[SI-LIST] Re: characteristic impedance at DC
- From: "Todd Westerhoff" <twesterh@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 9 Apr 2012 18:53:39 -0400 (EDT)
Mohammad,
Characteristic Impedance (sometimes called surge impedance) is the
impedance seen by a propagating wavefront. It's been covered at length
multiple times, including this overview in Wikipedia:
http://en.wikipedia.org/wiki/Characteristic_impedance
DC impedance from a typical transmission line ranges from nil to a few
ohms, depending on the line geometry and length. It's amenable to direct
physical measurement in many cases. Here's a device that can be used to
affordably make such measurements with 4 digits of precision:
http://www.radioshack.com/product/index.jsp?productId=2103176
Hope that helps,
Todd.
Todd Westerhoff
VP, Software Products
Signal Integrity Software Inc. ? www.sisoft.com
6 Clock Tower Place ? Suite 250 ? Maynard, MA 01754
(978) 461-0449 x24 ? twesterh@xxxxxxxxxx
?I want to live like that ?
-Sidewalk Prophets
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of mohammad haaeri
Sent: Monday, April 09, 2012 6:31 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
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