J pole for scanning?

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J pole for scanning?

Postby Kayos » Sat Dec 31, 2016 5:01 pm

While googling for antenna ideas I keep coming across the J pole, made out of copper pipe
Could I make one for scanning, say use the middle airband freq in the calculations?
My main reason for wanting to try it is that it will cost me £0, I will have all the bits in my van and a mounting pole already on the side of the house
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Re: J pole for scanning?

Postby m0lsx » Sat Dec 31, 2016 5:35 pm

A J pole makes a perfectly reasonable scanning antenna.
The J Pole is a slight variation on the HF Zepp Antenna & Slim Jims/folded diples are slight variations on that.
Two designs I have used are similar to those below..


Image


Image



On the ladder line antenna above take care of velocity factors. As the Velocity Factor will effect measurements.
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Re: J pole for scanning?

Postby Chris P » Sun Jan 01, 2017 7:38 am

A true J pole has a feed point slightly above the bottom of the J , I have a slimjim ( set up for 126Mhz)in the loft which is better on some frequencies than my D777 mounted above the roof , probably due to the lower angle of "radiation " that the slim jim exhibits compared to the D777 collinear .There was at one time a calculator for slim jim dimensions on a web site belonging to John M0UKD which I found to be helpful I will check to see if the website is still active


Edit the website is still active and a slim jim calculator can be found with one click put "slim jim calculator" into your search engine and you should be directed to Johns website
Regards Chris aka G8FFF nipper or tazmin88
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Re: J pole for scanning?

Postby essexRXer » Sun Jan 01, 2017 10:24 am

Thanks for posting the above, Slightly off topic but- I have been experimenting with all types of antennae, would a Magmount with a folded bracket mounted to the correct dimensions to follow the whip in parallel like a J-pole be any better than a biscuit tin?

On everything I have tinkered with so far, I discover that a coat hangar bent to duplicate exactly my shop purchased el-cheapo dual band twig has performed the best for the bands I monitor. :rolleyes:
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Re: J pole for scanning?

Postby Kayos » Sun Jan 01, 2017 4:40 pm

I have built a J pole based on the link posted above, middle of airband is 122.5 so i put that into the calculator
I did add a mounting leg as per another calculator i found online.
My method of attaching the coax will need improving, i used self tappers and crimp on forks, im thinking bonding clamps would be good as they are purpose designed to join cable to pipes

It is an improvement over the dipole on airband, LBA ATIS is very faint with squelch on 1 on the dipole, but much clearer, with some interference with the J pole and the squelch on 2.

I made it from 15mm copper as i havent got any 22 pipe, its currently strapped to an old tripod and poking out of the Velux in the loft...
If I do decide to mount it externally i used tee's instead of elbows and left both ends open as I don't have any cap ends either

I did find a length of 28mm copper, would the extra diameter be any benefit?

Im also looking at making a small one as per m0slx with an N type chassis plug and a BNC to N adapter, but i need some suitable copper wire
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Re: J pole for scanning?

Postby Kayos » Mon Jan 02, 2017 1:49 pm

Some pictures attached

ImageJ Pole-1 by Stuart Burrows, on Flickr

ImageJ Pole-2 by Stuart Burrows, on Flickr

ImageJ Pole-3 by Stuart Burrows, on Flickr

Im going to make another to mount outside, with an n connector on the bottom for neatness
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Re: J pole for scanning?

Postby scan_8051 » Mon Jan 02, 2017 4:06 pm

nice antenne Kayos, I found this on the internet.

http://nt1k.com/blog/2011/open-stub-j-p ... any-times/

Maybe I will build one.
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