Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Tooooo many opinions ....  (Read 1490 times)
KE4VCU
Member

Posts: 3




Ignore
« on: July 01, 2012, 01:37:22 PM »

When attaching leads to a copper tubing J-pole, does the solid center conductor go to the short side or the long side ?  My terms are not very technical, but it helps to minimize confusion.
Thank You.

Bobby
KE4VCU
Logged
KF6QEX
Member

Posts: 605




Ignore
« Reply #1 on: July 01, 2012, 01:52:00 PM »


http://www.alpharubicon.com/elect/jpolejaden.htm

http://en.wikipedia.org/wiki/File:Antenna-j-pole-diagram.svg


« Last Edit: July 01, 2012, 01:53:31 PM by KF6QEX » Logged
WB6BYU
Member

Posts: 13335




Ignore
« Reply #2 on: July 01, 2012, 03:19:04 PM »

It shouldn't make any difference.

In some cases it may, depending on the length of the coax and the mast, the exact
construction of the antenna, etc.  Either can work well in some situations and not
in others, but it is very difficult to know ahead of time.  So just choose whichever
is easier mechanically.
Logged
W5DXP
Member

Posts: 3613


WWW

Ignore
« Reply #3 on: July 02, 2012, 12:04:09 PM »

When attaching leads to a copper tubing J-pole, does the solid center conductor go to the short side or the long side ?

The J-Pole is not a well-engineered antenna and that's why you don't see many of them in commercial applications. It is good engineering practice to install a balun at every BALanced to UNbalanced junction in the system. There are two of those junctions in a J-Pole antenna and not a balun in sight unless one rolls an ugly balun at the feedpoint which is a mechanically difficult implementation. A J-Pole is basically a Zepp antenna for vhf/uhf and shares the same common-mode problems. One will have common-mode signals on the coax no matter which conductor goes where.

Has anyone tried feeding a J-Pole with twin lead attached at the 300 ohm feedpoint?
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
G4AON
Member

Posts: 542




Ignore
« Reply #4 on: July 02, 2012, 12:56:42 PM »

If you want to try a 6m J-Pole from 450 Ohm slotted ribbon, see my page at:
http://www.astromag.co.uk/j-pole/

73 Dave
Logged
KB5UBI
Member

Posts: 97




Ignore
« Reply #5 on: July 04, 2012, 12:21:46 PM »

Cecil,

I've built a few J-poles by feeding at the 200 ohm point using a 1/2 wave coax balun. I found them easier to tune and they loose their ground interaction. It was easy to find the 200 ohm spot by moving the feed point up and down until it had a 1:1 SWR.

I built a temporary one years ago for a Public Service repeater (460 mhz). You could use that San Antonio repeater from Austin with a mobile with the balanced fed J-Pole, but that went away when it was replaced with a commercial down-tilt antenna.

That said, I agree the J-Pole is a marginal design but it is easy to build.

KB5UBI
« Last Edit: July 04, 2012, 12:34:27 PM by KB5UBI » Logged
K5KNE
Member

Posts: 65




Ignore
« Reply #6 on: July 04, 2012, 02:05:21 PM »

Try it both ways and see which one seems to be better.  It has been either way sucessfully.

Walter K5KNE
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!