On Jun 13, 10:04*pm, Owen Duffy wrote:
Richard Clark wrote :

Understanding what is available at *Walt's bench, Pf could be off by
5W or 5%. *The 0 reading also suffers the same 5W indeterminacy if it
is measured on the same scale (assuming he is using a Bird wattmeter
with a 100W slug).

Richard,

You can wax on all you like, and try as hard as you like, but if the
source was exactly Zs=50+j0, then the Bird 43 reading for Pf should be
exactly the same.

RF measurement is as you note, fraught with problems, but here is a
relatively simple case. Walt reported that he adjusted the radio on a 50
ohm load, measured Pf and Pr, then substituted another load, no other
changes and reported a 5% reduction in Pf.

I will leave you to arguing wether Walt's observed 5% reduction is of any
value.

Anyone who accepts that a competent measurement technician, competently
using the Bird 43, can reasonably discern a 5% reduction in Pf when it
should be 0% if Zs=50+j0, might question whether that observation
supports the proposition that Zs=50+j0.

Owen

Owen, I don't understand where you found a 5% drop in power when you
say it should have been 0%. A 5% drop from what value to what value?
Where did you find that data? If you're referring to 100w Pf with the
50 + j0 load and then the 95w Pf the mismatched load, you've got to
understand that the source was now delivering only 75w, and the 20w of
reflected power added to the 75w = 95w. These are two separate
measurements--the first a stand-alone value and the second the sum of
two values. Is this a point you overlooked?

Walt