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Old February 9th 07, 12:06 PM posted to rec.radio.amateur.antenna
Ian Jackson Ian Jackson is offline
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First recorded activity by RadioBanter: Oct 2006
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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.
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