On 12 Jun 2005 14:15:52 -0700, "Al" wrote:

Hello, Roy & the Group.

One think you may have missed, the original post was about a Arrow
Antenna J-Pole. This is an Open Stub type J-Pole, Not a Closed Stub
type like the copper pipe ones. The OSJ does not need a choke, it does
not have a problem with feedline radiation or a problem with Common
Mode Currents.

In the typical J-pole antenna, the shield connects to the long element
and the center to the stub.

I've read, in this group, it doesn't matter which side the center
connects to. That's not true?

don't know your antenna in particular,
but I would suspect this is the case and don't believe it is considered
a radiating element.

The OSJ is not a typical J-pole.

73 Al Lowe N0IMW Arrow Antenna

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

bob
k5qwg

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

bob k5qwg

No, Open Stub means the 1/4 wave element and the 3/4 wave element are
not connected.

In the typical (closed stub) J-Pole I have seen the center of the coax
connected to ether side of the antenna, seems to work equally poor
ether way.

In the case of the Open Stub J-Pole I have found that a wider bandwidth
can be obtained connecting the center to the 3/4 wave element. (about
12 MHz.)
Connecting to the 1/4 wave element, bandwidth is only about 6 MHz.
The 2 meter band is only 4 MHz. so it really don't matter too much.
Try that with the typical copper pipe J-Pole.
73 Al Lowe N0IMW

Bob Miller 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.
--
73, Cecil http://www.qsl.net/w5dxp

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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.

Not quite. Look closer - http://www.arrowantennas.com/j-pole.html
You assume it should result in common-mode currents.
And you know what happens when you Ass u me.
73 Al Lowe N0IMW

Al wrote:

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

+-----------------x-------------------------------------------
|
FP
|
+-----------------y

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

Not quite. Look closer - http://www.arrowantennas.com/j-pole.html
You assume it should result in common-mode currents.
And you know what happens when you Ass u me.

Would you agree this is a 2m Zepp? Zepps are known to have
common mode currents. We know the current at point 'x' is
not the same as the current at point 'y'.
--
73, Cecil http://www.qsl.net/w5dxp


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Not quite. Look closer - http://www.arrowantennas.com/j-pole.html
You assume it should result in common-mode currents.
And you know what happens when you Ass u me.

But....Common mode current on the feedline can't be avoided
no matter how the antenna is fed. I agree that the antenna is
quite usable without decoupling, and I've found that the 1/2 WL
ringo's usual "gamma loop" feed is also fairly good as far as that.
But there is no way to totally avoid all currents, without some form
of decoupling. If you believe you can, try some tests adding decoupling
sections. If you don't see an increase in performance, I would
be *very* surprised. In some cases, it's possible for the currents
to add, and produce a gain at low angles, but it's fairly unlikely.
Most of the time, the pattern is skewed upwards. It takes at least
two decoupling sections to fully decouple an elevated vertical.
To me, you have none, although maybe you could argue that your
feed of feeding qualifies as a first decoupling section...Lets say
you win, and this is the case...You still need one more, if you
want to be fully decoupled... If you believe you are now, I'd be
willing to bet you are deluding yourself.
Thats not to say the antenna doesn't work ok as is...I'm sure it
probably does, except the most retentive of users...I've used
loads of halfwaves with no decoupling...But those were all on 10m,
where it's not so critical. BTW...The results of adding decoupling
sections will vary from user to user, depending on their lines.
But if the antenna is totally decoupled, the amount of current will
be the appx same for any user, no matter feed length.
When I say total, I mean as much as practical. I don't believe you
can totally eliminate all current. There will always be a small
amount.
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

On 12 Jun 2005 23:39:08 -0700, wrote:

It takes at least
two decoupling sections to fully decouple an elevated vertical.

That statement is generally correct, however, if you were to use a
bead balun things change a bit. The reason being that on 2-meters the
balun is about 10" long (about 1/8-wavelength). When model correctly,
you can observe that such a balun is pretty good at choking of common
mode current without resorting to adding a second one.

It works even better on 200 MHz and 440MHz.

73,
Danny, K6MHE

Sniped
I don't believe you can totally eliminate all current. There will always b=
e 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...:/ =A0And if I went that far, I'd use a dual
5/8 design to get more gain. =A0You'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. 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