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 Cobweb height

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PostSubject: Cobweb height    Cobweb height  Icon_minitimeWed Sep 29, 2021 12:40 pm

I know they say height is might is it worth putting my cobweb up more, its about 28ft at the moment i feel i am missing out some what can probably get to 34ft...
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 6:43 am

Morning Chris
Been looking around on this subject and get all sorts of answers.
Some say 4m high and others say higher but not found one saying "hight is might".
So i don't think going up that 6ft is worth the hassle m8.
I as you know left mine at the 4m as that was where it was tuned and i find it works well for me.
Anybody else want to chip in on this subject or are we the only 2 that use this antenna ????.

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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 7:03 am

It's a folded dipole at the end of the day, so height is important still.  However, my new one is at a lofty 4m waiting for me to finishing tuning it, and at that height, it beats the 80-10 EFHW on some bands for some signals.  Obviously I have a null or two on the EFHW on the higher bands, but that's still impressive!


Last edited by 43CT016 on Thu Sep 30, 2021 8:22 am; edited 1 time in total

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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 7:59 am

Never used one, but worked quite a few people who are using. Heights quoted have been between 3m and 8m. The recent 3m one was a central Europe station, he was doing very well.. not quite a pile up, but I was just one of many he worked one after another, so looks it can work well mounted relatively low.

I'd say if you can get it up a bit higher easily, there's no harm in trying to see if there's any difference.

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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 8:03 am

Lifting it up just 6ft would probably see some improvement but it would be minimal 


I’ve a 3 ele yogi on a retractable mast , and will go from 6m high up to 12m , that’s a 6m difference and will typically see a half to one S point improvement on RX 

Craig

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Alan Pilot
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 8:10 am

So the "Hight is might" is not always true ????.
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 8:30 am

Alan Pilot wrote:
So the "Hight is might" is not always true ????.


Well, the saying really applies to LOS comms like VHF/UHF, and of course higher HF if you're chasing groundwave, hence it being a CB saying too.

For dipoles and the like, it's pattern and radiation angle you care about, and height will affect both.  A dipole at 1/2 wavelength above ground will have a good pattern with no unexpected nulls.  Go higher, and the lobes split and it's less predictable.  Go lower, and more radiates up rather than out.

Of course, with multi-band antennas you then get the usual compromises, because 1/2 wavelength above ground is valid only for one band or frequency!

If I could, I'd have an 80m doublet up at 20m, and a beam for 20/15/10.  Of course, I'd also have the council and neighbours after me, and a costly divorce...so it is what it is. Very Happy

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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 9:55 am

Yes Jeff i should have said in all cases about hight.
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 11:43 am

hi all, just a quick question about di-poles. Would a solid tube di-pole have more gain over a wire di-pole, because the tube has a greater area then the wire, hope this makes sense
regards
mark
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 11:51 am

Markone wrote:
hi all, just a quick question about di-poles. Would a solid tube di-pole have more gain over a wire di-pole, because the tube has a greater area then the wire, hope this makes sense
regards
mark

It would theoretically have wider bandwidth, but gain comes from altering the pattern to push in a given direction at the expense of others.  So change of height to change the pattern, or adding a director or reflector to make the dipole a beam, for example, would do that.

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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeThu Sep 30, 2021 1:41 pm

43CT016 wrote:
Markone wrote:
hi all, just a quick question about di-poles. Would a solid tube di-pole have more gain over a wire di-pole, because the tube has a greater area then the wire, hope this makes sense
regards
mark

It would theoretically have wider bandwidth, but gain comes from altering the pattern to push in a given direction at the expense of others.  So change of height to change the pattern, or adding a director or reflector to make the dipole a beam, for example, would do that.

*exactly this* ..though I've got a way of thinking stuck in my head that more metal up in the air will receive more signals. I don't mean length, which I know will not, but a wider element might theoretically, as well as having wider bandwidth (which I have proven to myself is most definitely the case), intercept a little extra signal, albeit a negligible amount, as a wider element will possibly put itself in the path of the wave that the thinner one may not have been in.

My thinking might be total nonsense like a lot that passes between my ears, but it make me happy knowing I have 'wide' elements at the end of my coax Smile I know it will do nothing to increase TX.
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeSun Oct 03, 2021 8:16 pm

Alan Pilot wrote:
So the "Hight is might" is not always true ????.
He's saying that an extra few feet isn't going to make much difference, not enough to be worthwhile.

It is actually possible to end up being too high depending on where you're trying to contact. The problem with a multiband antenna like the Cobwebb is because of the range of frequencies it covers you can put it up at a height which is great for 20m but will mean you'll not hear anything on 10m below 2000 miles, a problem if you want to talk to Europe.

Here's a plot of gain at various take off angles for antennas at various heights (Courtesy G3TXQ saldy SK)

Cobweb height  Aoa_dipole_elevations

Here's the angle of arrival statistics for South Africa.

Cobweb height  Aoa_s_africa

So on 20m they're all below 15 degrees so we want the most gain below 15 degrees so we put our Cobwebb up on a tower at a wavelength high, 66ft.

However we want to talk to a station in Europe on 10m....here's the same chart as above for Europe...

Cobweb height  Aoa_europe

Now the most contacts are in the angles between 12-15 degrees. but at 66ft high our Cobwebb is two wavelengths high on 10m. Looking at the very top graph at 15 degrees at two wavelengths high theres -15dB negative gain, you'll receive signals on that antenna on 10m at 66ft three S points down from a quarter wave vertical and a whopping 7 S points down from a 10m dipole at 16ft high.

For those on Hamradiodeals.co.uk forums, here's a full link to Steve G3TXQs article:

https://www.hamradiodeals.co.uk/forums/viewtopic.php?f=45&t=16602

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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeMon Oct 04, 2021 8:38 am

Nice one Conor thanks.
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeWed Oct 13, 2021 5:57 pm

Alan,
'height is might' is a term that is most definately true if Dx is what your chasing, if cost is no option and you wish to reduce your noise levels and also to reduce the risk to causing TVI etc to yourself or neighbours.
My 2 element 40m beam and 4 ele yagi are up at 20m, the second tower has a LFA for 10m, a high gain beam for 2m tropo together with a 70cm 25 element I0JXX yagi and 2x35 elements for 23cm.
My best antenna for working around Europe and friends in the UK is a simple dipole at 5m AGL to maximise the NVIS effect to work short distances and to lower the noise level.
Get the antenna as high as you can within limits, choose your operating band carefully depending on what the MUF SFI is doing and try not to break the bank !!
Incidently Anglesey is a beautiful island, spent many happy holidays there as a child and enjoyed flying around the island and the north wales coast when i was a member of the flying club in Dinas Dinlle.

Regards Ady
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeMon Oct 18, 2021 1:57 pm

Mine is at 8metres, clears the ground clutter but doesn't mean I work everything.  Cobweb height  1f62a
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeTue Oct 19, 2021 8:54 am

Have got mine a bit higher now at 30ft extra few ft seems to help, spoke to Mcr who made mine optimum height 27ft to 33ft...
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PostSubject: Re: Cobweb height    Cobweb height  Icon_minitimeTue Oct 19, 2021 9:14 am

26ct954 wrote:
Have got mine a bit higher now at 30ft extra few ft seems to help, spoke to Mcr who made mine optimum height 27ft to 33ft...

At the end of the day, it’s a folded dipole with 20m as the lowest band, so 1/2 wavelength up makes sense.

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