Re(2): [Antennas] J-pole gain compared to 1/4 wave GP

[DavidE Benedict]

Saturday June 30, 2007

antennas at mailman.qth.net
nss at mwt.net

nss at mwt.net writes:
what was the design of this "Stacked" unit?

Joe WB9SBD
>
>
>DavidE Benedict wrote:
>
>>***
>>I believe that a J-Pole is a lower-angle radiator than a classic 1/4 wave
>>vertical --concentrates emissions to lower levels, and this is therefore
>>"gain" at those lower angles. That is, practically speaking,better in
>such
>>as reaching repeaters from HT's. 
>>-- I once used a stacked (colinear) J-Pole with outstanding results on 2m
>>on a fieldday...really reached out.
>>
>>David
>>W7DBH

I modified the design shown in the 17th edition of the ARRL Antenna Book:
THE SUPER-J MARITIME ANTENNA, page 16-22, etc.

>From the bottom, it stacks up with 2 or more Sections above the U of the
J-type antenna...so... 

>From the bottom 
...is the 1/4 wave U (a vertically-oriented tuning stub), 
--- then a 1/2 wave Vertically Oriented Section, 
-- then a Horizontally Oriented 1/4 wave stub, 
-- then another 1/2 wave Vertically Oriented Section, etc. 
Of course you can go with more Horizontally Oriented Stubs and Vertically
Oriented Sections if you like. Nobody seems to use more than four
Vertically Oriented Sections.

I used 1/2 inch I.D. copper pipe for the U and for the Vertical Sections,
and 1/4 inch I.D. pipe & fittings for the 1/4 wave Horizontal Stubs. 
-- This increased diameter makes the antenna bandwidth cover most of the
2m band, and the Vertical Sections end up being actually a bit shorter
than classic computations suggest.
NOTE: I suppose that the stubs can be much smaller diameter conductor and
also made much more compact, but I don't know how the commercial antenna
makers do that latter trick.

First I made the basic J-Pole antenna from these described materials and
got it tuned up with an MFJ Antenna Analyzer. Then I made & installed the
Horizontally Oriented Stub, and retuned/trimmed the new top Vertically
Oriented Section with the Analyzer after adding that second Section.

On page 16-26 you see an example of how I physically formed the Stubs to
be somewhat circular to make the antenna a bit more aesthetic and compact.

I only soldered the stubs and elsewhere where necessary, so I would have
easy to handle portable sections. Then when portable and when stacking it
together I drilled and used stainless screws to make it mechanically and
electrically sound.

Worked like a champ.

You can possibly find this article by searching for it at the ARRL web
site.

Hope this helps....

David B.
 W7DBH