JIMMIE wrote in
:

....
The evaluation of this antenna should start with connecting a choke
type BALUN at the input to isolate feedline radiation. A few feet of

Then it is not the same antenna as described.

I agree with your implication that an antenna of this type warrants an
attempt to minimise common mode current on the feedline... but that is
not a part of the design as described.

I have not said anywhere that this antenna doesn't 'work' or does 'work'
whatever that means, just commented on their opinion that it defies
conventional explanation.

They haven't suggested that the problem is their own limitation in
modelling or explaining, so it is reasonable to assume that their
implication is that it just cannot be explained in conventional terms and
using accepted tools.

I have questioned that assertion, I think it is not all that difficult to
model. It presents no more challenges than dealt with in my models of a
Bazooka (http://www.vk1od.net/DoubleBazooka/index.htm)and G5RV
(http://www.vk1od.net/G5RV/index.htm) assuming an ideal balun.

I know the ideal balun condition appears inconsistent with my first par,
the problem is that including the feedline common mode path in the model
is complicated by the huge variability from one installation to another,
both the length and route. (It is possible to model the antenna with a
specific common mode configuration... it is just that is has limited
applicability.)

I am tempted to do it one day. Although it isn't the same antenna in that
it has a balun, it is revealing. My gut feed is that the antenna with
balun is probably not that band on at lease many of the HF bands... more
if you ditch the coax section and use open wire feeder to a balanced
ATU... but we are moving further from the original.

Having said that, I do think the published VSWR figures at 145.3MHz are
fanciful and highlight your average ham's obsession with VSWR, as if that
single metric was a good indicator of system performance.

Owen

On Sep 30, 4:37*pm, Owen Duffy wrote:
JIMMIE wrote :

...

The evaluation of this antenna should start with connecting a choke
type BALUN at the input to isolate feedline radiation. A few feet of

Then it is not the same antenna as described.

I agree with your implication that an antenna of this type warrants an
attempt to minimise common mode current on the feedline... but that is
not a part of the design as described.

I have not said anywhere that this antenna doesn't 'work' or does 'work'
whatever that means, just commented on their opinion that it defies
conventional explanation.

They haven't suggested that the problem is their own limitation in
modelling or explaining, so it is reasonable to assume that their
implication is that it just cannot be explained in conventional terms and
using accepted tools.

I have questioned that assertion, I think it is not all that difficult to
model. It presents no more challenges than dealt with in my models of a
Bazooka (http://www.vk1od.net/DoubleBazooka/index.htm)andG5RV
(http://www.vk1od.net/G5RV/index.htm) assuming an ideal balun.

I know the ideal balun condition appears inconsistent with my first par,
the problem is that including the feedline common mode path in the model
is complicated by the huge variability from one installation to another,
both the length and route. (It is possible to model the antenna with a
specific common mode configuration... it is just that is has limited
applicability.)

I am tempted to do it one day. Although it isn't the same antenna in that
it has a balun, it is revealing. My gut feed is that the antenna with
balun is probably not that band on at lease many of the HF bands... more
if you ditch the coax section and use open wire feeder to a balanced
ATU... but we are moving further from the original.

Having said that, I do think the published VSWR figures at 145.3MHz are
fanciful and highlight your average ham's obsession with VSWR, as if that
single metric was a good indicator of system performance.

Owen

With enough RG58 any antenna's VSWR looks pretty good.

Jimmie

JIMMIE wrote:
With enough RG58 any antenna's VSWR looks pretty good.

With 200' of RG58 at 460 MHz, one doesn't even need
an antenna. :-)
--
73, Cecil http://www.w5dxp.com
"According to the general theory of relativity,
space without ether is unthinkable." Albert Einstein

"JIMMIE" wrote in message
...

snip

A few feet of wire draped across some tree limbs
can let you talk to the world.

Yes, absolutely!

I've told this story here before ...

My first HF antenna was a 10m vertical dipole I made out of copper water
pipes. Using a tuner, I could work 15m with it, but not 20 -- it needed more
metal. So, I grabbed an alligator clip lead and electrically added an old
8-foot ladder that was literally laying on the ground next to the dipole.
This enabled me to get a good SWR and I immediately worked Hawaii from here
near San Diego.

One wag asked if I was feeding it with ladder line. No.

On Sep 30, 4:37*pm, Owen Duffy wrote:
JIMMIE wrote :

...

The evaluation of this antenna should start with connecting a choke
type BALUN at the input to isolate feedline radiation. A few feet of

Then it is not the same antenna as described.

I agree with your implication that an antenna of this type warrants an
attempt to minimise common mode current on the feedline... but that is
not a part of the design as described.

Any additional feedline is also not part of the antenna as described
but I am sure this attributes to many of the glowing reports that
seems to
refute antenna NEC analysis.

Jimmie

JIMMIE wrote:


Any additional feedline is also not part of the antenna as described
but I am sure this attributes to many of the glowing reports that
seems to
refute antenna NEC analysis.

Jimmie

Is that why NEC can't evaluate these antennas correctly?:

http://assemblywizard.fr33webhost.co...ristics%20.pdf

Regards,
JS

JIMMIE wrote in
:

On Sep 30, 4:37*pm, Owen Duffy wrote:
....
I agree with your implication that an antenna of this type warrants
an attempt to minimise common mode current on the feedline... but
that is not a part of the design as described.

Any additional feedline is also not part of the antenna as described
but I am sure this attributes to many of the glowing reports that
seems to
refute antenna NEC analysis.

If that is to imply that common mode current only exists on the dipole side
of the common mode choke, it is a mistaken analysis. A common mistake, but
wrong nonetheless.

Owen

John Smith wrote:
Michael Coslo wrote:


Let's not forget the possibility that they didn't know how to model
the thing. I'm no great shakes at modeling, and that antenna is beyond
my prowess at the present.

Of course, I'm mpore likely to assume that discrepancies between
computer world and reality are my fault. Some others might assume that
the data they input was correct, so it must be the programs fault....

And some on the fringe might say the antenna CAN't work - the computer
says it can't!

- 73 de Mike N3LI -

Absolutely, I am NOT making any statement "they" are correct (I have
never tried this antenna myself--either as a model or as an actual
antenna in reality.)

But, anyway you cut it, and on the ground floor, there ARE discrepancies
in the basic equations, formulas and assumptions being put to use in the
NEC, someday these will be fleshed out ...

Regards,
JS

I doubt that any antenna an amateur is likely to build has some physics
not adequately modeled by the math in NEC. Exactly what might be these
discrepancies in equations, formulae and assumptions? Considering that
NEC has had decades of validation against actual measurements and a lot
of really, really smart people looking at how it works, I'd be kind of
surprised.

However, I can also easily believe that an amateur (or professional)
could build an antenna that has measured performance different than
expected from their NEC model of that antenna. The differences would
lie, most likely, in these areas:
1) Inaccuracies in the model itself. Things like earth properties (NEC
assumes uniform dielectric, it isn't) are an important source of error
for antennas close to the ground. Most amateur models do not include a
very good model of the surroundings (supports, trees, feedlines, etc.)

2) Inaccuracies in the measurements or not measuring the right things. A
good example is using NEC to get feedpoint characteristics, then
measuring at the rig, and not properly accounting for the transmission
line, particularly if the feedpoint Z is reactive.

In the professional antenna world, if someone models an antenna, then
builds it and tests it on the range, and the measurements differ from
what the model predicted, the usual assumption is that what was built
differed from what was modeled, or the measurements were off.

Jim Lux wrote:
John Smith wrote:
[A bunch of chit Jim, obviously, will/and does differ with]
Regards,
JS



I doubt that any antenna an amateur is likely to build has some physics
not adequately modeled by the math in NEC. Exactly what might be these
discrepancies in equations, formulae and assumptions? Considering that
NEC has had decades of validation against actual measurements and a lot
of really, really smart people looking at how it works, I'd be kind of
surprised.

I don't believe the above it correct. Indeed, if you will only review
my past objections and reflections on how "the NEC engine" demonstrates
"differences" you will be focused at the "focal point" of my "inquiries" ...


However, I can also easily believe that an amateur (or professional)
could build an antenna that has measured performance different than
expected from their NEC model of that antenna. The differences would
lie, most likely, in these areas:

Look, the dipole, standard monopole (1/4, 1/2, longwire, etc.) is NOT in
debate. Indeed, it is like NEC was designed to "explain/model" these, DUH!

1) Inaccuracies in the model itself. Things like earth properties (NEC
assumes uniform dielectric, it isn't) are an important source of error
for antennas close to the ground. Most amateur models do not include a
very good model of the surroundings (supports, trees, feedlines, etc.)

2) Inaccuracies in the measurements or not measuring the right things. A
good example is using NEC to get feedpoint characteristics, then
measuring at the rig, and not properly accounting for the transmission
line, particularly if the feedpoint Z is reactive.

In the professional antenna world, if someone models an antenna, then
builds it and tests it on the range, and the measurements differ from
what the model predicted, the usual assumption is that what was built
differed from what was modeled, or the measurements were off.

I could pick apart the above, attempt to poke fun, etc. -- however, I
would much rather join forces and attempt to focus on the points which
would lead us to real answers -- i.e., the arrl and illiterates have
already done enough damage, let us pursue a more productive path?

Leave us leave our minds open, OK?

Regards,
JS

John Smith wrote:

...
Leave us leave our minds open, OK?

Regards,
JS


And damn, and DAMN, and well DAMN ...

If you want to build something from a 19?? to 1950 (or beyond?)
publications, do I stop you? Is this what "you have you back up your
ego about?" It this what threatens you? If so, go ahead, go to your
grave with your pursuits, without my critique! ...

I am here about what "I AM", about "WHAT I THINK", about "WHAT I SEE",
about "WHAT I SUSPECT", about "WHAT I WONDER", about "MY QUESTIONS TO
OTHER MEN/WOMEN", about what I simply want to think about and want
answers to ... yanno, I think you are really endangerd by those "others"
here, I find ... Cecil, where are you? evil grin

If you can't participate, if you think I am am an idiot, if you think I
am a moron ... could you do it politely until I give you reason to do
differently ... indeed, I may feel threaten my "moronic brains" and
respond ... please don't take insult, just reassure me I am not wrong ...

Regards,
JS