Hi NG

I am in the throes of building an omni for 2m and am trying to decide
between a "super jpole" and an extended double zepp. I have more or less
gone for 5/8 over 5/8 radiators with a center "hairpin" phasing section.

The J-Pole is of course fed through the usual "hairpin" arrangement at
the bottom of the antenna. The EDZ at the center phasing/hairpin section.

Okay so here are the questions/thoughts.

- I don't mind mind mounting on the side of the mast. The whole thing
will eventually be rotatable and the mast itself might be a useful
reflector for a few more dB of fwd gain. This also makes the EDZ
reasonably easy to feed.

- I know of the issues with radiating feedline and pattern lifting for
the jpole. Wondering if a 4:1 coaxial balun would resolve this and also
give a wider VSWR bandwidth?

- I also note the J-Pole hairpin/matching section is never quite
balanced as the load Z at the connected vs non connected ends skews it
some. (From cebik) To my mind this has two thoughts, is it worth skewing
the feed point (eg one side of the feedpoint 1/2" below the other) and
does (static/lighting) grounding the supposed electrically neutral point
affect the efficiency/pattern of the thing.

- Wondering if feeding from one end results in ohmic losses reducing the
radiation from the upper element. Thus skewing the pattern undesirably
upwards. I heard this use to be a big problem with early UHF coaxial
collinear antennas. Mounting upside down was supposedly a good fix!

- I had thought for ages that skying radiation from ground effects is
actually a function of the amount of radiation that goes at a downwards
angle. (ie a perfect antenna is one that doesn't radiate below the
"horizon" in free space) If one uses a 5/8 element for the antenna's
mentioned above the normal high lobe one gets might contribute to this
problem. In other words is it better to (say) use 3x1/2 wave rather than
2x5/8 wave elements in either an EDZ or JPole setup. (I'll be modeling
this for my own interest but would appreciate feedback)

- This of course begs the question as to whether one should even be
concerned about ground reflection on 2m with a 30ft mast!

This topic can of course be very exhausting. In my case though it is
more to decide which device to build.

Tnxs for any thoughts and ideas.

Bob W5/VK2YQA

On Sat, 03 Feb 2007 18:29:41 -0600, Bob Bob
wrote:

- I know of the issues with radiating feedline and pattern lifting for
the jpole. Wondering if a 4:1 coaxial balun would resolve this and also
give a wider VSWR bandwidth?

Hi Bob²,

Nope. The width is determined by Q. Pattern is determined by
physical vs. electrical size. Neither of those is dependent on a
BalUn. Now a BalUn as Choke may aid in pattern; and this is the
conventional failing point for J-poles. As for using a 4:1, what for?
Isn't the J-pole designed for a match already? If not, go a more
conventional route.

- I also note the J-Pole hairpin/matching section is never quite
balanced as the load Z at the connected vs non connected ends skews it
some. (From cebik) To my mind this has two thoughts, is it worth skewing
the feed point (eg one side of the feedpoint 1/2" below the other) and

Skewing, as you use it, is somewhat ambiguous. Moving the tap will
move the match, not the balance. Further, it will probably increase
what you perceive to be a problem.

does (static/lighting) grounding the supposed electrically neutral point
affect the efficiency/pattern of the thing.

It is actually, electrically grounded. Being neutral is a condition
of wavelength and distance. The combination of those two find a point
that is insensitive to attachment (there are folded dipoles that mount
this way).

- Wondering if feeding from one end results in ohmic losses reducing the
radiation from the upper element.

Ohmic losses will remain regardless of where you excite an antenna.
That is, unless you remove the loss. You don't say how you accomplish
THAT by moving the feed.

Thus skewing the pattern undesirably upwards.

A different skewing I see.

I heard this use to be a big problem with early UHF coaxial
collinear antennas. Mounting upside down was supposedly a good fix!

Yeh, sure.

- I had thought for ages that skying radiation from ground effects is

Skying? More skewing? Ground "effects?" An air dam for the bumper
of your antenna?

actually a function of the amount of radiation that goes at a downwards
angle. (ie a perfect antenna is one that doesn't radiate below the
"horizon" in free space)

Umm, perhaps.

If one uses a 5/8 element for the antenna's
mentioned above the normal high lobe one gets might contribute to this
problem.

5/8ths antennas were never built for problems, how did they suddenly
arrive at this juncture?

In other words is it better to (say) use 3x1/2 wave rather than
2x5/8 wave elements in either an EDZ or JPole setup. (I'll be modeling
this for my own interest but would appreciate feedback)

No. They are two distinctly different antennas. Note that 12/8ths
does not equal 10/8ths. Note even remotely.

- This of course begs the question as to whether one should even be
concerned about ground reflection on 2m with a 30ft mast!

Concerned? You sure have your priorities mixed. Maybe you should
dive right into modeling and resolve this through lifting a simpler
antenna through various elevations to find out what the consequences
are. They are many and varied.

73's
Richard Clark, KB7QHC

Hi,
Hey, those "J" pole designs from off the `web you see are pretty
much Plug & Play for the most part. If you go through the steps
listed in the construction plans, everything's been already worked out
for you. . . These antennas are extremely solid for the most part,
and I've found that they work darn well at thirty feet up, grounded
and un-grounded too.

The only reason I could see for re-working this wheel, is if you
were going to mount it real close to a metal structure or of you were
going to try and parallel them for some strange reason, then you'd
need to do the required math. However, that would only be relative to
the distance between items, not the individual matching. .. Just a
simple attachment to the right location on the antenna, and you are up
and running.

Trying to tweak anymore out of one of these things nowadays with all
the bugs already worked out for you is like trying to squeeze out a
few more ounces of torque from your lawnmower: It may be possible
with great effort, time, and money. . . But why bother?

With my copper pipe "J" pole, I had a 1.1:1 match, and was hitting
repeaters 200 miles away on 50 watts. . . No calcs. Just lay it out,
solder it up and stick it up into the air! About three hours from
"Pipe" to "Antenna".




On Sat, 03 Feb 2007 18:29:41 -0600, Bob Bob
wrote:

Hi NG

I am in the throes of building an omni for 2m and am trying to decide
between a "super jpole" and an extended double zepp. I have more or less
gone for 5/8 over 5/8 radiators with a center "hairpin" phasing section.

The J-Pole is of course fed through the usual "hairpin" arrangement at
the bottom of the antenna. The EDZ at the center phasing/hairpin section.

Okay so here are the questions/thoughts.

- I don't mind mind mounting on the side of the mast. The whole thing
will eventually be rotatable and the mast itself might be a useful
reflector for a few more dB of fwd gain. This also makes the EDZ
reasonably easy to feed.

- I know of the issues with radiating feedline and pattern lifting for
the jpole. Wondering if a 4:1 coaxial balun would resolve this and also
give a wider VSWR bandwidth?

- I also note the J-Pole hairpin/matching section is never quite
balanced as the load Z at the connected vs non connected ends skews it
some. (From cebik) To my mind this has two thoughts, is it worth skewing
the feed point (eg one side of the feedpoint 1/2" below the other) and
does (static/lighting) grounding the supposed electrically neutral point
affect the efficiency/pattern of the thing.

- Wondering if feeding from one end results in ohmic losses reducing the
radiation from the upper element. Thus skewing the pattern undesirably
upwards. I heard this use to be a big problem with early UHF coaxial
collinear antennas. Mounting upside down was supposedly a good fix!

- I had thought for ages that skying radiation from ground effects is
actually a function of the amount of radiation that goes at a downwards
angle. (ie a perfect antenna is one that doesn't radiate below the
"horizon" in free space) If one uses a 5/8 element for the antenna's
mentioned above the normal high lobe one gets might contribute to this
problem. In other words is it better to (say) use 3x1/2 wave rather than
2x5/8 wave elements in either an EDZ or JPole setup. (I'll be modeling
this for my own interest but would appreciate feedback)

- This of course begs the question as to whether one should even be
concerned about ground reflection on 2m with a 30ft mast!

This topic can of course be very exhausting. In my case though it is
more to decide which device to build.

Tnxs for any thoughts and ideas.

Bob W5/VK2YQA

Hi Fred

Tnxs for your comments

The issue however isn't to do with the (available) design of the JPole
itself, but whether it is better to use an EDZ instead of it. ie What
are the disadvantages/advantages. The points I made were the ones I was
"using" in the decision making process. You'll also note that I am
looking at the "Super 5/8-5/8 JPole" of which there are far fewer
designs available.

Cheers Bob VK2YQA

Fred Ferley wrote:

Hi,
Hey, those "J" pole designs from off the `web you see are pretty
much Plug & Play for the most part.