Re: Wide bandwidth ladder line J-pole for 6-Meters

On Tue, 13 Jun 2006 14:27:14 -0700, "Chuck Olson"
<chuckolson01@xxxxxxxxxxxxxxxxxxxxx> wrote:


"Steve N." <stuevue.nouskuowuicuz@xxxxxxxxxxxxxxx> wrote in message
news:e6n2i3$pf0$1@xxxxxxxxxxxxxxxxxxxxxx

"Chuck Olson" <chuckolson01@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:Ts-dndx_b-BRkBPZnZ2dnUVZ_oydnZ2d@xxxxxxxxxxxxxx
Today I clipped out the connection I had made at the bottom of the
radiator,
and the SWR bandwidth remained 2MHz as is was with the connection. The
group
of SWR measurements moved up an average of 150 KHz from my readings with
the
connection, but otherwise the performance of the "Slim Jim"
configuration
is
identical. The length of the gap may now serve as a tuning mechanism,
which
wasn't a feature with the bottom connection, and the archives show some
builders made good use of that facility. Thanks for spotting the
similarity,
Jeff. My 6M antenna will no doubt be better for it.
73, Chuck


Chuck,
I searched on Slim-Jim. Let me see if I understand correctly.
Slim-Jim is a twin-lead or ladder-line type J antenna with the *top* of
the
half-wave (dual conductor) radiator ends connected.
Yours has the bottom of the 1/2 wave ends connected.

Yes, I conncted both top and bottom of the radiator to the previously
floating wire, and when I removed the bottom connection, the SWR bandwidth
remained as before, so the bottom connection does not appear to be
necessary. The top connection is very easy, and evidently that's all you
need, so no doubt about it - - it becomes a Slim-Jim.

Am I to understand that the Slim-Jim configuration and yours have very
similar SWR BW?

Yes.

This is good to know.

Then I'd like clarification on your comment:
"... If you analyze the operation of the very successful "Open Stub
J-Pole" that Arrow makes, you will find they use the 0.95 FV for both
the
radiator and the stub,..."

Can you be more specific about this. What is the electrical length of the
stub for said analysis? I like that design, though there is controversy
about it.

I'm old fashioned, so I use an HP17BII calculator which has a "solve"
function, and with the formula, LIN = 11811 / F(MHZ) / 4 x VF, given any two
of LIN, FMHZ, and FV, I can obtain the third for a 1/4 wave stub.

We find on the Arrow site http://www.arrowantennas.com/j-pole.html the
longest element for operation at 146 MHz is 57.5", and the shorter element
that makes the 1/4-wave stub is 19.25". With FMHZ = 146 and LIN = 19.25" we
solve for VF of that shorter element and get 0.95 (which refers to the free
space 1/4-wave as 1.00). Subtracting the 19.25 from 57.5 we get the radiator
length of 38.25". Since that is a 1/2-wave length, we divide by 2 so we can
use the 1/4-wave formula, and solving for VF we again get 0.95. I hope this
helps.


73, Steve, K9DCi



Best regards,

Chuck, W6PKP


My 2-meter ladderline j-pole is connected at the bottom of the
apparatus only, forming the hook of the so-called "J". Yours is
connected at the very top and very bottom, forming kind of a double
"J"?

bob
k5qwg
.

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