[Antennas] Re: "J" poles

[j. keith carter]

Hi Darryl; Have a look at the article in QST, April 1995, p74-75 by Dr. John (
Jack ) S. Belrose (Ph.D.), VE2CV,  titled " Designing a Vertical J Antenna".
Jack's article explores the aspect of length-diameter ratio to resonance. I got
involved in this a number of years back while trying to learn the modeling
aspects of EZNEC. An interesting aspect of using Jack's procedure is that one
can actually decrease the radiation angle, albeit by a couple of degrees, by
getting the length/diameter/resonance correct. Private correspondence confirmed
my findings although at the end of the day the outcome was one probably wouldn't
see any difference in operation. As mentioned in other postings on this subject,
the use of a balanced feed could be critical for optimum performance. Jack's
preference was to use a "bead" balun of the W2DU style for coax to balanced feed
at the quarter wave stub. Hope this adds to all the other excellent postings on
this subject. Keith, VE3JKC. a ps: it's interesting that for what ever reason
Jack called it a "vertical J antenna" . Also the article has all the formulas.

"Darryl J. Kelly" wrote:

> While we are on the subject of j poles, I would like to ask if anyone has a
> set of formulas for making a j-pole to resonate at a certain frequency. Most
> every article that I have seen has simply says make  the j-pole to these
> demensions. What if you make it to those demensions and it tunes to a
> different frequency than the author claims. What do you change, the long
> section, the tuning stub, the distance of the stub from main element, where
> and how is the thing to be fed, what if the SWR is higher than expected,
> etc. I have not found a definitive article that simply says for a j-pole of
> this frequency, use this formula for long element, etc, for wire or copper
> pipe, use this conversion. My best j-pole is in my attic, using a section of
> 450 ohm ladder line for matching stub, and fed with RG-8X. It's very flat
> across the whole 2 meter band, with just a slight rise in SWR at the top and
> bottom of the band. It was installed and then final tuned in place with an
> MFJ antenna analyzer. Someone should write a book on j-poles. Hope this is
> of interest.
> 73,
> Darryl, KK5IB
>