In article ,
Cecil Moore wrote:

By open stub, you mean there is no loop at the bottom of the "J"?

He means the bottom of the stub is the feedpoint, like this:

+------------------------------------------------------------
|
FP
|
+-----------------

And that looks like an unbalanced feedpoint so it should result
in common-mode currents, sorta like an off center-fed dipole.

If I recall correctly, Cebik has some discussion and modelling of such
open-sleeve J-pole designs in his "Tales and Technicals" section.
Start at http://www.cebik.com/vhf/jp1.html and go down about half-way.

The version of the "non-standard J-pole" which Cebik models is fed at
bottom center, in a dimensionally-symmetrical way. His current plot
seems to show equal currents at this feedpoint, and this would seem to
make the use of a choke or balun on the feedline somewhat less
significant than with a standard J-pole.

Cebik's model would need to be modified somewhat apply to the Arrow
open-sleeve J-pole, as the Arrow is fed at the very base of the one
element rather than halfway between the two.

Anybody care to model up the Arrow, with all three elements included,
with and without a separate wire representing the outside of the coax?

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On 13 Jun 2005 08:20:08 -0700, "Al" wrote:

With just a cursory look I see that you sell "beems" instead of
"beams"

Look a little more and you will find more typo's I am sure.

Let me tell you a little war story and see what you think.

About 20 years ago my boss, a newly minted PhD, got a job teaching a
Senior/Graduate level course on Microwave Measurements Theory and
Practice at the U of AZ. At the time the U's equipment was abysmal so
he got permission to bring the kids into my lab at Hughes for the lab
portion of the class.

I got the job of devising the experiments, setting up the gear and
grading the lab notebooks. The kids could absolutely not see straight
when I graded their grammar. Their cry was, "This is an engineering
course, not an English course."

My reply was that they were prepping themselves for a job in industry
(actually a few of them already worked at Hughes) and I wrote memos
and reports every day, that if poorly written would reflect badly on
me.

Your web site is your place of business...fill it up with typos, bad
grammar and bogus claims and your business can suffer. On second
thought, considering your client base, maybe they'll never notice.


and a claim that corner reflectors work better on packet than
do Yagis is pure snake oil.

I think I said long Yagi's, something to do with phase distortion. I
am just going by what customers have told me that have used both.

Aha. So all I have to do is buy one of your antennas and write and
tell you how awful it works and you'll put that on your web site.


Simply modeling your super J-pole and adding a third element to
represent the transmission line would show that the line radiates like
crazy and affects the feedpoint Z.

I never said anything about a "super J-Pole" .

Sorry, a facetious remark that escaped you.

Other than maybe it is super simple.

If you simply modeled the OSJ and it showed the feed line radiates like
crazy, Maybe you didn't do it right. Maybe you need to step out into
the real world.

By the way, it has a 3rd element, makes it a dual J-Pole not just a
dual band.

No, I modeled the OSJVHF as depicted he

http://www.arrowantennas.com/inst/igif/ijmurs1.gif

You claim 150-162 MHz with 1.5:1 SWR. I modeled it as follows.

I saw the SWR vary from a low of 1.4:1 at 150 MHz to a high of almost
7:1 at 162 MHz.

Here's the file:

************************************************** *********************
EZNEC+ ver. 4.0

Created from MultiNEC 6/13/2005 11:25:41 AM

--------------- ANTENNA DESCRIPTION ---------------

Frequency = 150 MHz
Wire Loss: Aluminum (6061-T6) -- Resistivity = 4E-08 ohm-m, Rel. Perm.
= 1

--------------- WIRES ---------------

No. End 1 Coord. (in) End 2 Coord. (in)
Dia (in) Segs Insulation
Conn. X Y Z Conn. X Y Z
Diel C Thk(in)
1 W4E1 0, 0, 0 W2E1 0, 0, 18
0.375 13 1 0
2 W1E2 0, 0, 18 0, 0, 54
0.375 26 1 0
3 W4E2 0, 5, 0 0, 5, 18
0.375 13 1 0
4 W1E1 0, 0, 0 W3E1 0, 5, 0
0.375 4 1 0

Total Segments: 56

-------------- SOURCES --------------

No. Specified Pos. Actual Pos. Amplitude Phase
Type
Wire # % From E1 % From E1 Seg (V/A) (deg.)
1 1 0.00 3.85 1 1 0 SI

No loads specified

No transmission lines specified

Ground type is Free Space

************************************************** *********************

Where did I go wrong?

Reg Edwards wrote:
If you can't measure or calculate the MAGNITUDE of the effects,
stop
worrying about it.

Does RF burns on my lip count as a measurement? :-)

=============================

Not unless your yelp indicated how may watts the microphone was
radiating at the time. ;o)
---
Reg

Dave Platt wrote:

By open stub, you mean there is no loop at the bottom of the "J"?

He means the bottom of the stub is the feedpoint, like this:

+------------------------------------------------------------

FP

+-----------------

And that looks like an unbalanced feedpoint so it should result
in common-mode currents, sorta like an off center-fed dipole.

If I recall correctly, Cebik has some discussion and modelling of such
open-sleeve J-pole designs in his "Tales and Technicals" section. Start
at http://www.cebik.com/vhf/jp1.html and go down about half-way.

The version of the "non-standard J-pole" which Cebik models is fed at
bottom center, in a dimensionally-symmetrical way. His current plot
seems to show equal currents at this feedpoint, and this would seem to
make the use of a choke or balun on the feedline somewhat less
significant than with a standard J-pole.

An antenna model without a feedline will *force* equal and opposite
currents at the feedpoint - it is always fed through the perfect balun!

Add an un-choked feedline to the model (another thick wire, representing
the coax shield) at either side of the feedpoint, and see where the
current goes now. If you don't use a choke on a real-life antenna,
there's nothing to stop the current going wherever it likes.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Aha. =A0So all I have to do is buy one of your antennas and write and
tell you how awful it works and you'll put that on your web site.

Sure, or post it yourself on e-ham.net for the whole world to see.
But Please base your test on the real antenna, not a computer model.
And when your done send back the antenna and I will refund your money.
Just like it says on the web page.

73 Al Lowe N0IMW Arrow Antenna

In article ,
Ian White GM3SEK wrote:

The version of the "non-standard J-pole" which Cebik models is fed at
bottom center, in a dimensionally-symmetrical way. His current plot
seems to show equal currents at this feedpoint, and this would seem to
make the use of a choke or balun on the feedline somewhat less
significant than with a standard J-pole.

An antenna model without a feedline will *force* equal and opposite
currents at the feedpoint - it is always fed through the perfect balun!

Cebik's plot of currents in the "standard" J-pole shows unequal
currents all the way down to the bottom, and he notes this in his text
and asserts the need for a choke.

He doesn't say whether his models do or do not include a feedline.

Add an un-choked feedline to the model (another thick wire, representing
the coax shield) at either side of the feedpoint, and see where the
current goes now. If you don't use a choke on a real-life antenna,
there's nothing to stop the current going wherever it likes.

Agreed. The results are likely to be quite variable depending on the
feedline distance to the nearest ground. Seems to me that the worst
case would result from a small integral multiple of 1/2 wavelength, no?

My guess is that in most simple J-pole installations, the feedline
radiation and the resulting disturbance of the antenna's omni pattern
are probably not going to be worth worrying about too much. Nearby
buildings, trees, etc. are likely to result in larger differences
in the far-field pattern than any quirks in the antenna's own pattern.

As an alternative to using a choke on the feedline, what sort of
results might one get with a standard J-pole by using a half-wave
coaxial balun and tapping up a bit further on the elements?

An arrangement of this sort might solve two problems at once. One of
the problems I've noticed with making the usual plumber's-delight
copper J-pole for 440, is that the 50-ohm matching points are down
quite close to the bottom shorting-bar. If one makes attachment
clamps out of copper-pipe support straps (as is suggested in many of
the sets of plans I've seen), and if the J-pole is made from 1/2"
copper pipe with elbow and T fittings, it's difficult or impossible to
achieve a good match - the attachment clamps can't be slid far enough
down on the pipes to reach the match point, before they hit the elbow
fittings.

Using a coaxial 4:1 balun would allow the attachment points to be a
bit further up.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Al wrote:
And when your done send back the antenna and I will refund your money.
Just like it says on the web page.

Hey Al, if I send the antenna back to you, will you refund
my money? What will the bank do with a $00.00 refund?
Your antenna certainly works as advertised, and like the
Zepp after which it was patterned. But I don't know of any
real-world antenna that is immune to common-mode problems.
--
73, Cecil http://www.qsl.net/w5dxp


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Hey Al,

Don't let the nay-sayers in this NG bother you, and don't waste
your time arguing with them.

Some of them can't stand the thought that any antenna which differs
from their personal pet(s) might be good. Others can't grasp the
idea that when model predictions and actual results differ, it's the
results that count. Still others can't seem to understand that effects
too small to measure usually do not matter in the real world.

Your antenna is beautifully made, very reasonably priced, and
you are (apparently) making a successful small business with it.
Your customers are delighted, and refer their friends. You are
starting to attract imitators. How many of these accomplishments
can the nay-sayers claim?

Keep up the good work... the XYL and I love our three OSJs!
And they are now pretty much standard in our ARES/RACES
organization. NO complaints heard to date.

73, Ed, W6LOL

"Al" wrote in message
oups.com...
Sniped
I don't believe you can totally eliminate all current. There will always be
a small
amount.

Agreed, but it is small enough I don't think most people could see a
difference in performance if it had a choke or not.
All I am saying, to say the antenna won't work with out a choke is just
wrong.

I doubt I would change the antenna....Would make it cost more...
I'd consider a super deluxe version for a higher price, if they wanted
full 2 section decoupling...:/ And if I went that far, I'd use a dual
5/8 design to get more gain. You'd be reinventing the isopole...:/
MK

I have an "Isopole" here in the shop, it works good, maybe one of the
best
5/8 wave antennas I have ever tested. I think it could be built a
little better.
I have seen a lot of them that were broke.
But that is comparing apples to oranges
The OSJ is a simple 1/2 wave antenna that has 0 dBd gain.
No magic.
Again, I just think it is wrong to tell someone the antenna won't work
with out a choke.

73 Al Lowe N0IMW

Hey Al,

Don't let the nay-sayers in this NG bother you, and don't waste
your time arguing with them.

Some of them can't stand the thought that any antenna which differs
from their personal pet(s) might be good. =A0Others can't grasp the
idea that when model predictions and actual results differ, it's the
results that count. =A0Still others can't seem to understand that effects
too small to measure usually do not matter in the real world.

Your antenna is beautifully made, very reasonably priced, and
you are (apparently) making a successful small business with it.
Your customers are delighted, and refer their friends. =A0You are
starting to attract imitators. =A0How many of these accomplishments
can the nay-sayers claim?

Keep up the good work... the XYL and I love our three OSJs!
And they are now pretty much standard in our ARES/RACES
organization. =A0NO complaints heard to date.

Thanks, Ed, W6LOL

You are absolutely right.
There is an old saying "You can't please all the people all the time".
That's why I put the Money Back Guarantee on everything I sell.
The return rate is less than 1 in 1,000 units sold. That's good enough
for me.

That's it, I am done. Thanks for all the fun. 73 Al Lowe N0IMW

On Mon, 13 Jun 2005 18:07:13 -0000, (Dave Platt)
wrote:

In article ,
Cecil Moore wrote:

By open stub, you mean there is no loop at the bottom of the "J"?

He means the bottom of the stub is the feedpoint, like this:

+------------------------------------------------------------
|
FP
|
+-----------------

And that looks like an unbalanced feedpoint so it should result
in common-mode currents, sorta like an off center-fed dipole.

If I recall correctly, Cebik has some discussion and modelling of such
open-sleeve J-pole designs in his "Tales and Technicals" section.
Start at http://www.cebik.com/vhf/jp1.html and go down about half-way.

The version of the "non-standard J-pole" which Cebik models is fed at
bottom center, in a dimensionally-symmetrical way. His current plot
seems to show equal currents at this feedpoint, and this would seem to
make the use of a choke or balun on the feedline somewhat less
significant than with a standard J-pole.

But he says, "However, since the currents on either side of the
feedpoint are not balanced, a choke balun is mandatory to suppress
unwanted currents on the feedline."


Cebik's model would need to be modified somewhat apply to the Arrow
open-sleeve J-pole, as the Arrow is fed at the very base of the one
element rather than halfway between the two.

That's how I modeled it, although it makes very little difference in
the results.


Anybody care to model up the Arrow, with all three elements included,
with and without a separate wire representing the outside of the coax?

Done, before you asked.[g]