John Smith wrote:

...
Regards,
JS

Now, let me see, some gurus' are about to explain why EZNEC beats this
hands down--my ears are WIDE OPEN!

JS

Roy Lewallen wrote in news:13la97elqjdp5e2
@corp.supernews.com:

Owen Duffy wrote:
. . .
The helical problem I posed is not unusual, many if not most low HF
helicals wind up with close spaced turns at the top. . .

Out of curiosity, why?

Why are they made that way, or why my interest?

My interest harks back to measurement of field strength of emissions as
part of response to the BPL threat.

I was interested in whether NEC models might lead to a good estimate of
Antenna Factor of typical commercial mobile whips (eg Hamsticks) on a
wire frame model of a vehicle.

I did create some models of centre loaded whips in on vehicles, but I
could do a pretty close estimate of them without resorting to NEC
(http://www.vk1od.net/sc/slvaf.htm).

I wound up extending that to a piecewise representation of the helical
(http://www.vk1od.net/m40/index.htm).


Owen

Owen Duffy wrote:
Roy Lewallen wrote in news:13la97elqjdp5e2
@corp.supernews.com:

Owen Duffy wrote:
. . .
The helical problem I posed is not unusual, many if not most low HF
helicals wind up with close spaced turns at the top. . .
Out of curiosity, why?

Why are they made that way, or why my interest?

Why are they made that way?

Roy Lewallen, W7EL

Richard Harrison wrote:
You can take Kraus to the bank. I don`t know what all the fuss is about.

The fuss is about some people using standing-wave current,
whose phase is virtually meaningless, to make phase
measurements and report those measurements as meaningful
"facts" thus creating new old wives' tales that amateur
radio doesn't need.
--
73, Cecil http://www.w5dxp.com

John Smith wrote:
Cecil, don't take the whole world seriously, where would be the fun?

I'm sorry, John, the difference between a duck
is serious business. :-)
--
73, Cecil http://www.w5dxp.com

Roy Lewallen wrote:
I've always regarded email as being private and confidential, and I'm
sorry to see that Cecil doesn't give it the same respect.

Roy, some time ago, you posted one of my private emails
on this newsgroup without my permission so you have not
"always regarded email as being private and confidential".
In fact, I was appalled when it happened. Now we are even.
--
73, Cecil http://www.w5dxp.com

Ian White GM3SEK wrote:
Cecil Moore wrote:
A software model that blows up when R=0 is perfectly
acceptable in the real world. It is a software bug,
not a statement on reality.

It's only your model that blows up. If your model sees lumped-component
behavior as an impossible singularity, that cannot be correct.

It was a statement about a hypothetical model, Ian.
The model that I am using does NOT blow up. The model
that W8JI used is the one that blew up.

Other people's models of antenna loading do not have this problem.

A 3 ns delay through a 2", 10 TPI, 100 T coil at 4 MHz
is not a problem?????

In practical terms, a lumped-inductance model will take you straight to
a buildable prototype.

Yes, but the person using it will not understand reality
as witnessed by the technical impossibilities asserted on
this newsgroup and elsewhere. Wouldn't you really rather
understand the physics than put blind trust in imaginary
components that do not and cannot exist in reality? Isn't
it ridiculous to use the lumped inductance in EZNEC to try
to prove that there is no delay through a coil? Isn't it
ridiculous to assert that reflected waves contain no
energy just because you can't figure out where that
reflected energy goes?
--
73, Cecil http://www.w5dxp.com

Owen Duffy wrote:
So, NEC can model your helical so long as your helical is one that NEC
can model!

A lot of useful information can be had this way. Here's
one such implementation that segment checks OK and
illustrates the ~68 degrees of phase shift through the
coil on 7.15 MHz.

http://www.w5dxp.com/coil512.EZ

... we don't know a
measured value for Tom's coil anyway or the true stand alone self
resonance.

I tried to get him to measure the self-resonant frequency
using the coil as a monopole over a ground plane. Corum's
equation says the coil has a VF of ~0.033 giving it an
effective length of ~25 feet or an electrical 1/4WL around
10 MHz.

The measured self-resonant frequency for my 75m Texas
Bugcatcher coil was around 6 MHz. It's calculated VF
was around 0.02.
--
73, Cecil http://www.w5dxp.com

"AI4QJ" wrote in message
...
I would assume if I
was as far off in what I think the topic is supposed to be, you or others
would have jumped in to tell me AND TOLD ME WHAT THE ACTUAL CONTROVERSY IS
ALL ABOUT.

Some more about it at
http://www.k3bu.us/loadingcoils.htm
besides Cecil's pages

The main argument was the current distribution along the loading coil in a
resonant quarter wave radiator. I and bunch stated that there is a drop
along the coil, W8JI and bunch argued that not, that EZNEC "proves" it
(using lumped inductance model). Nice to see W7EL coming around and
recognizing difference between modeling the coil as a solenoid and lumped
inductance.
The net result is the overall current distribution along the radiator, which
reflects efficiency and is significant when elements are employed in the
arrays of loaded antenna elements.
The rest is just digging deeper into the pesky electron behavior.
It would be interesting to get report on W7EL visit to W8JI.

Yuri, www.K3BU.us

Yuri Blanarovich wrote:
The main argument was the current distribution along the loading coil in a
resonant quarter wave radiator. I and bunch stated that there is a drop
along the coil, ...

There is not much "drop" through the coil for the
forward current and reflected current. The "drop" in
standing-wave current is caused primarily by the
superposition of the forward current and reflected
current with their phasors rotating in opposite
directions. Assume there is zero loss in the forward
and reflected currents.

At the bottom of the coil, the forward current is 1a
at 0 deg and the reflected current is 1a at 0 deg.
The total current will be 2a at 0 deg.

At the top of the coil, the forward current is 1a
at -45 deg and the reflected current is 1a at 45 deg.
The total current will be 1.414a at 0 deg.

Here are the corresponding phasor diagrams:

http://www.w5dxp.com/phasor.gif

There is no drop in either forward current or reflected
current, yet there is a "drop" in total current. Since
lossless conditions are assumed, the "drop" is caused
100% by phasing, not by losses or radiation.

If we use a loading coil at a particular point in a
1/2WL monopole, we can get a *rise in total current*
through the coil. Both examples can be seen at:

http://www.w5dxp.com/test316.GIF
--
73, Cecil http://www.w5dxp.com