"Richard Clark" wrote
This will be news to the FCC and AM broadcast stations
Hi OM, Send them a singing telegram.
_______________

I'll leave that to you, as the author of the news.

wrote:

Since this is a 1/2 wave
antenna with a 1/4 matching section (3/4 overall),

Why the 1/4 matching section?

An 1/2WL end-fed with 1/4WL matching section is a Zepp.
--
73, Cecil http://www.qsl.net/w5dxp

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To put everyone "on the same page", here is a good description of what I
intend when I mention "slim jim."
http://www.hamuniverse.com/slimjim.html

Regards
--
Hay, if'n ya'll cun't konstructivly partecipete in this disscusion, haw
aboot speel-checkin it fer me?


wrote in message
ups.com...
....Anyone ever done a helical wound "Slim Jim?"
yes.
Since this is a 1/2 wave
antenna with a 1/4 matching section (3/4 overall),

Why the 1/4 matching section? Seems that takes it
nearly to the full half wave length...or close
enough not to matter much...
Myself, I would probably prefer a "gamma loop"
type matching scheme, which adds no height.
To me, 16 ft tall is no more trouble than 12 ft tall
in the real world.
I've had a lightweight 32 ft self supporting radiator
up, which was no hassle at all...And the base of that
was at 36 ft on a mast. "68 ft tall total".
That was a dual band 40m GP/ 17m 5/8 GP....Full size
on both bands, relay switched.

helical winding of this form into a 3/8 overall height
(approx. 12 ft. @ 28Mhz) might be possible.
The extremely low angle of radiation (approx. 8 degrees)
would make this vertical antenna desirable... ......................

The angle of maximum radiation will vary fairly
drastically depending on height above ground.
For a "like" sized vertical, the height above
ground will have more of an effect, than any
extra electrical length. To my way of thinking,
the advantage of the extended winding should be
the largest, the closer to ground it is.
The higher above ground, approaching 1/2 wave up,
the lesser the advantage.
Note that at high heights above ground in WL,
the 1/4 wave ground plane, and the 1/2 wave
vertical have nearly the same gain for practical
purposes. "maybe .3 -.8 db difference..."
You should consider decoupling of the antenna
from the feedline also. Radiation from the line
will skew the pattern upwards off the horizon.
This will ruin even higher gain collinears.

I like my antennas full size if at all possible.
I'm a radio bully. :/ MK

On Mon, 28 Mar 2005 06:22:05 -0600, "Richard Fry"
wrote:

"Richard Clark" wrote
This will be news to the FCC and AM broadcast stations
Hi OM, Send them a singing telegram.
_______________

I'll leave that to you, as the author of the news.

Not as important as you first thought I see - which was my point.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote wrote:
"Richard Clark" wrote
This will be news to the FCC and AM broadcast stations
Hi OM, Send them a singing telegram.
I'll leave that to you, as the author of the news.
Not as important as you first thought I see - which was my point.
__________________

Readers will judge for themselves as to the importance and validity of our
respective statements on this topic. You chose to avoid commenting about
the accuracy of what I posted, replying instead with a flip comment. I
suspect you know that what I posted was valid -- even though counter to your
point of view.

RF

On Mon, 28 Mar 2005 12:17:59 -0600, "Richard Fry"
wrote:
I suspect you know that what I posted was valid -- even though counter to your
point of view.
Knowing Pi out to seventeen places neither validates nor refutes the
shape of a pie. The evidence of correspondence proves my point: it
doesn't really matter given the greater bulk of your responses lie
outside of technical offerings - such data rich marginalia still fails
to elevate its pretenses above a trivial concern.

73's
Richard Clark, KB7QHC

....Anyone ever done a helical wound "Slim Jim?"
yes.
Since this is a 1/2 wave
antenna with a 1/4 matching section (3/4 overall),

Why the 1/4 matching section? Seems that takes it
nearly to the full half wave length...or close
enough not to matter much...
Myself, I would probably prefer a "gamma loop"
type matching scheme, which adds no height.
To me, 16 ft tall is no more trouble than 12 ft tall
in the real world.

SNIP

The SlimJim resembles the J-Pole. The 1/4 wave section is a matching
network and it is probably not critical that it be vertical so the
height may be reduced by about 1/3. I am not sure what the folded
section does for it. but without the 1/2 wave section coming back
down from the top, the antenna is just a J-Pole.




helical winding of this form into a 3/8 overall height
(approx. 12 ft. @ 28Mhz) might be possible.
The extremely low angle of radiation (approx. 8 degrees)
would make this vertical antenna desirable... ......................

I like my antennas full size if at all possible.
I'm a radio bully. :/ MK

I am with you here, when it is possible and practical.


--
73 for now
Buck
N4PGW

In article ,
Buck wrote:

The SlimJim resembles the J-Pole. The 1/4 wave section is a matching
network and it is probably not critical that it be vertical so the
height may be reduced by about 1/3. I am not sure what the folded
section does for it. but without the 1/2 wave section coming back
down from the top, the antenna is just a J-Pole.

The Slim Jim appears to be identical to the "top wire double radiator"
J-pole which is described in Cebik's multi-part discussion of J-pole
designs: see http://www.cebik.com/vhf/jp2.html

His analysis suggests that the performance and behavior of this type
of J-pole are essentially identical to those of a single-radiator
J-pole. There are some slight changes needed in the antenna
dimensions to get it resonated properly (the coax attachment point is
a fraction of an inch higher up and the total length is a bit
different) but once those are taken into account there doesn't seem to
be any real difference in performance between this variant, a
version with two wires which are left unconnected at the top, and a
version with one wire.

At their best, they appear to be simple 1/2-wave radiators. The hype
on the HamUniverse page about this antenna outperforming "1/2wave over
1/2wave over 1/2wave colinear!" seems a bit overdone - if it's ever
true, it would be in comparison to a rather badly-done colinear!

My expectation is that one could create a helically-wound version of
any of these J-pole versions. The matching arrangement would no doubt
need some adjustment. I'd expect the gain to drop off, with more
high-angle radiation appearing, in the usual fashion as the total
length of the radiating section is shortened.

--
Dave Platt AE6EO
Hosting the 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!

Buck wrote:
The SlimJim resembles the J-Pole.

And the Zepp.

I am not sure what the folded section does for it.

Folding a 1/4WL vertical raises the feedpoint impedance.
Folding a 1/2WL vertical lowers the feedpoint impedance.

A folded 1/2WL monopole has about half the end-fed feed-
point impedance of an end-fed single-wire 1/2WL monopole.
About 1250 ohms Vs 2500 ohms for 20m with mininec ground.

EZNEC sez the folded 1/2WL monopole has a slightly lower
resonant frequency and slightly higher gain. (+0.07 dB)
--
73, Cecil http://www.qsl.net/w5dxp

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Interesting... so electrical length is affecting gain and EZNEC supports
it--that will probably silence those who claim the physical length is all
important... ya suppose?

Regards

--
Hay, if'n ya'll cun't konstructivly partecipete in this disscusion, haw
aboot speel-checkin it fer me?


"Cecil Moore" wrote in message
...
Buck wrote:
The SlimJim resembles the J-Pole.

And the Zepp.

I am not sure what the folded section does for it.

Folding a 1/4WL vertical raises the feedpoint impedance.
Folding a 1/2WL vertical lowers the feedpoint impedance.

A folded 1/2WL monopole has about half the end-fed feed-
point impedance of an end-fed single-wire 1/2WL monopole.
About 1250 ohms Vs 2500 ohms for 20m with mininec ground.

EZNEC sez the folded 1/2WL monopole has a slightly lower
resonant frequency and slightly higher gain. (+0.07 dB)
--
73, Cecil http://www.qsl.net/w5dxp

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