I decided to install a 2m FM rig in my garage to stay in touch with the
local repeaters while working on the car. I want a quick and dirty homebrew
antenna at the roof line. I know the J-pole is a popular 2m antenna, but
why??? The J-pole is basically a half wave antenna fed at the end, right? At
2m you are only 19 inches away from the 50 ohm feed point (a classic
dipole), so why not just loop the coax into the middle and forget the
matching stub? Am I missing something?

If I do this, would a clip on ferrite at the feed point make a good
choke-balun?

--
Bob D. ND9B

"Bob D." wrote in message
...
I decided to install a 2m FM rig in my garage to stay in touch with the
local repeaters while working on the car. I want a quick and dirty
homebrew
antenna at the roof line. I know the J-pole is a popular 2m antenna, but
why??? The J-pole is basically a half wave antenna fed at the end, right?
At
2m you are only 19 inches away from the 50 ohm feed point (a classic
dipole), so why not just loop the coax into the middle and forget the
matching stub? Am I missing something?

If I do this, would a clip on ferrite at the feed point make a good
choke-balun?

--
Bob D. ND9B

The coax must depart perpendicular from the 75 ohm feed point by .2 to .5
wavelength or greater for the Vertical dipole you describe. This makes it a
great tower side mount antenna with gain like a 2 element beam. When
mounted this way, the coax gets dressed down the tower leg and all is well
without ferrites.

J-pole is simple to build with 300 ohm TV twinnlead that was once cheap and
available anywhere. Also the J-pole includes a matching section to 50 ohms
.. Hang up one by a string, and roll it up for travel. Light weight and
slick. Vertical dipole needs something like a gamma match to get to 50
ohms, but 75 ohms isn't far off and the antenna is fairly broad too. A
variation is the coaxial dipole, that feeds the coax up a 1/2 wave mounting
pipe to the feedpoint and a 1/4 wave whip and larger 1/4 wave ground skirt.

On Thu, 28 May 2009 11:15:52 -0400, Bob D. wrote:

I decided to install a 2m FM rig in my garage to stay in touch with the
local repeaters while working on the car. I want a quick and dirty
homebrew antenna at the roof line. I know the J-pole is a popular 2m
antenna, but why??? The J-pole is basically a half wave antenna fed at
the end, right? At 2m you are only 19 inches away from the 50 ohm feed
point (a classic dipole), so why not just loop the coax into the middle
and forget the matching stub? Am I missing something?

If I do this, would a clip on ferrite at the feed point make a good
choke-balun?

There's not much performance difference between a J-pole, vertical
dipole, and a quarter-wave ground-plane vertical for working "local"
repeaters.

A J-pole for outdoor use can be easy to build, easy to mount, and very
rugged. For indoor use, you might want to settle for a simple twin-lead
J-pole, which is even easier to build and can be easy to mount.

A vertical dipole will tend to have a screwy radiation pattern if you
just run the coax up from below and connect to the middle. But probably
not enough for you to care.

I'd go with whatever seems easiest to make and easiest to mount in your
particular situation.

.... Rich W2RG

"Bob D." wrote in message
...
I decided to install a 2m FM rig in my garage to stay in touch with the
local repeaters while working on the car. I want a quick and dirty homebrew
antenna at the roof line. I know the J-pole is a popular 2m antenna, but
why??? The J-pole is basically a half wave antenna fed at the end, right?
At 2m you are only 19 inches away from the 50 ohm feed point (a classic
dipole), so why not just loop the coax into the middle and forget the
matching stub? Am I missing something?

If I do this, would a clip on ferrite at the feed point make a good
choke-balun?

--
Bob D. ND9B


Ho Bib

I have used the ferrite clip-on beads for 2 meter antennas. They work
well for me. You will be able to test them by assembling your simple
antenna and see how warm they get after transmitting.
Keep the coax perpendicular to the dipole, dont "loop" it back parallel to
the dipole.

Jerry KD6JDJ

On Thu, 28 May 2009 11:15:52 -0400, "Bob D."
wrote:

I know the J-pole is a popular 2m antenna, but
why???

Hi Bob,

Mostly because it serves vanity more than needed gain. If a lossy
rubber ducky can hit a repeater with full quietening, a J-pole has no
claim for need.

If I do this, would a clip on ferrite at the feed point make a good
choke-balun?

Go with your instincts there.

73's
Richard Clark, KB7QHC

In message , Richard Clark
writes
On Thu, 28 May 2009 11:15:52 -0400, "Bob D."
wrote:

I know the J-pole is a popular 2m antenna, but
why???

Hi Bob,

Mostly because it serves vanity more than needed gain. If a lossy
rubber ducky can hit a repeater with full quietening, a J-pole has no
claim for need.

If I do this, would a clip on ferrite at the feed point make a good
choke-balun?

Go with your instincts there.

What 'vanity' does a J-pole serve? It's a simple, efficient, endfed
halfwave (essentially a 'Zepp'), low angle radiation, easy to construct,
tune up, and mount on the top of a pole. I see no 'vanity'.
--
Ian

On Thu, 28 May 2009 22:30:20 +0100, Ian Jackson
wrote:

What 'vanity' does a J-pole serve? It's a simple,

Simple compared to something even more elaborate (11 out of 10), I
suppose, which would be more vainglorious.

efficient,

More efficient than a rubber ducky was allowed (the need for that
efficiency has been skirted, however), so the claim of efficiency
appeals to vanity when the difference was already noted. More
efficient than a rubber ducky giving full quietening? What does that
matter if not to suit vanity?

endfed
halfwave (essentially a 'Zepp')

Now there's vanity in its full glory with the trappings of provenance
(the hushed heritage of the era of the romantic Zeppelins). I bet
tagging it with the name Zepp adds 5dBd gain alone!

, low angle radiation,

Any lower angle than a rubber ducky? It is vanity to sneer at the
ducky, especially when it gets the job done without all this pomp and
circumstance.

easy to construct,

I presume this the vain form of "simple."

tune up, and mount on the top of a pole.

You can mount a rubber ducky on the top of a pole too, but suffer the
humiliation. No vanity boost in doing that, of course; so guilt
demands a J-pole.

I see no 'vanity'.

I can't either - not here in the basement where I can hit my buddy's
repeater a dozen miles away with a 1/2W HT driving a 6" whip. Note I
say that I "can," but I don't for the shame of not having a J-pole
mounted on a 20 foot mast. I only kerchunk it knowing full well my
buddies won't talk to me on my whip through their own J-Poles. Of
course this is ironic where the repeater is using a quarterwave
because it is:
1. Much simpler,
2. Vastly more efficient;
3. Has an immensely lower angle of radiation;
4. Is superior to tune up;
5. and is mounted on a really, really tall tower (not a pole).

73's
Richard Clark, KB7QHC

Richard Clark wrote:

I can't either - not here in the basement where I can hit my buddy's
repeater a dozen miles away with a 1/2W HT driving a 6" whip. Note I
say that I "can," but I don't for the shame of not having a J-pole
mounted on a 20 foot mast. I only kerchunk it knowing full well my
buddies won't talk to me on my whip through their own J-Poles. Of
course this is ironic where the repeater is using a quarterwave
because it is:
1. Much simpler,
2. Vastly more efficient;
3. Has an immensely lower angle of radiation;
4. Is superior to tune up;
5. and is mounted on a really, really tall tower (not a pole).


Oh dear, this sounds like another case of some poor innocent beaten with
a J-Pole when they were a child, leaving a lifelong hatred of the
infernal things.

I too was a victim of J-poling, those of us who are identified by the
strange double welts and scars, one large and one small. With years of
therapy, I can now stand to be in the same neighborhood with the evil
"Devil's Cane".

Ever notice that they resemble the dreaded Wouff Hong? The elders were
on to something.


Seriously though, they are just another antenna, and usually used for a
pretty simple purpose, that of hitting the local repeater. I've used
quarter wave, dipole and J-Pole, and yup, they hit the repeater. No
majick, just something to mess with.

Right now I am using a J-pole for a more important reason. My wife likes
the look better than a ground plane.

- 73 de Mike N3LI -

"Richard Clark" wrote in message
...
On Thu, 28 May 2009 22:30:20 +0100, Ian Jackson
wrote:

What 'vanity' does a J-pole serve? It's a simple,

Simple compared to something even more elaborate (11 out of 10), I
suppose, which would be more vainglorious.

efficient,

More efficient than a rubber ducky was allowed (the need for that
efficiency has been skirted, however), so the claim of efficiency
appeals to vanity when the difference was already noted. More
efficient than a rubber ducky giving full quietening? What does that
matter if not to suit vanity?

endfed
halfwave (essentially a 'Zepp')

Now there's vanity in its full glory with the trappings of provenance
(the hushed heritage of the era of the romantic Zeppelins). I bet
tagging it with the name Zepp adds 5dBd gain alone!

, low angle radiation,

Any lower angle than a rubber ducky? It is vanity to sneer at the
ducky, especially when it gets the job done without all this pomp and
circumstance.

easy to construct,

I presume this the vain form of "simple."

tune up, and mount on the top of a pole.

You can mount a rubber ducky on the top of a pole too, but suffer the
humiliation. No vanity boost in doing that, of course; so guilt
demands a J-pole.

I see no 'vanity'.

I can't either - not here in the basement where I can hit my buddy's
repeater a dozen miles away with a 1/2W HT driving a 6" whip. Note I
say that I "can," but I don't for the shame of not having a J-pole
mounted on a 20 foot mast. I only kerchunk it knowing full well my
buddies won't talk to me on my whip through their own J-Poles. Of
course this is ironic where the repeater is using a quarterwave
because it is:
1. Much simpler,
2. Vastly more efficient;
3. Has an immensely lower angle of radiation;
4. Is superior to tune up;
5. and is mounted on a really, really tall tower (not a pole).

73's
Richard Clark, KB7QHC

The 1/4 wave ground plane has a useless pattern. Main lobe at about 30
degrees above horizon, but broad enough to be usable and simple to build. I
have one as a receive antenna for duplex operation, shielded from the
transmit antennas by an air conditioner and vertical separation, feeding
several receivers with cavities. It is literally thrown on the roof and
coax is routed through the ductwork. Hasn't moved for 12 years. Hint: if
you use an SO-239, seal the center conductor so water wont run down the rod
and into the connector. Tape the coax connector tightly.

For frequencies below 220, it is best to put up an outside antenna. Above
those frequencies, RF gets out with much less shielding from the building.

J-poles, vertical dipoles have a more useful pattern below horizon. They
provide useful performance without being too large. The typical 2 meter
rubber ducky has anywhere from 6 to 20 db of loss. The typical 2m 5/8 and
5db 440 dual band mobile antenna will be noticeably better.

What's with all the EMO girl chatter?

"JB" wrote in message
...


The 1/4 wave ground plane has a useless pattern. Main lobe at about 30
degrees above horizon, but broad enough to be usable and simple to build.


The quarter-wave antenna's height above ground has much more to do with the
elevation angle than the fact that the antenna is a quarter-wave ground
plane. Using EZNEC, I see that a quarter wave antenna situated 3 wavelengths
above real/high accuracy ground of medium characteristics has a main lobe 4
degrees above the horizon. At that angle, the gain is 5.1 dBi. You can
confirm this if you have a copy of EZNEC.

John