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 G0KSC Antenna Query 
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Post G0KSC Antenna Query
Hello,

I have sourced a 2nd hand Innovanntennas 8el LFA. I think its an old one, I have disassembled and cleaned it up and its just about ready to go up, its looking nearly new now.

Can anyone tell me if I need a choke balun on it at the feed point?

Additionally, does anyone know what this "arm" does that connects the driven LFA element to the boom?

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Thanks!


Thu Dec 07, 2017 12:17 am
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
The bar is a 1/4 wave matching stub, Pawsey stub it's called,

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Thu Dec 07, 2017 3:22 am
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 G0KSC Antenna Query 
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Thanks, I assume that this will mean that not (ugly) balun or choke is required?


Thu Dec 07, 2017 11:11 am
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
Personally never needed a choke balun at these frequencies/antenna types.

If the cats hair stands on end when you key up, fit one

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Thu Dec 07, 2017 11:17 am
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 G0KSC Antenna Query 
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Haha thank you.


Thu Dec 07, 2017 11:45 am
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
From Justin's website.

Pawsey Stub

19/11/2010 Many Hams have seen inconsistencies with the Pawsey stub, largely believed to be due to the varied velocity factor seen in most coax cables. Steve, G3TXQ contacted me with a very interesting viewpoint and provided some seemingly valid information explaining why only coax of the same type should be used for the Pawsey stub, not a separate, dissimilar wire. I therefore would no longer recommend this style of Pawsey stub but will keep the information here. My antenna balun with a feedpoint choke may give the best, all round performance: http://www.hamradio.me/antennas/coax-ve ... #more-1528

Cheers

Tony

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Thu Dec 07, 2017 12:58 pm
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
I did see that earlier today, thank you.

I could remove it altogether and use a coax choke - will leave enough coax to allow.


Thu Dec 07, 2017 4:02 pm
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
Thanks for everyone help on this.

For those that might be interested. I disassembled the antenna completely, cleaned it up thoroughly, made up a new N-type tail, reassassembled and installed on the mast in place of a 9el Tonna. It came up well and performs very well also. Pardon the state of my garage/workshop, it needs a good tidy up but I am too busy doing other more interesting things!

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Fri Dec 29, 2017 10:29 am
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
Well done on getting it sorted and up in the air, hope you catch some good openings in the new year :good:

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Fri Dec 29, 2017 11:02 am
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
Many thanks, yes that would be good.

I am also in the process of building my own 8el LFA as this is something I have been meaning to do for a while (but this second hand one came up first).


Fri Dec 29, 2017 11:20 am
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
Excellent. Use the bits to make a 70cm LFA then?

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Fri Dec 29, 2017 1:07 pm
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 G0KSC Antenna Query 
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Post Re: G0KSC Antenna Query
just to add to this thread. i recently altered my old 9el LFA, removed the pawsey stub and added an aluminium stauff clamp onto the boom opposite the feed point. i have tried a couple of different balun methods, one being a 1/4 wave pawsey stub on the coaxial input. this did not work as intended and i could not find a suitable dip in swr and impedance near to 50 ohm. i have found that I0QM's 1/4 wave with 3/4 wave coaxial did help things dramatically when it came to a resonant point.

now im not sure if i over engineered things and have debated if a few turns of coax into a choke would have the same effect if not better. also i have considered clamping ferrites over the coax which is a method justin now appears to use.

i can confirm that the aluminium stauff did seem to do its DC grounding job and noise levels have improved.

does anyone have any thoughts to add to this?

Cheers Phil DGP

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Thu Apr 26, 2018 1:00 pm
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