[SI-LIST] Re: characteristic impedance at DC

Zero is still nothing, even for very large values of zero. To propagate 
you need a non-zero rate of change in the fields.

Steve.
On 4/9/2012 4:11 PM, mohammad haaeri wrote:
> Hi Todd,
> Is TEM mode a propagating wavefront? Does it have a cutoff frequency? How
> much is the characteristic impedance for a TEM mode propagating wavefront
> at 1Hz?
>
>
>
>
> On Mon, Apr 9, 2012 at 3:53 PM, Todd Westerhoff<twesterh@xxxxxxxxxx>  wrote:
>
>> 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!03176
>>
>> 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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