"Cecil Moore" wrote in message
. com...
Tom Ring wrote:
Cecil Moore wrote:
There seems to be an assumption by some posters here that
a mobile antenna must be electrically 90 degrees in length.
Here's a simple transmission line example to illustrate why
that is not true in the case of a loading coil used with straight
sections of antenna. In the following example, all transmission
lines are lossless. ... 73, Cecil http://www.qsl.net/w5dxp

You guys sure like to go on-and-on starting with someones "rule of thumb" or
catch phrase, taking either correct or not so correct math to prove or
disprove what you may or may not already know...or just wave your flag in
otheres faces. I guess my real point is that I see many uses of "electrical
length" and "physical length" many of which are not used correctly. If the
mental model(s) we have and are trying to use as a basis for a field of
study don't quite work well enough to be useful most all the time, then they
probably aren't correct. The best model is one that always applies when
applied appropriately and you won't know what appropriate means unless you
have a good model to base it on. I know this soulds like circular
reasonong, but that's the way it works and the best way I can descxribe it.

I think "electrical length of a conbination of components" is a poor way to
look at it and therefore a poor mental model to use. Bring in an uneeded
term called "electrical length" or looking for the "missing degrees" is
pretty much a red herring complication. I maintain that trying to fit an
"electricall length" to such a combination helps none in the understanding.

You do the math, get the correct answer and you are done. You don't need an
extra "name".

My point would be that "elecreical length" is only correctly applicable to
_A_ single length of Transmisison line. trying to force it into every
other situation is only causing confusion and I should rest my case here,
but....
We need it because there is a velocity factor and therefore, the phisical
length is no longer good enough for discussion. It is obvious that hooking
up different lengths of different characteristic impedance transmisison line
has a complex effect on what you wind up with and it is therefore
inapropriate to use that specific terminology to describe the complex
situation. I didn't check Cecil's math, but assuming he did it correctly,
this is no surprise - it is expected as a result. However, have a need to
ascribe a TOTAL "electrical length" based on individual "electrical lengths"
of a complex combination of lines is inappropriate - not helpful for real
nunderstanding.
You might be inclined, and therefore properly understood, if you talk
about the finished product in a slightly different mannor. If the phase
angle and impedance is the same as you would have gotten with some (single
hunk of) reference line, then you could say that it "appears equivalent to"
a such-and-such line with an electrical length of X degrees, but the complex
combinatin no longer has something we can rightly call an electrical length
because it is not an _it_, but a _them_...if you get my drift.

You guys are going to use up all the words for the rest of us... (:-)
73, Steve, K9DCI
asbestos shorts fresh out of the wash...