Chris, I'm sorry, but I never saw that 20 ohm driver in the discussion. I

think this is easier to analyze if we leave the driver at zero ohms for the

time being.

*> > For your analogy of a tight "U" shaped trace, I think that model is
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*> > great. But the radiating cross-sectional area does not increase. The
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*> > whole point is that we are assuming TEM, and so the wave is
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*> > polarized. The
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*> > scalar formula you are using holds only for the perpendicular
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*> > cross-section
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*> > which is just the original Length * Height. Put another way, if we have
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*> > two traces, A and B where the driver for A is on the left, and B
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*> > is on the
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*> > right, and they are close to each other, driving each line
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*> > alternately will
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*> > not increase E over what we get by driving one line alone.
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*>
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*>
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*>Doesn't look like we are going to converge on this one. I can't convince
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*>myself if I take 1/100th of the current and put it on 100 lines each firing
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*>sequentially that they are not going to add in phase at some point in the
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*>far field. Especially if I consider the extreme case where each of the
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*>lines are electrically short such that there would be complete overlap
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*>between firing times.
*

If the sources are all on the same side, I agree with you. If they are all

very close together we approximate simple vector addition.

I disagree that this is a model of the reflected wave case. See below.

*>Also, no one yet has mentioned the added discontinuity in the case of series
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*>termination whereby the wave must make a reversal? Although this is a
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*>higher frequency effect probably on the order of the oh-so-fun-trace-corner
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*>thread, it should also be noted.
*

Here, I think you are hinting yourself to the solution. The reflected wave

is not in-phase, it is another wave propagating in the opposite direction

over the same path at a later time. If you return to your scalar equation,

and we connect an oscillator for one minute or two, our E measurement will

still be the same during the on times of the oscillator.

As the reflected wave propagates back towards the source, I returns to zero

at each point as di/dt goes through its maximum negative value w/reference

to the incident wave front. We get new spectral components along the line

based on f = 1/2*(Tflight_load - Tflight_local_point ) for each point on

the line. This effects a sort of down-chirp. The energy gets dispersed

over a frequency range.

Regards,

Steve.

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**Next message:**Doug McKean: "Re: [SI-LIST] : Shielding Effectivness Question"**Previous message:**Rob Hinz: "Re: [SI-LIST] : Shielding Effectivness Question"**In reply to:**Chris Rokusek: "RE: [SI-LIST] : Antenna Problem on the Board"**Next in thread:**RMELLISON@aol.com: "Re: [SI-LIST] : Antenna Problem on the Board"

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