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