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Old May 8th 09, 12:12 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default Dual-Z0 Stubs

Jim Kelley wrote:
Ask as many times as you like. You're asking me explain how to use a
printout from a computer program to measure current. The question makes
no sense, Cecil. What I'd like to know is how is one supposed to
respond to such nonsense.


Jim, I'm sorry that you are not capable of converting
the EZNEC printout into a graph. Would you like me to
show you how to do it?

If what you want to know is how to measure current on a coil, I suggest
that you need to build a current probe. Ask W8JI about it. According
to your reference, the Corum paper, you would then plot current as a
function of position along the axis of the helix. From that one can
determine the axial length of the standing wave pattern - the length of
the wave, so to speak. Given the frequency and the wavelength, one can
easily arrive at the propagation velocity. If you need help with it,
good luck.


You're preaching to the choir, Jim. You and I know that
the phase information for a standing wave is contained
in the amplitude and the phase relative to time is constant
at all points on the antenna for any particular time.

What you should be doing is explaining that to w7el and
w8ji because they don't seem to understand that the
current phase in standing wave antennas does NOT change
with distance. Here's an earlier question that you guys
ignored. Given a 1/2WL dipole with current probes at x and y:

---------------------------fp--------x--------y---------

points x and y are 30 degrees apart. What will be the
difference between the phase of the current at x and
the phase of the current at y? EZNEC says ~1 degree.
How can current phase change by one degree in 30
degrees of wire?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
 
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