# [SI-LIST] Re: Propagation speed of a stripline trace in PCB

*From*: wolfgang.maichen@xxxxxxxxxxxx*To*: Mani Ganesan <signal.integrity2@xxxxxxxxx>*Date*: Fri, 3 Sep 2010 11:49:49 -0700

Mani, TDR measures the round-trip delay, i.e. the time it takes for the signal to arrive at the end of the line plus the time it takes for the reflection to travel back. In a ideal, loss-less transmission line this is thus exactly twice the propagation delay of the line. In a lossy line or when there are parastics it's only approximately a factor of 2 (because the propagation speed will depend on the frequency content of the signa, which changes due to frequency dependent losses); but in most practical cases the deviation from 2 will be smaller than your other measurement uncertainties. Wolfgang Mani Ganesan <signal.integrity2@xxxxxxxxx> Sent by: si-list-bounce@xxxxxxxxxxxxx 09/03/2010 11:27 AM To si-list@xxxxxxxxxxxxx cc Subject [SI-LIST] Propagation speed of a stripline trace in PCB Hi All can you anyone confirm me whether the propagation speed of a stripline trace in PCB is correct? propagation speed (stripline) = 11.8/sqrt(epslon_r) inches/ns epslon_r = relative dielectric permittivity. So for my rogers 4350 material i am having DK = 3.66 speed = 6.16 in/ns my trace length os 2.47 inches. so the signla propogation time = 400 ps. But my TDR measurement data both simulated and measured is showing around 800 pico seconds. Please see the attached plot. Can anyone let me know what is the reason on that. Thank You SI ------------------------------------------------------------------ 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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: http://www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu

**References**:**[SI-LIST] Propagation speed of a stripline trace in PCB***From:*Mani Ganesan

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