Re: Current across the antenna loading coil - from scratch

Another 'speriment occured to me, for those who think the coil current
MUST be different at the two ends by the amount corresponding to the
antenna section it replaces: try making the antenna diameter large
compared with the coil diameter, say two to four times the coil
diameter, while maintaining the same lengths, and see what happens. I
suppose you'll have to adjust the inductance of the coil, but keep its
diameter and length the same. If the current at the ends of the coil
remains nominally the same as with a thin antenna, then I'll say you're
onto something. If on the other hand, the current becomes much more
similar at the two ends of the coil, that will be evidence of a
different effect--in fact the effect that I expect is actually
accounting for the difference.

Perhaps someone would like to try that in NEC2 or NEC4 and share the
results, if nobody is actually up to building the antenna and measuring
things.

Cheers,
Tom


Tom, W8JI, wrote in Message-ID:
<1144385028.313255.108730@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:
Yuri Blanarovich wrote:
W8JI and other unbelievers that antenna and loading coils can not be
expressed in electrical degrees, can find another example in ON4UN's Low
Band DXing book, 4th edition, page 9-47, Fig 9-58, showing loaded vertical
with mast being 40 deg. 59.6 ft. long, loading coil of 144 uH taking
(replacing radiator of) 40 deg and whip of 10 deg and 14.9 ft long, for
overall 90 deg electrical and quarter wave resonant system.
Soooo, to anyone outside of "equal current worshippers" it is obvious that
coil is replacing 40 deg worth of radiator and it would drop equivalent
amount of current across the coil that corresponds to the length of radiator
that coil replaces, because rest of the "straight" radiator FORCES IT TO
DO - because of standing wave and current.

That is not correct Yuri.

Anything from a pure inductance to a very poor distributed inductor
(like a linear loading or stub) can be used and all would have
different characteristics.

A pure inductance would have no current difference at each end. A good
compact inductor would have negligible current difference at each end,
only a long straight wire would act like the "missing antenna".

One way to prove the coil does not replace missing length is to simply
move the coil to a new location in a fixed height antenna. If the coil
looked like 40 degrees, it would resonate the antenna no matter where
it was installed.

73 Tom

.

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