[CoARES-D10] Update - D10 Wed. Post-Net Discussion

[Floyd Moore]

Rob Strieby wrote:
> 
> This email is an update to one sent yesterday.  I actually found the
> 1994 New Ham Companion article for the construction of the dual band,
> twin lead J-pole discussed below:
> http://www2.arrl.org/tis/info/pdf/9409061.pdf.
> 

... rest deleted...

I thought I would reply since I atarted one of the J-Pole message strings :-)
In my search for enlightenment with regard to J-Pole design, I have ound a few
things (and these were also stated in the excellent article that Rick posted 
earlier):
  1 - No one really knows how/why these work.  Everyone thinks its a simple 
   quarter wave end-fed dipole and a half wave tied together.  But everyone
   also stated that it takes a bit of "tweaking" to get the VSWR right.

  2 - The velocity factor is the crucial design factor.  If you don't know it
   your all messed up.  It varies with a number of factors, but a single type
   from the same manufacture is relatively constant.

  3 - Look at any 4 designs and the dimensions will change by +/- 1/2inch for
   the standard 146MHz design (50.25in to 50.75in).

  4 - These antenna work well, but they need to be tuned.  You WILL need a 
   good SWR meter (or antenna analyzer) to finish the antenna.

  5 - No-one know if a balun is required.  All articles but one (Rick's) say
   that the balun is required.

These lead me to believe that the construction is more trial and error that true 
design.  THat you should use the best numbers that you can find and then 
just build it and tune it afterward.

I now need to find the materials (easy, but I just don't have them handy) and
make one up.

Here are some interesting sites I found with J-Pole designs (not including the
ones already mentioned):

http://www.arrl.org/tis/info/JPole-V.html
http://www.arrl.org/news/features/1999/0615/4/
http://hamgate1.sunyerie.edu/races/antenna.htm
http://www.packetradio.com/ant.htm#jpoletv

Many more can be found with a google search with the term: "Twin-lead J-Pole"

Enjoy.

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