On Mon, 29 Nov 2004 12:57:16 -0800, Roy Lewallen
wrote:

|I offer a third third response.
|
|On p. 175, Chipman states:
|
|"Equation (8.27) demonstrates explicitly that the shape of a standing
|wave pattern representing |V(d)| as a function of d on a transmission
|line is in no way affected by the quantities Vs, Zs and [rho]s at the
|source."
|
|And equation 8.29 on p. 176, the calculation of reflection coefficient,
|contains no source-dependent terms. I'm sure that somewhere in the book,
|the author derives SWR in terms of reflection coefficient.
|
|These are the facts:
|
|1. The SWR, positions of the standing waves, reflection coefficient seen
|looking into the line, impedance seen looking into the line, and dB line
|loss are independent of source impedance.
|2. The actual amount of power delivered to a line for a given Thevenin
|source voltage will, of course, depend on the source impedance, just as
|it would if the source were directly connected to a load. Therefore, the
|absolute amount of power dissipated in the load depends on source
|impedance. The dB line loss, however, doesn't. Also, the length of time
|the line requires to reach equilibrium after initially turning on the
|source depends on the source impedance.
|
|These can be found, explicitly stated and/or in easily interpreted
|equation form, in a host of references.
|
|I see nothing in the text Wes has kindly posted which contradicts these
|facts, and I'm sure there's nothing elsewhere in the text that does.
|
|I often have a hard time understanding Richard's postings, so it's
|possible that he's not disagreeing with the statements I've made,
|either. If so, I apologize for the misinterpretation.

In an earlier post to this thread, Richard stated:

|"This is yet another of my references that attend to my recent, short
|thread on the nature of power determination error, and mismatched
|loads AND sources. In fact ALL of these references I've offered
|explicitly describe that the source MUST be matched for ANY of these
|equations about transmission lines bandied about to accurately offer
|true answers. The naive presumptions that Source Z is immaterial to
|the outcome of analysis is quite widespread here."

I almost demurred, much as Roy did, because this statement is not
universal, but I held off because I believe (and hope) that Richard is
talking only about *power* measurement errors.

Wes