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11m: > 1/2 lambda: Homebrew high gain vertical antenna.; - Moved to Aerial Homebrew by Staff
Topic Started: 25 Sep 2012 - 21:52 (7,113 Views)
Syborg
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26 Charlie Tango 915

hi folks

when i described my antenna during my intro post a few people were interested in my antenna design so thought id post in on here.
admin please feel free to move this post if ive put it in the wrong section.

basicaly....my main antenna was a 3 section paint roller extension pole measuring about 25ft long, i had a jolly roger flying on it all last summer and when the flag became tatty it came down.

i found an article on iw5edi site about homebrew cb antennas and once i remembered the poles length i set to work.

basicaly i measured and marked out the poles to a full length of 22.5ft and removed all the plastic compression clamps that originaly held the pole at its required length for painting. i hacksawed slots in each sections top to allow for good contact when the jubilee clips clamped the sections together.

this 3 stage pole 22.5ft long was then u bolted to a plank of 2x6 wood right up one end.
then i made a coil using 6ft of twisted copper cable for the matching/tuning device.
this was attached to the main pole via a nut and bolt.

the other end of the coil was bolted through the plank lower down and this is where the outter braid and the 3x 108 inch ground plane wires made of heavy duty earth cable are attatched.

the coax center wire is then connected to the coil in such a way where it can be moved up or down the coil to match the antenna.

the original design has the coil loop once around the antenna rather than a spring like coil.

my wire wasnt rigid enough to hold a horizontal loop so i opted for the spring shape.


i then mounted the whole thing ontop of an 8ft tall steel pipe which is attached to my shed using u bolts through the plank onto the pipe and some large bolts to the shed wall.

the first swr reading was about 3 and couldnt get it lower so i had to lower the twig and shortened it by nearly a ft. the swr was now about 2.

after shifting the driven coax core along the coil i eventualy got it down to around 1.4-1.6.

everything was then soldered into position and sealed using amalgamating tape.


heres a quick pic i took during the making..

the section of pole is obviously only one of the 3 lengths long as unfortunalty 22ft would not fit in my shed,lol

regards.

syborg



the
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Radio Pixie
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26 Charlie Tango 052

Good one Simon. Homebrew antennas is something we can do techanically in an era of sophisticated "black boxes" :)
73 from Dave the Pixie - G7OPC - 26CT052 - 26TM552 - 12m/CB/10m Radioaficionado

Monitoring 70.375 & 145.500 MHz FM


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HomerBB
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2 Charlie Tango 004

Great job!
I really enjoy a home made antenna!
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2CT004/2WR183
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VoG
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HomerBB
26 Sep 2012 - 03:17
I really enjoy a home made antenna!
As long as there's plenty of Mustard
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Nik Gnashers
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26 Charlie Tango 573

OOoooo me likey !

Hmmm, wonder if I can build something similar using the solid core copper wire (that the electricians left at work) slid up the middle of a telescopic fishing rod ..........
:RTFM:
www.WingChunFreestyle.co.uk

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Vortex 3 element yagi - Kenwood TS50s
[imgw=150]http://i481.photobucket.com/albums/rr173/DJ_Nik_Gnashers/dx_code_of_conduct_zps73e84daa.jpg[/imgw]
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Syborg
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26 Charlie Tango 915

Instead of wasting a perfectly good fishing rod why not buy a few meters of White PVC conduit or waste pipe about 1inch in diameter and some blanking caps.
Alot easer to join using solvent weld glue and easier to clamp as it closet to the average sized antenna.

I've heard of alot of vertical dipoles being made using this method with tee connectors.
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Nik Gnashers
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26 Charlie Tango 573

syborg
26 Sep 2012 - 19:18
Instead of wasting a perfectly good fishing rod why not buy a few meters of White PVC conduit or waste pipe about 1inch in diameter and some blanking caps.
Alot easer to join using solvent weld glue and easier to clamp as it closet to the average sized antenna.

I've heard of alot of vertical dipoles being made using this method with tee connectors.
Its not a waste :)

I brought it home from work, half the eyes are broken so its useless for fishing. I'm lucky (in a way), I work for a large charity, so we get allsorts of things donated in everyday. Most of it is broken in some way (unfortunately ppl use us as a dumping ground a lot of the time), so I can have my pick of the unsalable stuff, which can often be used for antenna's :thumb:
www.WingChunFreestyle.co.uk

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Vortex 3 element yagi - Kenwood TS50s
[imgw=150]http://i481.photobucket.com/albums/rr173/DJ_Nik_Gnashers/dx_code_of_conduct_zps73e84daa.jpg[/imgw]
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HomerBB
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2 Charlie Tango 004

Nik Gnashers
26 Sep 2012 - 18:19
OOoooo me likey !

Hmmm, wonder if I can build something similar using the solid core copper wire (that the electricians left at work) slid up the middle of a telescopic fishing rod ..........
:RTFM:
That is exactly how this 1/4 wave GP was made.

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2CT004/2WR183
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Syborg
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26 Charlie Tango 915

looks like a thunderpole from the old days!!!

heres a pic of the high gain erected and a 1/4 wave dipole i made using a modified magmount and some earth cable.....
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HomerBB
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2 Charlie Tango 004

Now that was ambitious. Some folks just never try and others go ahead and take a chance.

Tell us, how is the SWR, and how is it doing for you?
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2CT004/2WR183
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Syborg
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26 Charlie Tango 915

the swr on the dipole is 1.3-1.5
and the swr on the high gain is a shade over 1.4 on all channels.


The dipole is made of 2 lengths of 5mm earth cable cut to 108 inches long and i simply left about 4 inches each end free to fold back
to get the swr within a reasonable range,

The dipole is running from my commtron cb40f rig running on low power with a guitar effects pedal for the echo just for local cb and the high gain twig is running on my major 588 multi.


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Edited by Syborg, 2 Oct 2012 - 18:29.
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HomerBB
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2 Charlie Tango 004

Not bad at all. I like them both.
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2CT004/2WR183
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Nik Gnashers
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26 Charlie Tango 573

Me too !

I am very interested in learning how to make a matching coil for a 1/2 wave vertical, thinking about building my own antron99 from wire and a fishing rod :thumb:
www.WingChunFreestyle.co.uk

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Vortex 3 element yagi - Kenwood TS50s
[imgw=150]http://i481.photobucket.com/albums/rr173/DJ_Nik_Gnashers/dx_code_of_conduct_zps73e84daa.jpg[/imgw]
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HomerBB
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2 Charlie Tango 004

Nik, for and end fed 1/2 wave like the A99 you'll need 2 components fed parallel with each other.
They are a capacitor, and an inductor (coil). The bottom of your capacitor and you coil are attached to the braid of your coax, and the top of the coil and cap are feeding the vertical radiator (or horizontal if you lay it over). The coax center taps the coil for a match.
If you build a sliding capacitor like mine you will find the lowest possible SWR with both the components, then work the capacitor as low as it will go, then fine tune the antenna with the coil tap. If it doesn't behave, make an adjustment to the length of the radiator. If you are using tubing the radiator ought to be around 17.5' long.

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Edited by HomerBB, 2 Oct 2012 - 22:26.
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2CT004/2WR183
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HomerBB
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2 Charlie Tango 004

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Syborg
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26 Charlie Tango 915

That is awesome!!! I didn't realise you could make a horizontal end fed twig!!
Love the matching device, a lot better than my birds nest lol.
In my defence it was a first attempt at a half decentish twig built from junk.
The other half was not too happy when I raised this monstrosity lol.
The dipole was a slightly softer blow as it kind of blends in with the surrounding washing lines,lol

I'm now entering the mental state of constructing a 2 element yagi, I'm thinking of keeping it cheap and rotating the mast by hand through a small hatch in the shed wall.

Something to keep the mind whiring for a bit.


Regards


26ct915
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Nik Gnashers
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26 Charlie Tango 573

Charles :
Many thanks for the info, I did read your old thread which contains the same pictures earlier mate.
Tonight, a good friend gave me an old broken half wave silver rod antenna. I broke apart the bottom bit, and all that was inside, was a small coil of thin copper wire, the centre of the so239 was attatched 3 turns up, and the braid connected to the end. The other end of the coil was connected to the bottom of the main vertical aluminium pole.
I tried to re-use the coil, but it was corroded and brittle, and broke, so I used some slightly thicker copper wire and copied the coil and tap position.

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I have no idea if this will work, but would welcome any advice. I would build and add a capacitor if needed, but the antenna I stripped did not have anything else just a small coil ?
I really REALLY want to understand the matching device, and build a 1/2 wave end fed vertical, although I don't own (and cannot afford to buy at the moment) an antenna anyliser, I only have an swr meter.
Any help greatly appreciated, and if you could add anything Charles from previous experience and what I have started to build (pic above) I would be very grateful for any comments or help.
Many thanks,
Nik

EDIT : The top element of this antenna is going to be the same diameter copper wire as the coil, inside a glass fibre fishing pole.
Edited by Nik Gnashers, 3 Oct 2012 - 20:19.
www.WingChunFreestyle.co.uk

Posted Image
Vortex 3 element yagi - Kenwood TS50s
[imgw=150]http://i481.photobucket.com/albums/rr173/DJ_Nik_Gnashers/dx_code_of_conduct_zps73e84daa.jpg[/imgw]
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HomerBB
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2 Charlie Tango 004

syborg
3 Oct 2012 - 20:17
That is awesome!!! I didn't realise you could make a horizontal end fed twig!!
Love the matching device, a lot better than my birds nest lol.
In my defence it was a first attempt at a half decentish twig built from junk.
The other half was not too happy when I raised this monstrosity lol.
The dipole was a slightly softer blow as it kind of blends in with the surrounding washing lines,lol

I'm now entering the mental state of constructing a 2 element yagi, I'm thinking of keeping it cheap and rotating the mast by hand through a small hatch in the shed wall.

Something to keep the mind whiring for a bit.


Regards


26ct915
Your work is fine. Believe me, I've been doing these things over and over again so they get a bit neater each time.

Yes, they work on their side. I gave this same antenna to a friend when he visited last week. He has it hanging horizontal outside his residence and is talking DX with it everyday!

For a very small Yagi look at my Made A Moxon thread, or other Moxon threads on the forum.
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2CT004/2WR183
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HomerBB
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2 Charlie Tango 004

Nik,
First of all, in your place I'd proceed with trying to do it without the capacitor. I tried it and got nowhere. I found information on the matching network I used and succeeded. Perhaps your experience will teach us both something.

Also, about your coil. Try to keep all of your coil wraps evenly spaced and uniform in size. It is optimum to have the spaces as near the distance apart as the diameter of the wire you are using. It may not be possible, but try.

One way to achieve this spacing is to use a cord or window screen spline between each wrap of the wire as you coil it around a broom handles or something of the proper diameter. Once it is wound the number of turns you need use some hot glue in several places to keep the coil a unit. When it cools, pull it off the broom stick and cut away the spacer material. I used a wooden dowel covered with wax paper, and strips of this hose to do this.

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A 5/8 wave antenna does not need the capacitor at all, but a good set of radials are in order.

You may get a way with pre-tapping the coil before you assemble and mount the antenna, but usually you will have to find the sweet spot for the match afterwards. slight differences in coil size, spacing, the antenna materials types, and environment can make each antenna tune slightly differently.

Make a thread and keep us posted with photos.
Edited by HomerBB, 3 Oct 2012 - 22:15.
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2CT004/2WR183
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Syborg
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26 Charlie Tango 915

Just out of curiosity, how come a 5/8 twig need radials but most silver rod half wave don't ?

Regards

26ct915
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