Loading Coils; was : Vincent antenna
 

"Cecil Moore" wrote in message
t...
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

Exactly and thanks for your insight into the subject.
The argument was/is about (net, resultant) current along the loading coil in
a RESONANT quarter (standing) wave monopole, aka mobile 80 m loaded whip,
which was measured by W9UCW and ridiculed by W8JI et al.
The rest is QRN.

Yuri, K3BU.us

Loading Coils; was : Vincent antenna
 

On Dec 3, 8:34 pm, Cecil Moore wrote:
....
It's your tarbaby, Tom, not mine.

Hey I'M not the one who's made well over a hundred postings in this
thread, man. Can the delusional see that they are? Have a good life;
I'll try in the future to not engage you in meaningful discussions
about your, um, tarbabies.

Loading Coils; was : Vincent antenna
 

On Tue, 04 Dec 2007 02:16:36 GMT, Gene Fuller
wrote:

The calculator is at

http://hamwaves.com/antennas/inductance.html

I believe that Owen first mentioned that website, but I could be wrong.

I am looking at the calculation for beta, the axial propagation factor.
It appears to be unchanged for any length of coil from very short to
much longer than a quarter-wave resonant length.

Hi Gene,

On visiting the site, I plugged in Tom's numbers, specifically:
D = 50mm
N = 100
l = 254mm
d = 1mm

ß varied by frequency in a non-linear fashion, roughly x10 per decade
shift up in frequency from 40kHz.

What was strange was how "Parallel stray capacitance" wandered the map
to become inductive (-1 pF) at 40 MHz (and become a non-number above).

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

On Mon, 03 Dec 2007 20:26:18 -0800, Roy Lewallen
wrote:

Both NEC and EZNEC provide simple ways of generating a helical model.

Hi Roy,

EZNEC refuses to operate with Tom's coil (wire overlaps and geometry
issues if I recall from the last failure).

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

On Mon, 3 Dec 2007 18:29:24 -0800 (PST), K7ITM wrote:

I can make the antenna conductor be the outside of a piece of
coaxial cable, and use the coaxial inside as a shorted stub which
reflects a pretty good (fairly high Q) inductive reactance back to a
particular point such as a quarter of the antenna length back from
each end, where the stub connects across a gap in the outer
conductor. Can I use such an inductive reactance to tune the
antenna? Will there then be a difference in current at each end of
the gap across which that reactance connects?

Hi Tom,

Interesting proposition. I like it.

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:

Hi Roy,

EZNEC refuses to operate with Tom's coil (wire overlaps and geometry
issues if I recall from the last failure).

Please contact me by email if you think there's EZNEC isn't doing
something as you think it should. I'll either explain why it's doing
what it does or, if there's a bug, will fix it.

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

On Tue, 04 Dec 2007 00:31:02 GMT, Cecil Moore
wrote:

I apologize, Richard, like W8JI, I am unwilling to cut my
75m Texas bugcatcher coil in half. But then, his coil didn't
cost $180 either. :-)

The experiment that you are suggesting is exactly the same
that I suggested to W8JI but he was unwilling to perform
such and I tend to understood why. :-)

As a data point, in the previous argument a couple of years
ago, W8JI tried to use the lumped inductance feature of EZNEC
to "prove" there is never any phase shift through any coil. :-)

So, the short of it (the long of it is above) is that neither of you
have valid data that demonstrates a Corum solution. I'm not
surprised.

Seeing that there is no valid conclusion, it must be by the extended
logic of your understanding of English that both your and Tom's
positions are thus INVALID.

Anything left to introduce, barring actual test results, is not
superposition, but supposition.

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote in
:

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?

I suspect that it is a technique to try to maximise the current moment to
get the highest radiation resistance. They then build out the radation
resistance with loss to achieve a specification maximum VSWR for direct
feeding at the base with 50 ohm line.

Owen

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
Richard Clark wrote:
EZNEC refuses to operate with Tom's coil (wire overlaps and geometry
issues if I recall from the last failure).

Please contact me by email if you think there's EZNEC isn't doing
something as you think it should. I'll either explain why it's doing
what it does or, if there's a bug, will fix it.

It's not a bug. Tom's coil dimensions violate
the helix segment guidelines at 4 MHz.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
So, the short of it (the long of it is above) is that neither of you
have valid data that demonstrates a Corum solution. I'm not
surprised.

In addition to my measurements on the 75m Texas
Bugcatcher coil, I also measured ~12-13 ns delay
through 50 turns of the same coil stock that Tom
was using when he measured a 3 ns delay through
a 100 turn coil. That 12-13 ns delay is within
15% of the Corum equation predictions.
--
73, Cecil http://www.w5dxp.com