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 Looking for ideas - Homebrew portable verical for 15m 
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Post Looking for ideas - Homebrew portable verical for 15m
I am lucky enough to live very close to several beaches here on the north west coast of Ireland. Unfortunately with our weather they are mostly empty however I have been reading about the benifits of salt water for lowering take off angles for DX and this past weekend I found a great spot where I was able to drive right down to the waters edge on the sand and worked some great DX from the car on 15m with a cheap Multiranger antenna on a tri-mag and 100w.... So I was wondering about homebrewing a vertical for 15m that would be easy to set up and dismantle and that I can throw in the car... I'm trying to decide between a 1/4 wave and a vertical dipole using the usual wire and plastic poles etc... If I went with a ground plane which would be set up right next to or almost in the salt water, what would the best solution be for radials, elevated off the ground or spread out on the sand?... how many would I need depending on the installation?... Then for a vetical dipole I was looking at the iPro type of idea using capacity hats to shorten the overall height of the aerial... again using wire and maybe plastic electrical conduit?

Any ideas much appreciated...

EI2HPB Dave


Mon Feb 18, 2013 7:42 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
Dave,

For simplicity, how about a vertical half-wave dipole using the "mixed mode" feed arrangement to put the feedpoint at the bottom? 23ft long fishing pole with some coax fed up it. No radials needed. Over salt water, with the bottom 1ft above the water, it has a main lobe at about 8 degrees elevation.

73,
Steve G3TXQ


Mon Feb 18, 2013 7:57 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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I think for single band operation you can't beat 's suggestion, I have a feeling you're going to be very happy with the results ;)

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Mon Feb 18, 2013 8:40 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
i still need to make one of those , got the 174 i was going to use and the cores for the choke ..

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Mon Feb 18, 2013 9:22 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
G3TXQ wrote:
Dave,

For simplicity, how about a vertical half-wave dipole using the "mixed mode" feed arrangement to put the feedpoint at the bottom? 23ft long fishing pole with some coax fed up it. No radials needed. Over salt water, with the bottom 1ft above the water, it has a main lobe at about 8 degrees elevation.

73,
Steve G3TXQ


Steve

Sounds good... can you explain how the mixed mode feed works in more detail... I'm not familiar with the concept... (please make it very simple... lol)

many thanks

Dave


Mon Feb 18, 2013 9:36 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
I'll have a go:

Image

Fig 1: a conventional wire dipole A+B fed with coax C
Fig 2: make dipole leg A a tube
Fig 3: take coax C and feed it through dipole leg A

It's still a centre-fed dipole, but now the feedline comes in from one end.

Fig 4: take away the tube forming leg A and replace it with the outside surface of coax C; to do this we place a choke where we want dipole leg A to "finish".

Takes longer to describe than make :)

Here's a reference to a practical construction article:
http://www.worldradiomagazine.com/wro_i ... _14-29.pdf

So basically you have a length of coax with the braid stripped from the far end by a quarter-wavelength, and you place a good choke a half-wavelength from the far end.

Hope that's clear,
Steve G3TXQ


Mon Feb 18, 2013 10:42 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
Why RG174 rather than cheap and cheerful RG58, is it down to the braid or dielectric thanking you please? :blush:

Also would a toroid from your chart be adequate Steve, especially if it was blasted with say 300 watts?

Cheers, Dave.


Tue Feb 19, 2013 9:37 am
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
Because RG174 is cheap and light for portable operation; but you could just as easily use RG58.

10 turns of RG58 on a FT240-61 core would be good for 15m.

73,
Steve G3TXQ


Tue Feb 19, 2013 10:01 am
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
Thanks Steve, having seen Billys reference to RG174 I thought I was maybe missing something.

Cheers, Dave.


Tue Feb 19, 2013 12:21 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
Dave , sorry about that , like steve says also i just happen to have some spare which would be better suited to that antenna than using it here at home as a tranny line .. every ounce loss counts as i'm very lazy in my old age :) .. going to make the 40m version so all in all my homebrew qrp set up will total less than about 1.5 lb tops ..in fact the 60 odd footish antenna will probably weigh more than the rig/key and power source :)

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Tue Feb 19, 2013 1:20 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
G3TXQ wrote:
So basically you have a length of coax with the braid stripped from the far end by a quarter-wavelength, and you place a good choke a half-wavelength from the far end.


Steve

Please bear with me as I can be a bit thick... loll ... and I must admit I've never heard of or used this approach before... so for the 15M dipole I need to cut a half wave length of RG58 coax (can I use RG 213 as I might have some spare?).... run that along a 23ft fishing pole or fibre glass push up job... strip the coax back to the half way mark and use the braid to double back down the pole and form the bottom half of the antenna... finally add a choke of RG58 at the feed point and connect a run of coax back to the radio... have I got it correct or am I missing anything?... and thanks for your patience hi hi...

many thanks

Dave EI2HPB


Tue Feb 19, 2013 8:58 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
irishdx wrote:

Steve

Please bear with me as I can be a bit thick... loll ... and I must admit I've never heard of or used this approach before... so for the 15M dipole I need to cut a half wave length of RG58 coax (can I use RG 213 as I might have some spare?).... run that along a 23ft fishing pole or fibre glass push up job... strip the coax back to the half way mark and use the braid to double back down the pole and form the bottom half of the antenna... finally add a choke of RG58 at the feed point and connect a run of coax back to the radio... have I got it correct or am I missing anything?... and thanks for your patience hi hi...

many thanks

Dave EI2HPB


You can do it that way, but it's wasteful. The upper half of the dipole can be any piece of wire, only the lower half has to be coax, additionally there's no need to fold the screen back on itself, the screen is capable of carrying current on the inside, and on the outside, it's the choke that stops the outside of the screen carrying current back to the rig and enables you to create the other leg of the dipole.

RG213 just increases the weight, but will work just the same

Hope that makes sense

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Tue Feb 19, 2013 9:16 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
I wouldn't use RG213 - it's a bit thick and doesn't really offer any advantage.

1) Take a length of RG58 - for 15m operation make sure it's comfortably longer than 24ft.
2) Strip the outer jacket and the braid for a distance of 11ft from one end - throw it away!
3) Wind a choke comprising 10turns of the RG58 on an FT240-61 core, starting at a point 22ft from the end you stripped.
4) What's left of the RG58 on the other side of the choke is your feedline. You can make it as long as you need to reach the radio - the critical thing is to position the choke 22ft from the stripped end.
5) Tune it by trimming the stripped end.

Or as G7DIE says you could replace the 11ft stripped section with any old wire; but stripping the coax means you don't have a join :good:

Hope that helps.
Steve G3TXQ


Tue Feb 19, 2013 9:20 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
All understood and many thanks chaps... I cant wait to try it out now... I have a cracked and battered old fibreglass mast but it will do for testing purposes... the most expensive thing is the FT240-61 core, because I'm in limbo land out here I'll have to buy it on ebay and it looks like costing about 20 quid when the postage is added :cry: Is there anywhere cheaper selling these?

Dave EI2HPB


Tue Feb 19, 2013 10:23 pm
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 Looking for ideas - Homebrew portable verical for 15m 
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Post Re: Looking for ideas - Homebrew portable verical for 15m
£14.75 + £1.90 p&p here:
http://www.ebay.co.uk/itm/NEW-FT240-61- ... 3a7e722fac

However, Amtools sell various other size #61 cores much more cheaply; if I get a chance tomorrow I'll look at winding details for an alternative core (or cores) that would be cheaper. That's if you can wait ;)

Steve G3TXQ


Tue Feb 19, 2013 10:35 pm
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