11m: 1/4 wave groundplane base antenna build

Joined: July 9th, 2011, 4:48 pm

September 27th, 2012, 6:39 pm #1

Early days of the build, but I am making a quarter wave groundplane antenna for my home qth. This will replace the sirio sd27 dipole I have up, which I cannot swr down below 2.1. The sd27 works ok, but as ever, I like to experiment and try home-brew twigs, so fingers crossed this will out perform the vertically mounted dipole.
Ingredients :
1) approx 20 feet of solid core copper mains electrical cable (free left by electrician at work).
2) the bracket for the sd27 dipole, which mounts it to a vertical mast (free thanks to a good friend).
3) a telescopic glass fibre fishing rod (free donated at work some of the eyes were broken).
4) a dipole centre with so239 socket (£5.95 from knights).

Took the metal eyes off the fishing pole, stripped the outer plastic insulator from the mains cable and cut FOUR lengths of 103" each.
Mounted the dipole centre to the sirio bracket.

The intention is to run the upper 1/4 wave wire element up the inside of the fishing rod, and secure it at the top with something yet to be decided, and connect the other end to the dipole centre. Then connect the three groundplane wires to the other connection on the dipole centre and suspend these out at 45 degrees similar to a skylab / thunderpole II & III / Starduster.


Last edited by Nik Gnashers on October 14th, 2013, 3:23 pm, edited 1 time in total.
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Joined: January 16th, 2011, 9:03 pm

September 27th, 2012, 6:52 pm #2

Nice one Nik..

Looking forward to seeing it progress :thumb:
Last edited by Cozzmik on September 27th, 2012, 6:52 pm, edited 1 time in total.








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Joined: January 8th, 2010, 2:50 am

September 27th, 2012, 9:00 pm #3

It's looking like a great start!!



2CT004/2WR183
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Joined: July 9th, 2011, 4:48 pm

September 28th, 2012, 3:51 pm #4

Last night, I thought about the U-Clamps holding the fishing pole, and realised that when tightened, they might crush the pole itself.
So, today I salvaged a couple of old dumbbell plastic handles, to fit around the outside of the pole, and tried to find some plastic hollow pipe with a 25mm outer diameter to slide inside.
Looked all over, nothing would fit, so I had to BUY something (boooo grrrrrr etc). In the end, the cheapest thing was a 'bottom entry overflow connector' from wickes (sounds painful !). This brings my build costs spiralling up, it was £2.45.
So added to the £5.95 for the dipole centre, its standing me at £8.40 so far.
Anyhow, after chopping the screw threads off the ends, and inserting it into the pole, adding the dumbbell handles, its very very strong, and I can tighten up the U-Clamps and have faith that it will not start to crack in the wind :thumb:



EDIT : I like the way you have suspended the ends of your wire groundplanes Charles !
Very clever indeed ......
Last edited by Nik Gnashers on September 28th, 2012, 3:55 pm, edited 3 times in total.
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Joined: July 9th, 2011, 4:48 pm

September 29th, 2012, 1:19 pm #5

Today I managed to finish and erect the antenna.
I connected the groundplane wires and tested it, by bolting it to a wheelie bin handle, trimmed about 2" off the main element (so the finished length is approx 101").
I didnt trim the groundplane wires, they are 103". My SWR readings were 1.1:1 on ch1 ukFM, and 1.1:3 on ch40 ukFM.
Put the supporting pole on, by drilling through it, and bolting it to the wall bracket, to stop it twisting in the wind.



Next up, I secured the top of the main vertical element wire (which pokes out the end of the fishing rod) with a block connector to stop it falling inside the rod, and amalagated the top to stop water getting in. The rod sections are also amalgamated.
I mounted the antenna onto the pole, tightened everything up and it seems very secure.
I checked SWR, and as expected, it rose slightly, it reading 1.1:4 on ch1 ukFM, and 1.1:6 on ch40 ukFM. I knew it would be higher because the shed roof which is directly under the antenna, has steel mesh reinforcement inside the concrete which is obviously affecting the antenna and groundwires especially.
Its a lot better than the sirio sd27 dipole though !!!
Had a signal check from a station 15 miles away. Old reading on the dipole was 1 and a half 'S' points and radio 3 audio. New reading a solid 4 'S' points and nice radio 4 to 5 !!!! So an improvement of 2 and a half 'S' points over the sirio sd27 dipole mounted at exactly the same height in the same position.



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All CT members are expected to use good operating procedure, good manners, and be friendly...Please do not chat on any calling frequencies, or use bad language on air, thank you it is appreciated.
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Joined: January 16th, 2011, 9:03 pm

September 29th, 2012, 2:26 pm #6

:clap: Stealthy lil antenna you`ve made there Nik.....

With the way conditions are at present im sure you can have some nice contacts on that now your back on the air homebase... :thumb:
Last edited by Cozzmik on September 29th, 2012, 2:27 pm, edited 2 times in total.








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Joined: January 8th, 2010, 2:50 am

September 29th, 2012, 3:07 pm #7

Beautifully done.
Very sharp indeed, and not surprising that adding radials would result in an improvement to your performance.

Listen for me on 27.385 LSB.


2CT004/2WR183
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Joined: June 23rd, 2009, 10:44 pm

September 29th, 2012, 10:06 pm #8

Nice job Nik - you should do well on that :thumb:

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Joined: July 9th, 2011, 4:48 pm

October 14th, 2017, 6:42 am #9

Images now uploaded to a new host !!!!

[imgw=700]https://i.imgur.com/cHu43ye.jpg[/imgw]


[imgw=700]https://i.imgur.com/P7b0tIf.jpg[/imgw]


[imgw=700]https://i.imgur.com/FP3Hdp9.jpg[/imgw]


[imgw=700]https://i.imgur.com/RO1jLVC.jpg[/imgw]


[imgw=700]https://i.imgur.com/qfvRDK9.jpg[/imgw]
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All CT members are expected to use good operating procedure, good manners, and be friendly...Please do not chat on any calling frequencies, or use bad language on air, thank you it is appreciated.
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Joined: January 29th, 2017, 11:40 am

May 4th, 2018, 4:08 pm #10

Hi everyone,
After building various antennas with mixed results, I decided to build a version of Nik Gnasher's 1/4 wave (pictured)
Pleased to report my first overseas dx contact in Northern Italy!! Well-happy :D

I built mine with 3 groundplanes, with the vertical being a simple piece of 106" #18 gauge copper wire inside a fibreglass tent pole.

Thanks again to Nik for this idea and pics.

Kev. :rock:
IMAG1620.jpg
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