Keith Dysart wrote:
On Jan 2, 9:59 am, Cecil Moore wrote:


Please reference a good book on optical EM waves
for a complete answer.



It is a body of physics knowledge that has existed
since long before you were born. It should have
been covered in your Physics 201 class. That you
are apparently unaware of such is a display of
basic ignorance of the science of EM waves.



The basic theory applies specifically to coherent
waves (which are the only EM waves capable of truly
interfering). CW RF waves are close enough to ideal
coherency that the theory works well. It would no
doubt work for a coherent Fourier series as well
but I don't want to spend the time necessary
to prove that assertion.



Again, it is not *my* approach and is described in any
textbook on "Optics" including Hecht and Born & Wolf.

Well, others more knowledgeable than I in optics
have disputed whether *your* approach accurately
represents those described in the textbooks.

In any case, being applicable only to sinusoids
limits the general applicability to transmission
lines which happily work at DC.

...Keith


It is sadly amusing that Cecil takes so much comfort in optics. The
electromagnetic theory for optics (e.g. somewhere in the vicinity of
visible light) is of course identical to the electromagnetic theory for
HF. The preferred applications and shortcuts are sometimes a bit
different, but that is simply a matter of convenience and of no
importance here.

I have a couple of editions of Born and Wolf, which is a high level
reference and often considered the standard for optics. I have been
unable to find even one mention of "constructive" or "destructive"
interference in their writing. Of course they delve into the topic of
interference in excruciating detail. They don't, however, ascribe any
particular mysticism or magic to interference. It is simply what happens
when the wave fields are superposed.

The more popular accounts, such as the FSU Java applet on interference,
the Melles-Griot web site, and apparently the text by Hecht, stay a bit
further from rigorous analysis. Therefore they resort to handwaving
requirements such as destructive must be balanced by constructive, blah,
blah, blah.

Adding the voltages in the manner you and Roy have done is precisely the
same operation as Cecil's interference method, without the emotional
baggage.

73,
Gene
W4SZ