Hello,

What's the upper power limit for your typical homemade VHF
J-Pole??

I made a super J-pole with 3/4" copper tubing, and it seems to
handle 350 watts very well. But i need to make something smaller, but
without giving up the power handling ability.

It might depend some on the diameter of the tubing (1/2" versus
3/4").

Any knowledgable advice greatly appreciated.


Slick

Ever thought about a 1/4 wave groundplane? Power is
limited by the type of insulator used in building it.
Then again, the same thing holds true for a 'J' pole.
'Doc

"'Doc" wrote in message ...
Ever thought about a 1/4 wave groundplane? Power is
limited by the type of insulator used in building it.
Then again, the same thing holds true for a 'J' pole.

Plumber's Delight J-pole doesn't require
an insulator at all... I'd imagine that it could
take all the power you could pour into it,
probably take way over legal limit to melt
a half-inch copper pipe J-pole.
__
Steve
KI5YG
..

Stephen Cowell wrote:

Plumber's Delight J-pole doesn't require
an insulator at all... I'd imagine that it could
take all the power you could pour into it,
probably take way over legal limit to melt
a half-inch copper pipe J-pole.
__
Steve
KI5YG
.

None at all? Are you real sure about that?
Think about it...
'Doc

"'Doc" wrote in message ...


Stephen Cowell wrote:

Plumber's Delight J-pole doesn't require
an insulator at all... I'd imagine that it could
take all the power you could pour into it,
probably take way over legal limit to melt
a half-inch copper pipe J-pole.
__
Steve
KI5YG
.

None at all? Are you real sure about that?
Think about it...
'Doc


Yeah, no insulators at all... using plumber's delight.

The bottom of the J is strapped together. The feed point is then moved up
from the bottom along the 1/4 wave matching section until a match is
obtained.

This approach can be pretty nice. I used three sections of steel mast for a
30 feet tall pipe, grounded at the bottom for lightning protection. I then
added a 1/4 wave piece of conduit 3/4 wave down from the top strapped with
sheet steel. Made a 1/2 wave balun from coax and found the lowest SWR feed
point along the matching section. The entire arrangement was at earth
ground, so no floating elements. Some designs found in books and on the Web
feed them directly without the benefit of a balun. I've done it both ways
and have had great success.

"'Doc" wrote in message ...


Stephen Cowell wrote:

Plumber's Delight J-pole doesn't require
an insulator at all... I'd imagine that it could
take all the power you could pour into it,
probably take way over legal limit to melt
a half-inch copper pipe J-pole.

....

None at all? Are you real sure about that?
Think about it...

Well, you're welcome to come look in my garage...
I have a J-pole for 6 meters, shunt-fed. All parts
of the antenna/Q-line are at DC potential... it's
a solid piece of copper. You can ground the
'handle', hurts not a whit. If your J-pole has an
insulator in the middle, with a phasing section,
then it's a 'Super J', not a normal J. A normal
J-pole consists of the Q-line matching section
(the tuning fork part) and a half-wave radiator
just above that.
__
Steve
KI5YG
..

"John Smith" wrote in message
...

"'Doc" wrote in message ...


Stephen Cowell wrote:

Plumber's Delight J-pole doesn't require
an insulator at all... I'd imagine that it could
take all the power you could pour into it,
probably take way over legal limit to melt
a half-inch copper pipe J-pole.
__
Steve
KI5YG
.

None at all? Are you real sure about that?
Think about it...
'Doc


Yeah, no insulators at all... using plumber's delight.

The bottom of the J is strapped together. The feed point is then moved up
from the bottom along the 1/4 wave matching section until a match is
obtained.

This approach can be pretty nice. I used three sections of steel mast for
a
30 feet tall pipe, grounded at the bottom for lightning protection. I then
added a 1/4 wave piece of conduit 3/4 wave down from the top strapped with
sheet steel. Made a 1/2 wave balun from coax and found the lowest SWR feed
point along the matching section. The entire arrangement was at earth
ground, so no floating elements. Some designs found in books and on the
Web
feed them directly without the benefit of a balun. I've done it both ways
and have had great success.

What keeps the mast below the J pole from radiating?
Dale W4OP

"Dale Parfitt" wrote in message
...

"John Smith" wrote in message
...

"'Doc" wrote in message
...


Stephen Cowell wrote:

Plumber's Delight J-pole doesn't require
an insulator at all... I'd imagine that it could
take all the power you could pour into it,
probably take way over legal limit to melt
a half-inch copper pipe J-pole.
__
Steve
KI5YG
.

None at all? Are you real sure about that?
Think about it...
'Doc


Yeah, no insulators at all... using plumber's delight.

The bottom of the J is strapped together. The feed point is then moved
up
from the bottom along the 1/4 wave matching section until a match is
obtained.

This approach can be pretty nice. I used three sections of steel mast
for
a
30 feet tall pipe, grounded at the bottom for lightning protection. I
then
added a 1/4 wave piece of conduit 3/4 wave down from the top strapped
with
sheet steel. Made a 1/2 wave balun from coax and found the lowest SWR
feed
point along the matching section. The entire arrangement was at earth
ground, so no floating elements. Some designs found in books and on the
Web
feed them directly without the benefit of a balun. I've done it both
ways
and have had great success.

What keeps the mast below the J pole from radiating?
Dale W4OP


They tell me it's the 1/4-wave matching section which stops the rf from
moving on down the mast. A shorted 1/4 wave piece of transmission line looks
like an open circuit or essentially a choke to the antenna. In fact,
microstrip line construction uses 1/4 wave sections for RF chokes.

73,
John - KD5YI

"John Smith" wrote in message ...

What keeps the mast below the J pole from radiating?
Dale W4OP


They tell me it's the 1/4-wave matching section which stops the rf from
moving on down the mast. A shorted 1/4 wave piece of transmission line looks
like an open circuit or essentially a choke to the antenna. In fact,
microstrip line construction uses 1/4 wave sections for RF chokes.

73,
John - KD5YI


Yep. It was disscussed on this forum how with certain types of
waveguides, that every so often, there would be a 1/4 wave "insulator"
that would suspend the center conductor from the outer ground.

A short rotated 1/4 wavelength "towards the generator" on a Smith
Chart will tell you that electrically, it's virtually like an open.

But even when you know this, it's still kinda neat to think how it
really doesn't matter how long or how grounded the "handle" of the
J-pole is.

Very cool stuff.

Getting back to my question, i would say that i disagree that the
only limiting factor is the breakdown voltage of the insulators. The
limiting factor would be the current carrying capabilities of the
conductors themselves, and when you include the skin effect, a larger
diameter copper pipe can handle more current naturally.

I think a 3/4" J-pole should be able to handle 500 watts at least.


Dr. Slick