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[ 12 posts ] |
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M6MVW
Advanced Member
Joined: Mon Feb 13, 2017 3:18 pm Posts: 429 Location: Chelmsford, Essex
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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? Attachment:
8elLFA3.jpg [ 88.41 KiB | Viewed 1925 times ]
Thanks!
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Thu Dec 07, 2017 12:17 am |
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ei2glb
Advanced Member
Joined: Thu Jul 26, 2007 3:39 pm Posts: 3027 Location: Kildare IO63MD
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Re: G0KSC Antenna Query
The bar is a 1/4 wave matching stub, Pawsey stub it's called,
_________________ Trevor EI2GLB QRZ+LOG WX
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Thu Dec 07, 2017 3:22 am |
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M6MVW
Advanced Member
Joined: Mon Feb 13, 2017 3:18 pm Posts: 429 Location: Chelmsford, Essex
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Re: G0KSC Antenna Query
Thanks, I assume that this will mean that not (ugly) balun or choke is required?
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Thu Dec 07, 2017 11:11 am |
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G4WLI
Advanced Member
Joined: Sat Jan 19, 2013 12:30 pm Posts: 1171 Location: Manchester
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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
_________________ G4WLI (G8IKW) Peter Education officer, West Manchester radio Club http://www.wmrc.co.uk/
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Thu Dec 07, 2017 11:17 am |
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M6MVW
Advanced Member
Joined: Mon Feb 13, 2017 3:18 pm Posts: 429 Location: Chelmsford, Essex
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Re: G0KSC Antenna Query
Haha thank you.
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Thu Dec 07, 2017 11:45 am |
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gw8asd
Moderator
Joined: Fri Jul 20, 2007 1:02 pm Posts: 15909 Location: IO83lb, Wrexham
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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-1528Cheers Tony
_________________ 50MHz and above from IO83lb
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Thu Dec 07, 2017 12:58 pm |
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M6MVW
Advanced Member
Joined: Mon Feb 13, 2017 3:18 pm Posts: 429 Location: Chelmsford, Essex
Feedback: 39 (100%)
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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.
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Thu Dec 07, 2017 4:02 pm |
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M6MVW
Advanced Member
Joined: Mon Feb 13, 2017 3:18 pm Posts: 429 Location: Chelmsford, Essex
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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! Attachment:
IMG_20171206_203139.jpg [ 95.73 KiB | Viewed 1737 times ]
Attachment:
IMG_20171206_203146.jpg [ 83.43 KiB | Viewed 1737 times ]
Attachment:
IMG_20171222_160020.jpg [ 49.46 KiB | Viewed 1737 times ]
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Fri Dec 29, 2017 10:29 am |
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F4VPC
Advanced Member
Joined: Mon Oct 19, 2009 8:22 pm Posts: 1286 Location: Monteneuf - Brittany IN87VV
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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
_________________ Kelvin F4VPC / GW4TTU, feeling a bit like Bonnie Tyler - Lost in France !
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Fri Dec 29, 2017 11:02 am |
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M6MVW
Advanced Member
Joined: Mon Feb 13, 2017 3:18 pm Posts: 429 Location: Chelmsford, Essex
Feedback: 39 (100%)
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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).
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Fri Dec 29, 2017 11:20 am |
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GD1MIP
Contributor 2023
Joined: Fri Feb 20, 2009 11:43 pm Posts: 2309 Location: Mwyljyn Moddey, Ellan Vannin. IO74ti
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Re: G0KSC Antenna Query
Excellent. Use the bits to make a 70cm LFA then?
_________________ Andy - GD1MIP Using decidedly average equipment from Mwyljyn Moddey, Ellan Vannin or IO74ti to you and I.
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Fri Dec 29, 2017 1:07 pm |
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2E0DGP
Advanced Member
Joined: Thu Aug 25, 2011 10:09 am Posts: 523 Location: Chorley - IO83QP
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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
_________________ Phil SRZ
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Thu Apr 26, 2018 1:00 pm |
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