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J-Pole vs Slim Jim?



 
 
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  #1  
Old February 7th 07, 04:04 PM posted to rec.radio.amateur.antenna
Ian Jackson
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Posts: 89
Default J-Pole vs Slim Jim?

The J-Pole and the Slim Jim are both are essentially the same antenna.
However, is there any advantage in the Slim Jim's bit which folds back
down, or is it just there for decoration?
Ian.
--

  #2  
Old February 7th 07, 11:48 PM posted to rec.radio.amateur.antenna
Bob Bob
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Posts: 85
Default J-Pole vs Slim Jim?

H Ian

Mr Cebik had something to say about this...

http://www.cebik.com/vhf/jp2.html

Very intersting all around read on his whole website!

Cheers Bob VK2YQA



Ian Jackson wrote:

However, is there any advantage in the Slim Jim's bit which folds back
down, or is it just there for decoration?

  #3  
Old February 8th 07, 03:24 AM posted to rec.radio.amateur.antenna
art
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Posts: 1,189
Default J-Pole vs Slim Jim?

On 7 Feb, 15:48, Bob Bob wrote:
H Ian

Mr Cebik had something to say about this...

http://www.cebik.com/vhf/jp2.html

Very intersting all around read on his whole website!

Cheers Bob VK2YQA



Ian Jackson wrote:
However, is there any advantage in the Slim Jim's bit which folds back
down, or is it just there for decoration?- Hide quoted text -


- Show quoted text -


If you have room for a double Zepp then the best bet is the Moxon
dipole
with a resonator. It will supply the same gain as a zepp and has the
advantage
of operation over an octave by varying the value of the capacitor from
which
the resonatator is made of. This also removes the added coax stub
procedure.
required of a zepp.
Art
Art

  #4  
Old February 9th 07, 11:06 AM posted to rec.radio.amateur.antenna
Ian Jackson
external usenet poster
 
Posts: 89
Default J-Pole vs Slim Jim?

In message , Bob Bob
writes
H Ian

Mr Cebik had something to say about this...

http://www.cebik.com/vhf/jp2.html

Very intersting all around read on his whole website!

Cheers Bob VK2YQA



Ian Jackson wrote:

However, is there any advantage in the Slim Jim's bit which folds back
down, or is it just there for decoration?


Thanks, Bob.
I did have a look around, but I missed that particular paper in W4RNL's
website (which is certainly a mine of information).

The gist of it is that there is negligible difference between the three
versions of this antenna.

One point which I did notice is that the feed point is lowest down for
the single-radiator J-Pole (Fig 2), higher for the 'Loose Wire' version
(Fig 4), and highest for the folded-over Slim Jim version (Fig 6).
Presumably, this is because the top part is effectively fatter for the
Loose Wire, and fatter still for the Slim Jim. This will lower the
impedance at the bottom of the top halfwave part, and you will need to
tap the feeder further up the quarterwave stub in order to find the 50
ohm point. There is maybe some confirmation of this in the SWR plots
(Fig 11), where the bandwidth for the Slim Jim version is somewhat
greater than the other two.

I'm guessing that you would only make a Loose Wire version if you were
making the antenna out of twin feeder.

Cheers,
Ian.
--

  #5  
Old February 10th 07, 02:55 PM posted to rec.radio.amateur.antenna
JIMMIE
external usenet poster
 
Posts: 625
Default J-Pole vs Slim Jim?

On Feb 9, 6:06 am, Ian Jackson
wrote:
In message , Bob Bob
writes





H Ian


Mr Cebik had something to say about this...


http://www.cebik.com/vhf/jp2.html


Very intersting all around read on his whole website!


Cheers Bob VK2YQA


Ian Jackson wrote:


However, is there any advantage in the Slim Jim's bit which folds back
down, or is it just there for decoration?


Thanks, Bob.
I did have a look around, but I missed that particular paper in W4RNL's
website (which is certainly a mine of information).

The gist of it is that there is negligible difference between the three
versions of this antenna.

One point which I did notice is that the feed point is lowest down for
the single-radiator J-Pole (Fig 2), higher for the 'Loose Wire' version
(Fig 4), and highest for the folded-over Slim Jim version (Fig 6).
Presumably, this is because the top part is effectively fatter for the
Loose Wire, and fatter still for the Slim Jim. This will lower the
impedance at the bottom of the top halfwave part, and you will need to
tap the feeder further up the quarterwave stub in order to find the 50
ohm point. There is maybe some confirmation of this in the SWR plots
(Fig 11), where the bandwidth for the Slim Jim version is somewhat
greater than the other two.

I'm guessing that you would only make a Loose Wire version if you were
making the antenna out of twin feeder.

Cheers,
Ian.
--- Hide quoted text -

- Show quoted text -


Once upon a time I was experimenting with J antennas and built the
slim jim before ever hearing about it, I suspect a lot of people have
done the same. I too noticed a different impedance and a broader match
while making antennas made of TV twinlead

 




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