In a message dated 5/27/2005 12:39:07 P.M. Central Standard Time,
alwilliams@olywa.net writes:
Not too long ago, when I asked why reflectors of a Yagi are longer than the
driven element and directors of a Yagi are shorter than the driven element,
several Towertalkians advised me to look at the current table output. In
particular to look at the phase angle of the segments. One respondent advised
that the reason is that "....that is the way it is..."! At first I scoffed at
this response but after thinking about the difficulty of adding the current
phase angle to the time delay angle caused by the separation between elements
for all combination of segments, I decided that yes, that is the way it is.
What the computer can do in a fraction of a second is beyond what I could do.
However I "discovered" what seems very odd to me and am hoping that
Towertalkians can explain it.
I modeled a 40 meter dipole at 60' above medium ground using EZNEC with
real/high accuracy. At resonance the source impedance angle was reduced to
zero
and for frequencies above resonance the phase angle started increasing
positively (inductive). For frequencies below resonance the phase angle
started
increasing negatively (capacitive). This is in agreement with what antenna
books inform us.
But the phase angle of each segment (except the center one) always was
negative with increasing angle as the segment chosen goes to the end of the
element.
(In this case 31 segments per element). This negative phase angle was
reported for both higher and lower frequencies (equivalent to shorter and
longer
elements?).
Why do individual segments always show a capacitive phase angle while the
whole element will show either capacitive, zero, or inductive phase angle?
k7puc
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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Could it be that since the segments are so short compared a resonant length
that they, like short antennas, show up as highly capacitive?
73/K5GW
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
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