LAB wrote:
I have been surprised for the twin lead problems because i had already
made another Slim Jim using 2mm bare copper wire on the sides of a black
"electric" plastic tube (d=about 2cm) and I get the same good performances
of the copper tube...

The velocity factor of the insulated twinlead is much
lower than bare wires. If you don't understand velocity
factor, please study up on the subject. Velocity factor
can make as much as a 20% difference in element lengths
between bare wires and insulated twinlead. The
characteristic impedance is also different causing the
50 ohm feedpoint position to change.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On May 30, 10:33*am, Cecil Moore wrote:
LAB wrote:
* * I have been surprised for the twin lead problems because i had already
made another Slim Jim using 2mm bare copper wire on the sides of a black
"electric" plastic tube (d=about 2cm) and I get the same good performances
of the copper tube...

The velocity factor of the insulated twinlead is much
lower than bare wires. If you don't understand velocity
factor, please study up on the subject. Velocity factor
can make as much as a 20% difference in element lengths
between bare wires and insulated twinlead. The
characteristic impedance is also different causing the
50 ohm feedpoint position to change.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

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

Jimmie

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

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!

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.

"Sal M. Onella" wrote in message
...

"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.

Hi "Sal"

I share your thoughts about a pattern range. I recently talked my buddy
into writing a program that plots Elevation Plane patterns of an antenna
when scaled to a frequency sent from any Polar Orbiting Satellite. I use
it alot using the 137 MHz beacons sent from NOAA satellites. Some HAM
satellites could be used. There are also L-band beacons sent from the NOAA
satellites.

Jerry KD6JDJ

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

On Jun 2, 4:51*am, Ian Jackson
wrote:
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