RadioBanter - View Single Post - Advice Needed for Super J-Pole Design: Inductive Loops Overheating

January 19th 04, 04:14 PM

(Dr. Slick) wrote in message

Can i get away without using the inductive loops? They are
supposed to be there to prevent the current from going down the
outside braid, right?
Yep, and it's obvious they are really needed in your case. I'm talking
big time...If you neglect that decoupling, the current flowing on the
shield of the coax will skew your pattern up off the horizon. That
will ruin any gain you might see over a 1/4 GP or whatever.

Or perhaps i can make fewer turns, or larger diameter loops? So
that the
impedance discontinuity is less severe at this point?

You will then be reducing the choking of the currents. Not good.

Knowledgable advice much appreciated.

You are seeing why I've never been a fan of those J poles...Frankly, I
think they are weird the way most people build them. And the 1/4 stub
is not even needed if they are using the "tuning ring" setup. Check
out a cushcraft ringo ranger. I prefer the RR design over that "super
J-pole", and even the ringo ranger suffers from a lack of decoupling.
Thats why they came out with the ringo ranger 2. It has a lower
decoupling section, which is a 50 inch piece of coax, which drops
below the feedpoint, parallel with the mast, and then is attached to a
union where the shield of the coax is grounded to the mast. A set of
1/4 wave radials are used at that point as the decoupling device. This
would work with your antenna. But me...I'd rebuild the whole dang
thing over again. :/ I prefer the dual 5/8 wave designs with a lower
1/4 wave decoupling section. IE: copy a isopole, or electrical
clone...You could rebuild a copper J pole to be a ringo ranger 2 clone
fairly easy. That design , while not perfect, does work quite well.
But a tad less than the old isopoles used to do. The isopole was
probably the best dual 5/8 design ever made as far as decoupling of
the feedline. MK