On Apr 15, 5:11*pm, Cecil Moore wrote:
Jim Kelley wrote:
So why do you have to go to all that trouble when you want to measure
traveling wave current, but not when you want to measure traveling wave
energy?

When one measures traveling wave energy, one
is measuring an average calculated scalar value
usually forward power minus reflected power or
RMS V*I in a dummy load resistor.

When one is measuring delay, one is measuring
instantaneous traveling wave phase in real time.
Trigger on the zero crossing of the input signal
and measure the delay until the output signal
crosses zero.

That delay measurement doesn't work for standing-
wave current because the zero-crossing on the
input and output occur virtually simultaneously,
i.e. there is no relative phase shift between
input and output or between any two points on a
1/4WL wire monopole.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Cecil
I don't understand what all this sniping is all about but it does
bring up a question from me that you may be able to shed some light
upon.
I modeled a helix antenna and because of this thread I went back to
look at the phasing aspect that I had not paid atention to before now.
The phase change goes from 86 degrees upto 106 degrees. It then
abruptly chamges
to -106 degress and slowly returnes to -086 degrees and then turns
about again to 86 degrees again e.t.c.
Does this have a relationship to slow wave? What is your take on my
modeling?
Many thanks for what time you may give to this
Best rergards
Art

Art Unwin wrote:
It (the phase) then abruptly chamges ...
Many thanks for what time you may give to this

Standing wave current creates some strange
illusions like zero current points accompanied
by an abrupt large phase shift on each side
of the current node. If you deal with the
underlying traveling waves instead of the total
component wave, things become a lot clearer.

The abrupt phase change happens every so often
in a standing wave antenna. It is presented for
an EDZ in graph form on page 465, Figure 14-4 of
"Antennas" by Kraus, 3rd edition available for
a few bucks at:

http://www.abebooks.com/servlet/Sear...nnas&x=55&y=10
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com