On 25 mayo, 12:51, Richard Clark wrote:
On Tue, 25 May 2010 00:45:36 -0700 (PDT), lu6etj
wrote:

To Richard: What I mean is irrelevant :) *relevant is what Walt
wanted to say in this sentence: *"Because of the absorption of the
pad, the generator sees a nearly perfect match for all load conditions
and all reflected power is lost "
Pllease, tell me what in english means "all reflected power is lost"?
I understood (or translate or interpret) that reflected power is
dissipated in the pad: Is it a bad translation/interpretation?

Hi Miguel,

Your translation is fine.

However, I have no idea what the pad design looks like, nor do I know
the component values. *I have calibrated thousands of standard pads at
frequencies up to the 12 GHz. *They came in either a Pi design, or a T
design. *Their intended use is in system isolation. *That is, they
isolate the source from the load OR isolate the load from the source
OR isolate both. *For certain component values, you can replace the
"OR" with "AND."

You would isolate the source to keep its frequency and power constant.
You would isolate the load to keep line SWR flat. *For this line
application, it is assumed you are calibrating either a load equal or
nearly equal to Zc, or you are measuring RF power. *These are the
purpose of pads (they also serve the same function in audio circuits).
Measuring power in the presence of SWR other than 1:1 requires
sophisticated math that is rarely discussed here. *Most discussion
usually accepts the presumptions of special cases (which are often
sufficient) and employ less rigorous formulas (which serve well within
the unstated presumptions).

In conventional Kirchoff analysis, the resistor that bridges the
transmission line opening becomes the source (that is Vs and Rs). *Pad
design usually makes that one resistor for the Pi pad, or two
resistors for the T pad. *If you are working in accurate and precise
measurement, you then account for the input (source) resistance in
parallel/series combinations. *This second computation is the numeric
analysis of isolation. *The higher the ratios of these pad resistors,
the higher the isolation.

It doesn't normally serve any use to have the pad apparent resistance
(what I called Rs above) different from Zc or from Zload, but as this
component is a sacrificial one, the designer may choose to put it to
use to achieve a desired goal. *Pad performance suffers with heat due
to energy combinations that come from multiple/single sources.

73's
Richard Clark, KB7QHC

Dear friends

Sincerely it was not my desire to vivify old polemics but to tell the
truth, eight years it is a lot of time for not having arrived to a
consent!; hey boys this is science non religion! We must have a way
of leaving the well! :)

Is not possible you are using different models to describe an only one
phenomenon?, as looking at the same cat from their muzzle or from his
tail believing each one his cat is the true or real "cat" :)

I finished reading Cecil's article (http://www.w5dxp.com/nointfr.htm)
and I took of his example that of the 12,5 ohm load. I took a Smith's
chart and obtained the line input impedance, then I applied basic
circuits theory and I obtained the same value of power dissipated in
Rs -exactly-
As I see, if we use a simple electric model of generators and
impedances to solve the problem (maybe like Owen suggests), we can
explain the dissipation in Rs without appealing to any reflected power
returning into the generator because the interference phenomenon that
Cecil describes takes place to form the impedance that generator
see.
Or alternatingly the dissipation can be described by means of the
equations that Cecil shows in its page. In such case we should
consider both powers (direct and reflected) operating simultaneously
on generator resistance. Same cat, different points of view... :)

Perhaps my vision is naive but this situation reminds me an example of
Sears and Semansky book "University physics" (third edition) where he
explains that energy can be thought as not transported by charges in
movement, but for the electromagnetic field associated to them. Last
is a little hard to see -Poynting vector et al- :) but it is
applicable.

Always has been a pleasure for me to read you. I have learneing very
much from your enthusiastic discussions. You made me think of things
that I never thought without your help. Thank you.

Miguel Ghezzi . LU6ETJ

PS: Meanwhile I take the Owen advice and I am still studying!