I have been trying to get an acceptable 2 meter antenna installed in
my attic. A J-Pole seemed to me the best solution for my attic space.
You may recall an earlier post where I discussed SWR on one of the
ladder line J-Poles I was working with. Well, I gave up on ladder line
and constructed a J-Pole from 1/2 inch copper tubing. I tuned it in my
basement work shop to give the best SWR and then took it up to the
attic. The following table shows the results.

Basement Attic

144 1.90 1.80
145 1.65 2.00
146 1.50 2.10
147 1.60 2.25
147.995 1.90 2.25

Actually, probably not that bad for a first attempt at copper tubing.
But, I didn't like the fact that SWR was above 2.0 in my attic and
that things changed between my basement shop and the attic. I guess
this design is influenced by objects close by.

So, somewhere in my surfing I came across the Arrow J-Pole. This is an
end fed, open stub commercial design that promises less that 1.5 SWR
across the band. Here are the results of my experiment with this antenna.

Basement Attic

144 1.10 1.22
145 1.18 1.10
146 1.25 1.20
147 1.30 1.32
147.995 1.40 1.42

Not 1.0 SWR but certainly met the promise. And the best thing about
this design is that near by objects don't seem to have an impact on
performance. If I built one of these designs and tuned it in my
basement shop, it should give the same results in the attic.

Anyway, just my subjective observations.

jimbo - AJ7IM

jimbo wrote:
I have been trying to get an acceptable 2 meter antenna installed in
my attic. A J-Pole seemed to me the best solution for my attic space.
You may recall an earlier post where I discussed SWR on one of the
ladder line J-Poles I was working with. Well, I gave up on ladder line
and constructed a J-Pole from 1/2 inch copper tubing. I tuned it in my
basement work shop to give the best SWR and then took it up to the
attic. The following table shows the results.

Basement Attic

144 1.90 1.80
145 1.65 2.00
146 1.50 2.10
147 1.60 2.25
147.995 1.90 2.25

Actually, probably not that bad for a first attempt at copper tubing.
But, I didn't like the fact that SWR was above 2.0 in my attic and
that things changed between my basement shop and the attic. I guess
this design is influenced by objects close by.

So, somewhere in my surfing I came across the Arrow J-Pole. This is an
end fed, open stub commercial design that promises less that 1.5 SWR
across the band. Here are the results of my experiment with this antenna.

Basement Attic

144 1.10 1.22
145 1.18 1.10
146 1.25 1.20
147 1.30 1.32
147.995 1.40 1.42

Not 1.0 SWR but certainly met the promise. And the best thing about
this design is that near by objects don't seem to have an impact on
performance. If I built one of these designs and tuned it in my
basement shop, it should give the same results in the attic.

Anyway, just my subjective observations.

jimbo - AJ7IM

Hi Jimbo, it has been my experience, and everybody else's that an
indoor or attic J-pole is unpredictable. A high impedance end fed
antenna in an attic environment will be hard to predict. Moving it one
foot can effect things.
You might consider the SO-239 ground plane. It can be built and
tuned in 30 minutes, is 50 ohms, so it will not be so concerned about
its environment. Likely you could not tell a difference in performance
from a J-pole especially if they are both in the attic.
Oh yes, the standard-if the SWR is below 3.0, don't worry about it.
Gary N4AST

On 25 Apr 2006 16:43:11 -0700, wrote:


jimbo wrote:
SNIP
jimbo - AJ7IM

Hi Jimbo, it has been my experience, and everybody else's that an
indoor or attic J-pole is unpredictable. A high impedance end fed
antenna in an attic environment will be hard to predict. Moving it one
foot can effect things.
You might consider the SO-239 ground plane. It can be built and
tuned in 30 minutes, is 50 ohms, so it will not be so concerned about
its environment. Likely you could not tell a difference in performance
from a J-pole especially if they are both in the attic.
Oh yes, the standard-if the SWR is below 3.0, don't worry about it.
Gary N4AST


I started building dipole antennas. they can be mounted horizontal or
vertical and easily moved around. I use cpvc with a dipole wire
inside and a coax-choke balun. They work quite well.

Just another option.
--
73 for now
Buck
N4PGW

The J-pole crowd seems to tout fantastic claims about this antenna and I
have never been impressed. Many people have tested the J-pole against
other easy to make antennas and the end fed half wave J-pole usually
does not stand up to even it’s brother, the center fed half wave dipole.
I assume the decrease in performance is due to mistakes in assembling
and tuning the matching section. Here is a link to a group that tested
some J-poles against other antennas in the CA desert and the J-pole lost
to even simple 1/4 wave ground plane types.
http://www.geocities.com/SiliconVall...5/anttest.html
My point is, why not make a simple ground plane for the attic that may
not get bothered by surroundings as much as the J-pole.
Bob


Buck wrote:
On 25 Apr 2006 16:43:11 -0700, wrote:

jimbo wrote:
SNIP
jimbo - AJ7IM
Hi Jimbo, it has been my experience, and everybody else's that an
indoor or attic J-pole is unpredictable. A high impedance end fed
antenna in an attic environment will be hard to predict. Moving it one
foot can effect things.
You might consider the SO-239 ground plane. It can be built and
tuned in 30 minutes, is 50 ohms, so it will not be so concerned about
its environment. Likely you could not tell a difference in performance
from a J-pole especially if they are both in the attic.
Oh yes, the standard-if the SWR is below 3.0, don't worry about it.
Gary N4AST


I started building dipole antennas. they can be mounted horizontal or
vertical and easily moved around. I use cpvc with a dipole wire
inside and a coax-choke balun. They work quite well.

Just another option.

Bob wrote:
snip

My point is, why not make a simple ground plane for the attic that may
not get bothered by surroundings as much as the J-pole.
Bob


I made one of those antennas right after I got my Tech license. Hit
the local repeater with no problems. I guess I forgot or thought it
was too simple for the current application.

jimbo

"Bob" wrote in message
. com...
The J-pole crowd seems to tout fantastic claims about this antenna and I
have never been impressed. Many people have tested the J-pole against
other easy to make antennas and the end fed half wave J-pole usually
does not stand up to even it’s brother, the center fed half wave dipole.
I assume the decrease in performance is due to mistakes in assembling
and tuning the matching section. Here is a link to a group that tested
some J-poles against other antennas in the CA desert and the J-pole lost
to even simple 1/4 wave ground plane types.
http://www.geocities.com/SiliconVall...5/anttest.html

snip

A quick look at the numbers doesn't make the j-pole look so all-fired bad.
"Losing" by 1 dB or so isn't a serious loss. Ham radio isn't exactly the
Kentucky Derby.

I don't know what "fantastic claims" you've heard, but my affinity for the
j-pole comes from its simplicity and durability. It's a halfwave vertical
that requires no ground plane and can often be matched to 1:1 at the sweet
spot. Mounting is a dream -- it even works if you drop the low end into a
plumbing vent pipe. (How would I know that? ;-)

I have never built a center-fed halfwave, but we use a bunch of them in the
Navy -- call them "stovepipes" because of the way the fiberglass housings
look -- and they work very, very well. The elements are large metal
cylinders, tending to make them quite broadband. I do not know how they're
fed ... balun or what.

John , KD6VKW

The J-pole crowd seems to tout fantastic claims about this antenna and I
....[snip]....

... my affinity for the j-pole comes from its simplicity and durability.
... Mounting is a dream -- it even works if you drop the low end into a
plumbing vent pipe. (How would I know that? ;-)
....[snip]....

I once made a J-pole from 300-ohm twinlead and tweaked it until it worked
OK while hanging from the ceiling, but when I moved it over next to a
wood-framed picture window (hung it from the window casing), the SWR went
to pot. Did I do something wrong?

(I concluded the J-pole must be VERY sensitive to its surroundings.)

--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)

Same here..in the attic...works great...even at 50w.

73 de KB9BVN


--
=========================================
Radio Amateurs - Fill your junk box, from my junkbox!
http://www.hamradparts.com
73 de KB9BVN
=========================================


"Buck" wrote in message
...
On 25 Apr 2006 16:43:11 -0700, wrote:


jimbo wrote:
SNIP
jimbo - AJ7IM

Hi Jimbo, it has been my experience, and everybody else's that an
indoor or attic J-pole is unpredictable. A high impedance end fed
antenna in an attic environment will be hard to predict. Moving it one
foot can effect things.
You might consider the SO-239 ground plane. It can be built and
tuned in 30 minutes, is 50 ohms, so it will not be so concerned about
its environment. Likely you could not tell a difference in performance
from a J-pole especially if they are both in the attic.
Oh yes, the standard-if the SWR is below 3.0, don't worry about it.
Gary N4AST


I started building dipole antennas. they can be mounted horizontal or
vertical and easily moved around. I use cpvc with a dipole wire
inside and a coax-choke balun. They work quite well.

Just another option.
--
73 for now
Buck
N4PGW

"jimbo" wrote in message
. ..
I have been trying to get an acceptable 2 meter antenna installed in
my attic. A J-Pole seemed to me the best solution for my attic space.
You may recall an earlier post where I discussed SWR on one of the
ladder line J-Poles I was working with. Well, I gave up on ladder line
and constructed a J-Pole from 1/2 inch copper tubing. I tuned it in my
basement work shop to give the best SWR and then took it up to the
attic. The following table shows the results.

Basement Attic

144 1.90 1.80
145 1.65 2.00
146 1.50 2.10
147 1.60 2.25
147.995 1.90 2.25

Actually, probably not that bad for a first attempt at copper tubing.
But, I didn't like the fact that SWR was above 2.0 in my attic and
that things changed between my basement shop and the attic. I guess
this design is influenced by objects close by.

So, somewhere in my surfing I came across the Arrow J-Pole. This is an
end fed, open stub commercial design that promises less that 1.5 SWR
across the band. Here are the results of my experiment with this antenna.

Basement Attic

144 1.10 1.22
145 1.18 1.10
146 1.25 1.20
147 1.30 1.32
147.995 1.40 1.42

Not 1.0 SWR but certainly met the promise. And the best thing about
this design is that near by objects don't seem to have an impact on
performance. If I built one of these designs and tuned it in my
basement shop, it should give the same results in the attic.

Anyway, just my subjective observations.



Not to detract from the other posters ... IMO they all made valid comments,
but I offer this:

As the builder of about 20 copper pipe j-poles, I discovered that I can get
a better final VSWR if I include a 100 pF (or so) cap in the side fed by the
coax center.

I had been attaching an SO-239-type bulkhead connector to the short side of
the J and running a piece of solid wire from the center pin over to the long
side of the J. I could get the VSWR to a dip near the middle of the band by
monkeying with the feed point and/or trimming the length but the lowest I
usually got was around 1.5 : 1. As soon as I used the cap in place of the
straight wire, I could get 1:1. It works for me ... your mileage may vary.

I built more j-poles for 2M than all the others combined and 20 is not a lot
of antennas. For some reason, the cap seems to help the 2M size more than
it helps the others, but these antennas are too few in number for scientific
judgements by this amateur plumber.

73,
John

jimbo wrote:
I have been trying to get an acceptable 2 meter antenna installed in my
attic. A J-Pole seemed to me the best solution for my attic space. You
may recall an earlier post where I discussed SWR on one of the ladder
line J-Poles I was working with. Well, I gave up on ladder line and
constructed a J-Pole from 1/2 inch copper tubing. I tuned it in my
basement work shop to give the best SWR and then took it up to the
attic. The following table shows the results.

Basement Attic

144 1.90 1.80
145 1.65 2.00
146 1.50 2.10
147 1.60 2.25
147.995 1.90 2.25

Actually, probably not that bad for a first attempt at copper tubing.
But, I didn't like the fact that SWR was above 2.0 in my attic and that
things changed between my basement shop and the attic. I guess this
design is influenced by objects close by.

So, somewhere in my surfing I came across the Arrow J-Pole. This is an
end fed, open stub commercial design that promises less that 1.5 SWR
across the band. Here are the results of my experiment with this antenna.

Basement Attic

144 1.10 1.22
145 1.18 1.10
146 1.25 1.20
147 1.30 1.32
147.995 1.40 1.42

Not 1.0 SWR but certainly met the promise. And the best thing about this
design is that near by objects don't seem to have an impact on
performance. If I built one of these designs and tuned it in my basement
shop, it should give the same results in the attic.

Anyway, just my subjective observations.

jimbo - AJ7IM

I guess my conclusion is that the conventional J-Pole design seems to
be more susceptible to near by objects than the much less common end
fed, open stub, J-Pole. My conventional copper J-pole changed much
more than the end fed Arrow J-Pole when moved from the basement to the
attic. And I have noticed on other occasions that even very small
changes in location and/or orientation had a large effect on SWR.

The ARRL Antenna Book has a small section on J-Pole antennas. They
show both designs, conventional shorted stub and the uncommon end fed,
open stub designs. They say that the shorted stub design should have a
4/1 balun at the feed point because a direct coax connection results
in extreme sensitivity to near by objects. And they also say the end
fed, open stub design doesn't require a balun and is much less
sensitive to near by objects, but is harder to tune. (I don't
understand that point, there is one less parameter to fiddle with.)

All of this leads me to wonder why almost all J-Pole designs one sees
are of the shorted stub version and almost none use a balun. I suspect
ease of construction and low cost. My "store bought" Arrow end fed,
open stub, J-Pole seems to verify the ARRL Antenna Book's conclusions
about sensitivity to near by objects. However, do-it-yourself
construction does appear to be much more difficult. I may give it a
try, just out of curiosity.

A final note. My attic is a very difficult place to work. There is no
way I can install an antenna and then make numerous adjustments to get
it tuned to the space. I must be able to do any required tuning in my
basement shop or maybe outside on my deck and then take it to the
attic for installation. So for my application, I want something that
is not sensitive to near by objects. The end fed, open stub J-Pole
seems to fit that requirement.

73s jimbo