[SI-LIST] Re: Circle bus topology; Circular Firing Squad?

  • From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Mon, 30 Jul 2007 13:01:51 -0700

Great idea!  How about coloring the
electrical waves...   :-)
Arpad
====================================

________________________________

From: Vinu Arumugham [mailto:vinu@xxxxxxxxx] 
Sent: Monday, July 30, 2007 12:59 PM
To: Muranyi, Arpad
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Circle bus topology; Circular Firing Squad?


Hopefully, they can be a different color without affecting their mechanical 
properties...?

Or, one can perform a thought experiment with two water wavefronts, each of a 
different color, approaching from either end of a trench and colliding.

Thanks,
Vinu

Muranyi, Arpad wrote: 

        This discussion (argument) makes me think of an analogy.
        
        Imagine two identical balls in space approaching each other
        along the same and perfectly straight path.  At some point
        they collide with a perfectly elastic collision.  Based on
        the laws of physics they reverse their direction and begin
        to travel in the opposite direction they came.
        
        Hmmm.  Or does the ball that came from the right continue
        on the left and the one that came from the left continue
        on the right?  I can't tell, they are identical...  :-)
        
        Arpad
        
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
        
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
        =3D=3D=3D=3D=3D=3D=3D=3D=3D
        
        -----Original Message-----
        From: si-list-bounce@xxxxxxxxxxxxx 
[mailto:si-list-bounce@xxxxxxxxxxxxx] =
        On Behalf Of steve weir
        Sent: Monday, July 30, 2007 11:25 AM
        To: Vinu Arumugham
        Cc: olaney@xxxxxxxx; ron@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
        Subject: [SI-LIST] Re: Circle bus topology; Circular Firing Squad?
        
        Vinu, I disagree.  The 'even' mode, the common to reference of each=20
        waveform encounters the illusion of an open at the intersection.  The=20
        'odd' mode, ie the difference to reference between each encounters 
the=20
        illusion of a short.  While this approach yields the correct results, 
I=20
        find it more cumbersome than the real behavior which is two 
wavefronts=20
        that pass through each other as they propagate in opposite directions=20
        down the same transmission line.
        
        As previously discussed in this thread, we can take two drivers at 
the=20
        opposite end of the same line and drive them as needed to demonstrate=20
        any of the possible behaviors.
        
        Best Regards,
        
        
        Steve.
        
        Vinu Arumugham wrote:
          

                When identical wavefronts are sent through the two branches of 
the=20
                loop and meet at the far end, each wavefront can be described 
as being =
                    

        
          

                reflected by the virtual open circuit.
                When one wavefront is "marked", the wavefronts do not encounter 
a=20
                virtual open circuit. One wavefront encounters a high impedance 
and=20
                the other a low impedance compared to the line impedance. The=20
                subsequent reflections of opposite polarity can be described 
as=20
                producing the illusion of the wavefronts flowing through rather 
than=20
                being reflected at that point.
                
                In other words, it seems to me that both the reflection and=20
                reinforcement descriptions are perfectly valid and each is as 
real or=20
                illusory as the other.
                
                Thanks,
                Vinu
                
                olaney@xxxxxxxx wrote:
                    

                        There is a difference, Ron, and my experiment 
illustrates it.  It is =
                              

        that
          

                        rather than bouncing back as a relection on the same 
trace, the loop
                        return signals are the result of a round trip without 
reflection.  =
                              

        Two
          

                        open ended lines in parallel will show an impedance 
profile similar =
                              

        to
          

                        that of the loop *only* if the trace lengths are 
matched.  The fact =
                              

        that
          

                        this special case is indistinguishable from a loop at 
the driving =
                              

        point
          

                        is interesting, but does not make it equivalent in 
terms of the =
                              

        origin of
          

                        each return signal.  If you have a means to mark the 
driving signals =
                              

        so
          

                        that they can be distinguished from each other, the 
difference =
                              

        between
          

                        double open ended traces and with the ends shorted 
together can be
                        observed.  As you say, try it with a couple of pieces 
of coax and a =
                              

        TDR
          

                        if you disagree.  It'll work best if you use a separate 
series
                        termination for each trace rather than a single 
backmatch resistor =
                              

        for
          

                        both so that you can see the return signals separately. 
 I mentioned
                        ferrite but a high frequency LC trap on one leg to 
notch out a =
                              

        specific
          

                        frequency might be more convincing.  With two traces, 
the marked =
                              

        signal
          

                        returns on the same trace.  Create a loop by shorting 
the ends =
                              

        (making
          

                        sure that the short maintains the correct path 
impedance), and the =
                              

        marked
          

                        signal returns on the other trace.  With identical 
traces (or coax) =
                              

        and
          

                        identical driving signals, as you propose, the 
difference is there =
                              

        but
          

                        you can't see it.  That does not mean that the cases 
are equivalent, =
                              

        just
          

                        that your experimental setup cannot distinguish between 
them.  Hence, =
                              

        the
          

                        need to mark the signals.  Steve explained it well.  
This would make =
                              

        a
          

                        good question for the electrical engineering 
professional licensing =
                              

        exam.
          

                        Orin
                        
                        On Sat, 28 Jul 2007 23:29:35 -0700 steve weir 
<weirsi@xxxxxxxxxx> <mailto:weirsi@xxxxxxxxxx>  =
                              

        writes:
          

                         =20
                              

                                Ron, yes if the signals exactly match then 
Ron's description of the=20
                                apparent open end matches the illusion.  It is 
an illusion just the=20
                                
                                same.  This is where Orin's proposed experiment 
can provide insight. =
                                        

        
          

                                =20
                                Any difference between the two wavefronts is 
not accounted for by=20
                                the=20
                                open end model.  That odd mode if you will 
encounters the illusion=20
                                of a=20
                                dead short at the same juncture where the even 
mode Ron and you=20
                                describe=20
                                encounters the illusion of an open.  Account 
for both the even and=20
                                odd=20
                                signal modes and you will get the right answer 
from the illusion=20
                                just as=20
                                you will if you follow the formal, exact, and I 
think simpler view:=20
                                that=20
                                the two wavefronts continue to propagate until 
they are absorbed.=20
                                
                                Steve.
                                ron@xxxxxxxxxxx wrote:
                                   =20
                                        

                                        Consider for a moment a 50 ohm source 
driving two equal length 100=20
                                             =20
                                                  

                                ohm=20
                                   =20
                                        

                                        lines unterminated(open circuit)
                                        TDR will show the open circuit at the 
end of the lines just as if=20
                                             =20
                                        there were one 50 ohm open ended line.
                                        
                                        Next consider what will happen if you 
connect the open ended lines=20
                                             =20
                                        together.  No change.  It will still 
reflect back as an open.
                                        
                                        Ponder that for a little and try it 
with a couple pieces of coax=20
                                             =20
                                                  

                                and a=20
                                   =20
                                        

                                        TDR if you disagree.
                                        
                                        
                                             =20
                                                  

                                --=20
                                Steve Weir
                                Teraspeed Consulting Group LLC=20
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