Hi-Gain Vertical Half Wave Antenna

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Re: Hi-Gain Vertical Half Wave Antenna

Post by sharky » Thu Feb 05, 2015 9:05 pm

Maximus wrote:A 50w version melted/snapped in half after putting 180w through it.

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Woooooooooow :rip
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Re: Hi-Gain Vertical Half Wave Antenna

Post by DannyRWD » Sat Feb 07, 2015 11:34 pm

I still own one its at my mums ill try dig mine out! Always wanted to copy it might stand half a chance with the schematic posted

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Maximus » Mon Feb 09, 2015 6:31 am

Lucky git. I tried to repair mine and the thing was glued together fairly strong. The worst part was it was I bought it just before NRG closed and hadn't used it for over a year. It was immaculate, now it's scattered in pieces somewhere in the garage.

Ended up sticking up a dipole as was in a rush to get back on air and everyone were complaining that they were stuck with listening to Radio 1 lol

Now I live abroad, I'm looking for a replacement. Perhaps the local folks in electronics town may be able to help. They're very good at building 2m and the 245mhz cb aerials.
DannyRWD wrote:I still own one its at my mums ill try dig mine out! Always wanted to copy it might stand half a chance with the schematic posted

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Maximus » Mon Feb 09, 2015 6:44 am

The funny thing was I couldn't figure out why I was getting signal reports from the other side of the county 50-60 miles away, till I turned up to the rig site and found a fried aerial and saw that I forgot to turn the power down to a sensible 70w/80w. The signal was absolutely booming!

I should have figured when I was getting clear stereo & RDS without an aerial in a Technics receiver over 1 mile away.

It was only designed to cover 10 miles. All good fun, no interference just banging tunes and very happy listeners :D
sharky wrote:
Maximus wrote:A 50w version melted/snapped in half after putting 180w through it.

Image


Woooooooooow :rip

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Re: Hi-Gain Vertical Half Wave Antenna

Post by sinus trouble » Sat Jun 06, 2015 12:32 am

greetings all! :)
ive been working on a low power version of this antenna (1watt) and if im correct?? it seems the whole concept is to basically to transform the 50ohm load to around 5kohm?? the radiator element length remains the same as a standard dipole??
using the parallel LC tuned circuit shown by the NRG ant and shuffys diagram needs quite a large inductor value and a very small capacitance to achieve matching?
as i have loads of variable caps ive focused on the L value so far!
using the 2 x PI x F x L formula? ive needed around 18 turns to be anywhere near 5kohm reactance?
I am as stupid as I look! :|

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Mike Volume » Wed Jul 08, 2015 7:45 pm

sinus trouble wrote:greetings all! :)
it seems the whole concept is to basically to transform the 50ohm load to around 5kohm?? the radiator element length remains the same as a standard dipole??
using the parallel LC tuned circuit shown by the NRG ant and shuffys diagram needs quite a large inductor value and a very small capacitance to achieve matching?
as i have loads of variable caps ive focused on the L value so far!
using the 2 x PI x F x L formula? ive needed around 18 turns to be anywhere near 5kohm reactance?
I understand this is a matter of calculating the parallel impedances as series components (applicable at only one frequency).

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Re: Hi-Gain Vertical Half Wave Antenna

Post by RF-Head » Tue Nov 22, 2016 10:51 pm

For a little project i like to make the 50W version of the vertical half wave antenna
The version as in the picture (melted one)
On the old forum there was a topic with pictures of the 50W version
They used a few windings Blue and brown wire
In the picture of the melted version we only see the blue wire
is there someone that still has the picture of the 50W version ?

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Re: Hi-Gain Vertical Half Wave Antenna

Post by MiXiN » Tue Nov 22, 2016 11:32 pm

RF-Head wrote:For a little project i like to make the 50W version of the vertical half wave antenna
The version as in the picture (melted one)
On the old forum there was a topic with pictures of the 50W version
They used a few windings Blue and brown wire
In the picture of the melted version we only see the blue wire
is there someone that still has the picture of the 50W version ?
Good luck with the project Henk.

I'm sure if you made to order you'd sell a fair few of these as there's a lack of decent verticals for 3M these days.

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Re: Hi-Gain Vertical Half Wave Antenna

Post by shuffy » Wed Nov 23, 2016 12:11 am

RF-Head wrote:For a little project i like to make the 50W version of the vertical half wave antenna
What version is in the pics on page 1 of this thread? Is this the higher power one. A few months back I made a version of this antenna out of complete scrap - leftover bits of perspex and aluminium tube, plus a Philips beehive cap. It worked OK, but I wasn't happy with the tuning. Because the capacitances required are so low, I discovered that the inductance values weren't critical to get in the right ball park and although I could achieve SWR of around 1.3 (and the mandatory RF burns inevitable with this design), I couldn't find a decent sweet spot in the tuning so I didn't believe it would perform as I would have liked. I'm planning on resurrecting this project if I get some time so I'd be interested in how you get on RF Head.

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Re: Hi-Gain Vertical Half Wave Antenna

Post by RF-Head » Wed Nov 23, 2016 8:46 am

Thanks for the reply
I have already made a 250W version last week only need to test it
and realy like to make the 50W version
When it's ready i can make some pictures and put it here on the forum
Also for the coils and capacitor i will make a chematic
Yes if needed i can make one but the biggest problem is getting the antenna in the UK with the big funnel on it
Maybe sending it out without funnel and i give a adress in the UK to buy one

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Re: Hi-Gain Vertical Half Wave Antenna

Post by nrgkits.nz » Wed Nov 23, 2016 9:24 am

There's a guy here in Auckland who makes similar antennas, several people here are using them and they're all encased in PVC pipe, so there's no way water can get in.

I built a NRG half-wave some years ago using parts from an old VHF TV antenna. I used the top of a plastic coke bottle as a funnel to waterproof the impedance matching. For the tuning capacitor I used two rectangular metal plates from the front of an old PC case (where the CD drives are mounted), drilled 4 holes in the corner of each plate and used plastic bolts to hold them together. You need to be careful because as soon as you get any water in matching, the SWR goes very quickly i've found. I managed to get a 1:1 SWR with 30w into about 4m RG58, the meter seemed to show no reflected power.

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Maximus » Wed Nov 23, 2016 10:59 am

RF-Head wrote:For a little project i like to make the 50W version of the vertical half wave antenna
The version as in the picture (melted one)
On the old forum there was a topic with pictures of the 50W version
They used a few windings Blue and brown wire
In the picture of the melted version we only see the blue wire
is there someone that still has the picture of the 50W version ?
Yes I still have the pictures I'll dig them out later.

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Re: Hi-Gain Vertical Half Wave Antenna

Post by RF-Head » Wed Nov 23, 2016 12:44 pm

407099_211702292255576_1878806139_n.jpg
Thanks for the picture
i can see that the brown coil is 4 turns and the blue is for what i can see in the old pictures 3 1/2 turn
if you have more pics yes please
i will make a proto in the next few days
Also fun to read that some of you also used a coke botle instead of a funnel :)
this is also what we have done in the past :)
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Re: Hi-Gain Vertical Half Wave Antenna

Post by shuffy » Wed Nov 23, 2016 2:00 pm

20161123_134223.jpg
Here's a picture of my recent effort, all materials used apart from the beehive, are surplus. It was a lash-up just to prove the concept, and wasn't designed - it evolved as I made it out of the stuff I had to hand. It gives an idea of possible construction techniques though, using perspex for spacers.

For rain cover I've used coke bottles in the past, but my local pound shop has really sturdy plastic funnels. Because of the way the radiating element (top) was offset from the mast, a funnel would also have been offset. If I was to make a proper one, I'd try and get the radiator inline with the mast so a funnel would go on nicely like on the NRG version.
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Re: Hi-Gain Vertical Half Wave Antenna

Post by nrgkits.nz » Fri Nov 25, 2016 8:11 am

RF-Head wrote:Do you have also a picture of the other site?
So we can see how it's made
Want to try to make a copy
This might be what you're looking for
x52yxu.jpg
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Re: Hi-Gain Vertical Half Wave Antenna

Post by RF-Head » Fri Nov 25, 2016 8:24 am

Yes correct that was the one
With the picture of the broken one and this one i can try to make a prototype
If the antenna is ready and tested i will upload some picture etc
Thanks all for your input :tup

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Maximus » Fri Nov 25, 2016 12:03 pm

nrgkits.nz wrote:
RF-Head wrote:Do you have also a picture of the other site?
So we can see how it's made
Want to try to make a copy
This might be what you're looking for
x52yxu.jpg
Nice one, saves me uploading them


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Re: Hi-Gain Vertical Half Wave Antenna

Post by Maximus » Fri Nov 25, 2016 12:05 pm

RF-Head wrote:
407099_211702292255576_1878806139_n.jpg
Thanks for the picture
i can see that the brown coil is 4 turns and the blue is for what i can see in the old pictures 3 1/2 turn
if you have more pics yes please
i will make a proto in the next few days
Also fun to read that some of you also used a coke botle instead of a funnel :)
this is also what we have done in the past :)

Yep the brown coil is 4 turns. It was tuned for exactly 97.00

I'll measure the length of the radiator and post an update


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Re: Hi-Gain Vertical Half Wave Antenna

Post by Frequent Lee » Sun Dec 04, 2016 12:23 pm

I have the original build instructions, plate measurements, coil winding lengths etc for all 3 versions, 50, 250 and 350watt versions. The main failure was the cheap plastic insulation pipe, if you used Teflon pipe instead a 50 version will withstand 150w no probs.

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Re: Hi-Gain Vertical Half Wave Antenna

Post by Albert H » Sun Dec 04, 2016 1:38 pm

Lee - put the details up here for the benefit of everyone!
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