# [SI-LIST] Re: characteristic impedance at DC

• From: "Beal, Weston" <Weston_Beal@xxxxxxxxxx>
• To: "haaeri@xxxxxxxxx" <haaeri@xxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
• Date: Mon, 9 Apr 2012 22:49:59 +0000

```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,

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