RadioBanter - View Single Post - Current in antenna loading coils controversy

November 3rd 03, 06:52 PM

On 03 Nov 2003 15:46:01 GMT, oSaddam (Yuri Blanarovich)
wrote:

You are right. It wasn't you, it was and credit belongs to Richard Clark,
KB7QHC.

Hi Yuri,

The observation was hardly original and I thought it answered the same
question that launched this current thread (in other words, your
complaint of the shortfall of modeling was already acknowledged with a
work-around offered).

What I do not see is any follow-through for that same suggestion. The
complaint has been offered twice, but the resolution abandoned as
though it had never been made.

I've visited your page, and in an effort to wean out the details (you
don't go to much effort to offer an unadorned, plain, vanilla
specification for the radiator). I had to guess about the coil length
(judging from its only metric being 2.5" diameter) and inductance (you
dismiss the importance of its Q and wholly leave this metric blank).
Tom cites a 300µH inductor, but if we are to believe he's unreliable,
then why are there no better sources of this fundamental information?
Using that same metric (coil diameter) I guess the vertical element
was 3/8" (but one picture clearly shows a thin whip which makes
charges of mismodeling a sure prospect regardless of honest effort).
60 radials are suggested, but no mention of length (if my attempts to
model it yield answers that don't fit your numbers - is it my fault?).

So I proceed with any number of presumptions and with every prospect
of charges of cooking results - this is the same odds offered in
prospecting eh/cfa claims.

OK, the plain vanilla radiator 93" tall (3/8" stock) in 93 segments
surrounded by 60 X 93" radials (#12 wire) ALL elevated 6" above a
real, medium ground.
SRC DATA @ 7.1MHz = 0.7995 - J 810.9 ohms
Current varies from 1A at drive point to 0 at tip

The adornment consists of this underspecified coil being decimated and
spread across 10 inches of space in the middle of the radiator with
lumped values of 30µH each. For the life of me, I don't know what
this exercise was to prove given the results:
SRC DATA @ 7.1MHz = 1.258 - J 1561 ohms
Current varies from 1A at the drive point to 0 at the tip
One variation on the first pass design is that when this current hits
the decimated inductor, the current drops to 0 a few inches before the
first inductor section and quickly develops an 180° shift over those
next few inches which persists on out to the tip. At the bottom of
the coil sections, the current again picks up to roughly 100mA
climbing to roughly 150mA at the top and then declining over the
remaining length of radiator. It would seem that anyone could craft
any assortment of conditions to support any of a dozen new theories
from this kind of legerdemain.

As far as I am concerned, these are merely a list of facts based upon
a poor specification supporting an argument that suffers from an
indistinct agenda apart from its lengthy round of 't'ain't so-isms.
Yuri, I still see no effort from you to fill in the current
distribution readings apart from a rather thin data-set of the two
points offered. Your call of warning was already answered some time
ago. Does the current vary across the inductor by this offered
method: yes! and in spades. Does it vary as you describe it? No, but
simple heat can explain that.

73's
Richard Clark, KB7QHC