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Old April 22nd 09, 07:18 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Dec 2007
Posts: 35
Default Electrical lenght vs. phisical lenght


"Cecil Moore" ha scritto nel messaggio
...

A 1/4WL monopole is half of an antenna. The ground plane
is the other half. The feedpoint is at a current maximum
point which is a magnetic field maximum. The high intensity
magnetic field directly encountering the earth is a lossy
condition.

A 1/2WL monopole is a complete resonant antenna. The
feedpoint is at a voltage maximum point which is an
electric field maximum. A pure electric field encountering
earth ground is less lossy than a pure magnetic field
encountering earth ground. Since the feedpoint impedance
is very high, some hams simply use a ground rod for a
counterpoise.


First thanks for replies abt the 5/4 WL monopole, i'm trying right now to
use eznec and simulate what you saw me.
One more newbie question: 1/4 WL and 1/2 WL monopoles are both end feeded.
So my feed point is exactly at the begin of monopole.
Assuming there is no feed line, or also a 1/2 WL feed line (if IIRC 1/2 wl
is the line lenght that preserve the phase of my RF wave from generator to
the end of the line...) what decide if i'm feeding the antenna on a current
maximum point or in a voltage maximum point ?? On a dipole, with the imagine
of the wave "superimposed" to the dipole in my mind, is quite easy for me
figure out if i'm feeding it on a current node or on a voltage peak (e.g
center feed vs. off center feed dipole). But since in both 1/4 and 1/2 wl
monopoles i'm at the *begin* of the antenna, what decide the feed point
modality (I or V) ?? The impedance i have at the specific point ??

Regards,
-.-. --.-., Cristiano, Italy.



 
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