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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Is there an easy way to tune a G3TXQ cobweb?
At the end of my tether :cry: (excuse the pun)

Tried folding back and using cable ties but they're either too tight or too loose when tensioned. Tried terminal blocks and cable ties. Cutting/folding/cutting..

Anyone got a fool proof no mess way of doing this please?

Is there a magic gap and fold back formula?

Cheers

Dave
M6XMA

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Sat Sep 12, 2015 5:58 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
I've never tuned a cobweb but would using a piece of elasticated shock cord to finding resonant length not make it handier....then later after the lengths and spacings are established change the shockcord to something else.

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Sat Sep 12, 2015 6:23 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
ei9ju wrote:
I've never tuned a cobweb but would using a piece of elasticated shock cord to finding resonant length not make it handier....then later after the lengths and spacings are established change the shockcord to something else.


Thanks for the suggestion :thumbsup: It might if I had some.

My problem seems to be the loops slipping when changing the spacing and it seems you need to have a cable tie next to the loop and one at the end of the loose wire or else the resistance changes. (suppose I could use insulation tape for the loose end)

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Dave
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Sat Sep 12, 2015 6:41 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
The original G3TPW cobwebb merely uses cable ties on the fold backs and heatshrinked string to link between the looped back ends of the elements.

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Sat Sep 12, 2015 8:58 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
when I built mine I folded the wire back on itself and wrapped the dangling bit around the wire and used shoe laces to pill ends together
took a swr plot on the analyser calculated the resonance into a length then calculated the resonance length at the freq of interest
subtracted one from the other and shortened or lengthened accordingly took about 30 minute to tune when tuned I just tie wrapped the foldback in place still wrapped around the wire, shoved it up tyhe mast and works a treat..
Should add singlw wire dipoles as TXQs details

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Sat Sep 12, 2015 9:10 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
Beg, steal or borrow an analyser with a graph readout and you'll have it tuned in no time as it removes the guesswork, it lets you see where the antenna is resonant, be that above or below the desired frequency, so you know whether to lengthen or reduce the element, not only that but it'll also display all 5 resonant dips at once letting you see what, if any, the effect of adjusting one band has on another.

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Sat Sep 12, 2015 9:39 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
I'm not clear what the question is, is it the tuning, or the tying?

When you are tuning it makes little difference whether the tires are dead tight or a little loose, so when I tuned mine, I didn't put cable ties, just folded them back and twisted them tightly, and put elastic bands between the loops in the wire

When it was tuned, I put cable ties, and through the loops in the wire, cord, which was then easy to tension. It's been up a while now, and shows no signs of drooping, though I have some shock cord to install in addition to the cord should it start to look scruffy. I also put cable ties on the cord just to ensure the knots don't slip.

As for the tuning, I tuned each band roughly right, then went back and fine tuned each band. That way the fine adjustments will not detune other bands. If you try and tune one band exactly when the other are far out, adjusting them will affect the first one.

With a graphical analyser, it is very quick, especially if it has good enough screen resolution to show the proper position of the dip on all bands at once.
With a TX and SWR meter, or an MFJ type analyser, it will take longer, but the process would be the same; get them all near first, then fine tune.

I tuned mine about 8' from the ground, and it made little difference putting it at 20', though it does rise in frequency as it goes higher (or clearer of the ground and other things)

The fine tuning can mean moving the fold 1/8", it is quite sensitive. Mark the fold with a marking pen when you are close, then you won't be left wondering how much you moved it.

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Sun Sep 13, 2015 3:19 am
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
Thanks very much for all your helpful suggestions and experience.

I should have said that I'm using a 259b and a sark clone with Bluetooth to a tablet so think I'll just use the 259b for the final check.

I'll report back later :)

Cheers

Dave
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Sun Sep 13, 2015 11:09 am
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
Thanks again chaps for taking the time. It is appreciated :)

I went with a loose cable tie over the fold back near the loop, tape over the dangly end and a shoe lace to tension (top tip :thumbsup: ). Then following Sangoma's tips success at last!

Tidied it all up once tuned with cable ties. 20, 17 & 15 SWR 1.0 with 12 & 10 needing a bit of tweaking still.. Up at 10ft and working beautifully.





Cheers

Dave
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Attachments:
cobweb.jpg
cobweb.jpg [ 119.31 KiB | Viewed 1337 times ]
ties.jpg
ties.jpg [ 98.77 KiB | Viewed 1337 times ]

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Sun Sep 13, 2015 6:14 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
Excellent news Dave. The resonant point will go up a bit as you raise it in the air so better tuning slightly low of the centre of what you want if you're planning on raising it in the future.

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Sun Sep 13, 2015 7:04 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
I'm a bit late to the discussion, but this is what I use on my cobweb and hexbeam:

Image

A piece sliced off a "choc block"; insulating cord with a knot in it (to stop it falling off) on one side; antenna wire in from the other end.

Steve G3TXQ


Sun Sep 13, 2015 9:07 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
G3TXQ wrote:
I'm a bit late to the discussion, but this is what I use on my cobweb and hexbeam:

A piece sliced off a "choc block"; insulating cord with a knot in it (to stop it falling off) on one side; antenna wire in from the other end.

Steve G3TXQ


Thanks Steve :)

I wasn't brave enough to cut to the exact length though I did use your guide and added a few extra inches to each piece.

Cheers

Dave
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Mon Sep 14, 2015 9:00 am
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
Dave,

That photo is a bit misleading. I push the antenna wire quite a long way through the choc block to start with, and then trim it back during tuning.

Steve G3TXQ


Mon Sep 14, 2015 4:20 pm
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
G3TXQ wrote:
Dave,

That photo is a bit misleading. I push the antenna wire quite a long way through the choc block to start with, and then trim it back during tuning.

Steve G3TXQ


Thanks Steve

That makes sense. I've got another 2 to build so will try this approach on at least one of these. Can I just ask what size blocks you used? I think the ones I have are only 3 amp so quite small bore.

Cheers

Dave
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Tue Sep 15, 2015 10:32 am
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 Is there an easy way to tune a G3TXQ cobweb? 
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Post Re: Is there an easy way to tune a G3TXQ cobweb?
I can't quote you an amperage - I long since lost any packaging. But I can tell you a 4mm bolt fits inside easily, and a 5mm doesn't!

Steve G3TXQ


Tue Sep 15, 2015 3:00 pm
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