On Sat, 30 May 2009 12:38:08 -0700 (PDT), JIMMIE
wrote:

Whats the advantage of the Slim Jim over a plan old J antenna.

It has this coooool name that gives it at least 3.78dB advantage over
the name J-Pole (which, for the same nominal advantage (nominal
meaning name), has about a 5dBd gain over a rubber ducky).

If you want another 3dB nominal advantage, tag the word fractal to it:
Slim Jim Fractal J-Pole Antenna
of course, this being crass and a populist slant toward CBers, you
could tart the name up with academic trappings:
Slim Jim Fractal Gaussian Particels J-Pole Antenna
without bringing so much as 14.2dB loss for your effort.

Through the simple addition of a 2 meter sized dish, you can make it
omindirectional on the 160M band.

73's
Richard Clark, KB7QHC

JIMMIE wrote:
Whats the advantage of the Slim Jim over a plan old J antenna.

Apparently, the take-off-angle:

http://www.para.org.ph/membersarticl...Slim%20Jim.htm
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

I had already made another Slim Jim using 2mm bare copper wire on the
sides of a black "electric" plastic tube

The velocity factor of the insulated twinlead is muchlower than bare
wires. If you don't understand velocity factor, please study up on the
subject.

I know what is velocity factor. It is determined by L and C. In the
"other" Slim Jim a plastic tube was between the 2mm wires, but performances
was similar to the 6mm tube antenna, in which only air is between the tube

--
Gianluca

Apparently, the take-off-angle:

http://www.para.org.ph/membersarticl...Slim%20Jim.htm

I have *serious* doubts about the analysis in that article.

I believe that the author's assumption that splitting the radiator
current in half, and running it through two parallel elements, has the
effect of increasing the gain and dropping the takeoff angle is
incorrect.

The analysis I've read on Cebik's web site of J-poles of various sorts
seems to make no mention of this alleged effect. Nor have I seen it
discussed in writeups of folded dipoles.

If increasing the gain of a half-wave dipole were as easy as that,
it'd be a lot more popular a technique, and much better known.

I believe that a "slim jim" might have a slightly wider bandwidth
and/or lower resonant frequency than a single-wire J-pole of the same
dimensions, but more gain? Unless somebody's got independent evidence
of this (measurements or a good NEC model) I'd take it with a
good-sized grain of salt.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

LAB wrote:
I know what is velocity factor. It is determined by L and C. In the
"other" Slim Jim a plastic tube was between the 2mm wires, but performances
was similar to the 6mm tube antenna, in which only air is between the tube

The plastic tube had mostly air between the conductors.
The insulation on 300 ohm twinlead or window line is solid
dielectric around and between the two wires. VF is easy
enough to measure with something like an MFJ-259B.

I measured the VF of 300 ohm window line at 0.8
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

When I made the antenna I thought the plastic tube could do bad things.
I also read that black tubes have carbon in the plastic, then white ones
should be better...

--
Gianluca

Now it's very, very late here. I go to sleep. Have a good day!

--
Gianluca

On May 30, 8:30*pm, (Dave Platt) wrote:
Apparently, the take-off-angle:

http://www.para.org.ph/membersarticl...Slim%20Jim.htm

I have *serious* doubts about the analysis in that article.

I believe that the author's assumption that splitting the radiator
current in half, and running it through two parallel elements, has the
effect of increasing the gain and dropping the takeoff angle is
incorrect.

The analysis I've read on Cebik's web site of J-poles of various sorts
seems to make no mention of this alleged effect. *Nor have I seen it
discussed in writeups of folded dipoles.

If increasing the gain of a half-wave dipole were as easy as that,
it'd be a lot more popular a technique, and much better known.

I believe that a "slim jim" might have a slightly wider bandwidth
and/or lower resonant frequency than a single-wire J-pole of the same
dimensions, but more gain? *Unless somebody's got independent evidence
of this (measurements or a good NEC model) I'd take it with a
good-sized grain of salt.

--
Dave Platt * * * * * * * * * * * * * * * * * AE6EO
Friends of Jade Warrior home page: *http://www.radagast.org/jade-warrior
* I do _not_ wish to receive unsolicited commercial email, and I will
* * *boycott any company which has the gall to send me such ads!

Dave,That was my thoughts on it also. Two wires very close togethether
with in phase and more or less equal currents just adds up to a fatter
wire.

Jimmie

"JIMMIE" wrote in message
...

snip

Dave,That was my thoughts on it also. Two wires
very close togethether with in phase and more or
less equal currents just adds up to a fatter
wire.

Not a fatter wire with twice the current?

Recall the colinear J-pole, The two currents are stacked and fed in phase
by means of the phasing section. Yes, I realize the currents in the Slim
Jim would appear to cancel.

I'm going to have to build one of these and see what it does. I have a lot
of twinlead and I have a precision RF generator. I always wanted my own
antenna range; tomorrow's the day. Maybe Tuesday.

In message , Cecil Moore
writes
JIMMIE wrote:
Whats the advantage of the Slim Jim over a plan old J antenna.

Apparently, the take-off-angle:

http://www.para.org.ph/membersarticl...Slim%20Jim.htm

I'm sure that W4RNL did a comparison. It might be in here.
http://www.scribd.com/doc/8511817/Some-JPoles-That-I-Have-Known-4
http://www.cebik.com/
If it's not in there somewhere, a Google will be necessary.

Essentially, the answer was 'not a lot', except that the Slim Jim
version (the one with the folded-over top) had a slightly wider
bandwidth / flatter SWR plot.
--
Ian