[Antennas] Re: "J" poles
Darryl J. Kelly
[email protected]
2002年7月11日 21:02:32 -0500
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