Ignore until you fail E1 testing... then go redesign it and make it work. Return loss testing can be a source of headache. DON'T IGNORE the 120 ohms. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Sandor Daranyi Sent: Thursday, December 19, 2002 9:33 PM To: kaps@xxxxxxxxx Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Question regarding the differential impedance Kaps, Perhaps others may not agree, but personally, I wouldn't worry too much abo= ut the 120 ohms for E1/T1. Considering the wavelengths (and any practica= l trace lengths you are likely to have) at those low frequencies, my main= consideration about the trace width would be mostly to do with the desig= n of the protection circuit. Of course, it still makes sense to keep the= traces belonging to the same pair close to each other. Regards, Sandor PS: ...and here comes the storm of out-of-office messages! ---------------------------------------------- Sandor Daranyi Senior Design Engineer Aristocrat Technologies > I have a general question regarding the differential=20 > impedance of traces which dont have any plane above or=20 > beneath them at all. >=20 > Lets say it is 20 layer board and I am routing 100ohm=20 > differential pair on any of the layer but there is absolutely=20 > no plane above or beneath the traces. What will be the trace=20 > width and spacing I will be using for these traces. > These are the traces for T1/E1 from the connector to the line > side of the transformer. > > Do I have to calculate that by defining all of the layers as > signal layers? > Any suggestions > > Thanx > Kaps > ------------------------------------------------------------------ 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 archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages 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 archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu