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 Slim Jim Antenna.

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soulboy
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Slim Jim Antenna. Empty
PostSubject: Slim Jim Antenna.   Slim Jim Antenna. Icon_minitimeFri May 21, 2021 11:01 pm

Hi.
Has anyone ever tried to build a 27/28 Mhz 'Slim Jim' style antenna ?
I have built successful models for 2M & 70 cms but 27/28 eludes me.
I tried to follow a version from an old practical wireless magazine article and built it out of 22mm and 15mm copper tube. It was big...but it was way off frequency, resonant around 40 mhz.
Any thoughts ?
Cheers,
Soulboy

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Hotel Zulu 253
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Slim Jim Antenna. Empty
PostSubject: Re: Slim Jim Antenna.   Slim Jim Antenna. Icon_minitimeSat May 22, 2021 1:30 am

Slim Jim Antenna. Images11

Was your slim Jim built like this ?

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Victor
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PostSubject: Re: Slim Jim Antenna.   Slim Jim Antenna. Icon_minitimeSat May 22, 2021 6:15 am

Hi David,

You have made this posting twice on the forum so to avoid any confusion and adhere to the forum rules I have removed the duplicate. I understand that you may have been unsure of where to post your query hence the cross-posting so as admin I am here simply to try and help out. 


Anyway, speaking of trying to help....

I came across some resources a while back myself when first looking at a 'Slim Jim' antenna after being suggested to try one for VHF. I will see if I can find them out for you and will post here accordingly.


All the best,
Victor
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Victor
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Slim Jim Antenna. Empty
PostSubject: Re: Slim Jim Antenna.   Slim Jim Antenna. Icon_minitimeSat May 22, 2021 7:40 am

Hi again David,

I remembered that there was no advantage in a 'Slim-Jim' compared to a 'J-Pole' and the following link will provide some detail as to why :-

https://www.hamradio.me/antennas/slimjim-vs-traditional-j-pole-antenna.html


I can understand that those building typical VHF examples will be utilising twin-line feeder and it may seem more advantageous to simply clip out/short together sections than removing whole swathes of the feeder. As there seems to be no real advantage or disadvantage to either it's obvious the easier path will be taken with such feed line constructions.

However, if building the antenna from other resources such as copper pipe it would be more advantageous to leave out the hassle and expense of adding the fold back of the 'Slim-Jim' sections especially if it adds nothing useful to the final construction.

There are those that will argue a Slim-Jim will somehow outperform a J-Pole despite evidence to the contrary and you have to make sure that their view isn't a vested interest. Those that sell them will obviously swear their advantages as well as those that have gone to the expense and efforts of building them. Some are in it for the profit and none of us like to feel like a fool.


I couldn't find a reference to a Practical Wireless example but can give you a link to an article from the venerable L.B. Cebik who describes one for 10m :-

http://on5au.be/content/a10/ant41.html

If I come across anything of help I'll be sure to post it up for you.


In my own experience I didn't build a VHF Slim-Jim as the once cheap and plentiful twin line feeder now attracts awfully knocked up prices. After discovering that it added no benefit to the final antenna I constructed a J-Pole simply from wire and sure enough it worked. It didn't however provide anything more than the simple wire dipole arrangement performance wise. The only advantage I could see was that it was an end fed arrangement but it was far more sensitive to it's environment than the dipole ever was.

My 'walk-away' experience from that was to stick with simple dipoles including on HF frequencies never being able to contemplate or justify the hassle/expense of such arrangements on a bigger scale.

Experiences and opinions may vary. Wink


Others may have more to add, maybe questions on 'velocity factor', your pipe diameters, etc. etc. Part of the 'fun' in such ventures can be in wading through the quagmire of 'information' in the hope you get successfully to the other side. Often it's simply just 'fun' being involved in something that takes our interest and fills our time....who am I to argue with that?

I hope you get somewhere with it all, despite the frustrations that can often occur. (40MHz???)


All the best,
Victor

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PostSubject: Re: Slim Jim Antenna.   Slim Jim Antenna. Icon_minitimeSun May 23, 2021 5:22 pm

Hi Victor and Zulu 253.
Firstly, many thanks Victor for your input, some good stuff to read through.
Also appologies for posting it twice, still learning how the site works.

Secondly, to Zulu 253, yes, that's the one. Its very tall when made for 27/28. M0 UKD posts some decent stuff.

It was built but could not get it to resonate anywhere near 10 or 11m, today I dismantled
it. I have got the local planning officer on my back over the main antenna at home. The slim Jim was laid down in the garden whilst being constructed, but yet it was still mentioned in the letter from the council...

I think the next attempt at the slim Jim, or maybe the J pole, will be made from wire on a timber post, or maybe if funds permit a DX commander telescopic mast.

Cheers everyone.

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Slim Jim Antenna. Empty
PostSubject: Re: Slim Jim Antenna.   Slim Jim Antenna. Icon_minitimeSun May 23, 2021 7:17 pm

Hi David,

No worries, I'm simply here to help out where I can.


Sorry to hear of your 'planning officer' woes, they should only concern themselves with offering advice and only rely on enforcement where required. It may be worth reading up a bit on planning law regarding 'roof line' and 'temporary structures' as well as antenna design. Wink

I wish you well with your continued antenna experiments. Slim Jim Antenna. 1f44d 


All the best,
Victor
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PostSubject: Re: Slim Jim Antenna.   Slim Jim Antenna. Icon_minitimeMon May 24, 2021 2:13 pm

Hi David, 

Sorry to jump in I just wanted to let you know if you are making the next version from coax/wire the Sotabeams 10m Pole is cheaper than the DX Commander pole at £35. I don’t think the sota one is as sturdy as the DXC but I have used one for over 6 years now with a T2LT on the hilltops with no problems whatsoever, I did remove the Top section though as it is too thin to be of use. It might be a viable option for you anyway. Take care and happy experimenting. 

https://www.sotabeams.co.uk/telescopic-masts-sotapoles-7m-and-10m/

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