[SI-LIST] ZERO is tricksy -- Re: Re: characteristic impedance at DC
- From: Kevin Rhoads <kevin.g.rhoads@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 09 Apr 2012 22:02:21 -0400
On 4/9/2012 9:15 PM, steve weir wrote:
> Zero is still nothing,
OK, I feel I must comment on this.
Eveyone "knows" that infinity is a hard concept, a tricky concept. But
zero is really just a problematic. Just think, zero resistance is
infinite conductance.
Now regarding the "> Is TEM mode a propagating wavefront? Does it have a
cutoff frequency?" In most systems TEM has no cutoff frequency, it is
valid up to "infinite" frequency and down to "zero" frequency.
The key there is the "to" -- that is not "at" -- TEM does not mean
bupkis at zero frequency any more than it does at infinite frequency.
You can have a propagating TEM mode at any non-zero finite frequency --
that is up to infinity and down to zero BUT NOT INCLUDING those end points.
Of course, if you want to look at propagating TEM at low frequencies,
you will need large structures. Say something on the order of 3000
miles at 60 Hz, just as a for-example, for parallel wire lines with air
dielectric so v-prop on the line is close to c ...
When you push a concept past the usual limits too hard, you will end up
at some place non-sensical eventually. DC is not AC at a really low
frequency, DC is ZERO frequency, and ZERO is just as problematic as
infinity.
(My S.B. is in theoretical math, I only went EE in grad school. If
anyone wants *rigorous* discussion of this stuff, e-mail me off list.)
------------------------------------------------------------------
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 forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
- » [SI-LIST] ZERO is tricksy -- Re: Re: characteristic impedance at DC - Kevin Rhoads
