On Fri, 29 Aug 2003 23:36:02 -0500, W5DXP
wrote:

Richard Clark wrote:

W5DXP wrote:
But: "Every time you make a measurement, you make an error." So said
my EE prof almost half a century ago. I assume it's still true. :-)

Yes.

What can I assume from the fact that you ignored the tough questions
in the rest of my posting?

Hi Cecil,

I have no idea what you can assume. You generally express it freely
anyway.

How do you measure the exact amount of
reflected power re-reflected from the source?

Dan's spreadsheet work seems like a good place to start. It is of no
particular interest to me and doesn't respond to the challenge in and
of itself. You might find an exact answer there. Simply going to the
bench would be adequate for amateurs, guessing would eclipse the
efforts of everyone else. ;-)

It should seem obvious that the power reflected at the source
interface is governed by the standard mechanics no one wishes to
impart to the source. In other words the power returning to the
source will be reflected through the same mechanics it met at the
mismatched load, with the "exact" value varying only by the reflection
coefficient of the source mismatch and the power incident upon it. As
the line presents a media of 50 Ohms, and the source presents a 100
Ohm discontinuity, the portion of power reflected is a rather trivial
computation - except for those who apparently employ "first
principles" in one direction only. Gad, I love that bit of irony!
And they do it for the sake of educating lurkers too!

Hi Ian, George, you will find this in chapter 9 from Chipman (got it
right that time George ;-). It also accounts for the increased loss
exhibited by the example of the Challenge that so baffles everyone. I
wonder what those so bench-shy would attribute that additional loss
to? Would their astrologers suggest the opposition of Mars? Hint:
the answer works at all aspects of any planets.

For those who closely follow their astrologer's advice, I once again
suggest this only matters to those interested in accuracy. With
equipment available across the counter in exchange for a credit card
charge, their purchase is not likely to suffer any issues brought to
the forum here and they can rest assured their SWR meters will work as
advertised given the likely source Z of being 50 Ohms or
insignificantly off from that value. (Many will gladly suffer 2:1
mismatch straight from the antenna connector so they can worry it at
the antenna.) Further, for inferior purchases at similar cost (how
would they know?), they will still be unaware barring some change in
the length of cabling that will have them muttering a moment or two
before they shrug it off anyway.

73's
Richard Clark, KB7QHC