OK, maybe no one has measured or found usefulness of characteristic impedance at low frequencies, but people are simulating and that info (or L,R,C,G) are necessary (we are not simulating a lumped circuit or a narrow band signal. It's a wide-band signal from zero to ... and all info are necessary). Formula and many are saying infinity, but some people (and the paper I mentioned) saying not infinity. Which one is correct and why? On Mon, Apr 9, 2012 at 4:45 PM, Nick Luther <Nick.Luther@xxxxxxxxxx> wrote: > Aha! Now we are zeroing in on the question! Just to be clear, the TDR is > making an AC measurement. The TDR pulse has an edge and the rise time of > that edge is related to its bandwidth.**** > > ** ** > > I assume the authors are claiming that they can make better low frequency > Z0 measurements by TDR than they can with a VNA or frequency domain > technique and are claiming the usefulness of that information, and you?re > looking to discuss how the information would be useful. I haven?t read the > paper.**** > > ** ** > > If that?s the true scope of our discussion, I don?t have an example when > I?ve been concerned with the characteristic impedance of a transmission > line at a very low frequency. The reason I can cite is that at very low > frequencies the transmission line I?m working with is always electrically > very short, so transmission line effects are negligible, and the > characteristic impedance isn?t really seen on either side of the channel.* > *** > > ** ** > > -Nick**** > > ** ** > > ** ** > > *From:* mohammad haaeri [mailto:haaeri@xxxxxxxxx] > *Sent:* Monday, April 09, 2012 6:27 PM > *To:* Nick Luther > *Cc:* Weston_Beal@xxxxxxxxxx; si-list@xxxxxxxxxxxxx > *Subject:* Re: [SI-LIST] Re: characteristic impedance at DC**** > > ** ** > > Thanks Nick,**** > > ** ** > > I understand characteristic impedance and its usefulness at AC (not DC). > What about very low AC frequencies?**** > > ** ** > > Also, I'm reading a paper in DesignCon 2006 "Implementation of Broadband > transmission line models with accurate low-frequency response for high > speed system simulations" and they are calculating characteristic impedance > at low frequencies with TDR which is not very high or infinity as the > formula) says and not DC resistance as Weston and Todd are saying! You can > read the paper **** > > ** ** > > ** ** > > On Mon, Apr 9, 2012 at 4:16 PM, Nick Luther <Nick.Luther@xxxxxxxxxx> > wrote:**** > > One quick clarification: > > Looking at the two terminals at the input to a transmission line > (consider a center conductor and shield in a coax cable), and with > nothing at the other end (open), you likely will see an open circuit at > DC, just like the "infinite" impedance that Mohammad predicted using his > general equation. So, in a strict sense, Mohammad was correct. I want > to point out to Mohammad that he is using the equation correctly, and > this is how he should be interpreting the result that he calculated. > > The characteristic impedance is what an AC source would effectively see > at those same two terminals. > > Weston and Todd's replies explain why the characteristic impedance > calculation at DC isn't useful. Mohammad: I hope that Weston and > Todd's replies help you understand this concept. The Wikipedia link > should be very useful. I think you'll find a lot of additional > literature with a Google search. > > Nick > > -- > Nick Luther, P.E. > Design Engineer > Plexus Engineering Solutions > Ship To: 55 Jewelers Park Drive > Mail To: PO Box 677 > Neenah, Wisconsin 54957-0677 USA > http://www.plexus.com/**** > > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]** > ** > > On Behalf Of Beal, Weston > Sent: Monday, April 09, 2012 5:50 PM > To: haaeri@xxxxxxxxx; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: characteristic impedance at DC > > Characteristic impedance applies to propagating EM waves, so it does not > apply to DC. > > Or, if you look at the general equation that you cited, you can see that > when jw = 0, the impedance approaches the line resistance. Somewhere in > college I remember seeing a graph of the general impedance equation > compared to actual measurement at low frequency. They are the same above > some kHz, but diverge as frequency decreases. > > Weston > > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of mohammad haaeri > Sent: Monday, April 09, 2012 3:31 PM > To: si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] characteristic impedance at DC > > Hi, > What is the characteristic impedance of a transmission line at DC? If > you are saying Z0=sqrt(Rdc/Gdc) at DC, since Gdc=0, and Rdc is not zero, > therefore Z0 is infinite. Is it correct? > > How does behavior of L, R, G, and C (line parameters) change vs. > frequency (at low and DC, and at very high frequency)? > > Can Z0=sqrt(R+jwl/G+jwc) be used for all frequencies? > > Thanks, > mohammad > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > **** > > ** ** > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu