Cobwebb antenna advice please.

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bc73
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Cobwebb antenna advice please.

Postby bc73 » 26 Dec 2016, 20:37

Happy Holidays All,

I was just wondered if any of you guys had could recommend a good place to buy a cobwebb antenna, think the original is out of production. I know they are not too difficult to build but sadly i just do not have the time. Any Advice would muchly appreciated.

Cheers Col :thumbup:
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MM6BCF
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andymuza
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Re: Cobwebb antenna advice please.

Postby andymuza » 27 Dec 2016, 03:10

Plenty of original ones end up being sold on various sites so just do a search through sites like this. The originals are great but a lot need work. I got one a couple of months ago and all the fibre glass spreaders where terrible. I cleaned them up and put heat shrink tubing over them to help strengthen the spreaders and make it look good again.

Few variants on eBay
Here you go.

MFJ do a variant available at Navada
MFJ CobWeb
I will not be commanded, I will not be controlled.
n+1 the formula for working out how many radios you need with n being the current amount.

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bc73
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Re: Cobwebb antenna advice please.

Postby bc73 » 28 Dec 2016, 21:21

Cheers Andy, I saw the ones on the bay but hoped someone may have had one of them and could give some info on their quality. I think the MFJ one looks a bit flimsy.
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MM6BCF
108 TM 45

FT-747-GX.
IC-706-MK2G
Stalker 9FDX
Dirland SS3900E
Nato 2000
Amstrad 901
73 and 51

Nothing's ever easy! {bnghd}

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bc73
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Re: Cobwebb antenna advice please.

Postby bc73 » 28 Dec 2016, 21:55

Hi All , Found some reviews online and bought the MCR666 one will let you all know how i get on with it.
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MM6BCF
108 TM 45

FT-747-GX.
IC-706-MK2G
Stalker 9FDX
Dirland SS3900E
Nato 2000
Amstrad 901
73 and 51

Nothing's ever easy! {bnghd}

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andymuza
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Re: Cobwebb antenna advice please.

Postby andymuza » 28 Dec 2016, 22:14

Be interesting to hear your thoughts on it.
I will not be commanded, I will not be controlled.
n+1 the formula for working out how many radios you need with n being the current amount.

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bc73
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Re: Cobwebb antenna advice please.

Postby bc73 » 28 Dec 2016, 23:07

Very much looking forward to building it , do you think i will need an analyser?
_____________________________________
MM6BCF
108 TM 45

FT-747-GX.
IC-706-MK2G
Stalker 9FDX
Dirland SS3900E
Nato 2000
Amstrad 901
73 and 51

Nothing's ever easy! {bnghd}

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kilimax
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Re: Cobwebb antenna advice please.

Postby kilimax » 29 Dec 2016, 11:04

I purchased the MCR 6 band version myself. It's in its box but planning to get it built in the next few weeks weather dependent.
I don't think you will require an analyser to tune it as the design is such that it should be resonant and provide you with a fairly low vswr. You may need an atu at the band edges but the incorporated balun at the feed point should provide a decent enough bandwidth.
Bands such as 10m may require some tweaking depending on where in the band you wish to optimize it for.

I will be interested in hearing how you get on if you get yours on the air before me.
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bc73
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Re: Cobwebb antenna advice please.

Postby bc73 » 29 Dec 2016, 13:11

Had an Email to say its been dispatched , so might get a go at it before i return to work.
_____________________________________
MM6BCF
108 TM 45

FT-747-GX.
IC-706-MK2G
Stalker 9FDX
Dirland SS3900E
Nato 2000
Amstrad 901
73 and 51

Nothing's ever easy! {bnghd}

mark1
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Re: Cobwebb antenna advice please.

Postby mark1 » 29 Dec 2016, 14:45

Ive got the one from mcr666. I took it straight out the box and put it up about 25 foot or so and now its got to come back down to be tuned. 12m is miles out, all the other bands are ok but not perfect so have been using it with my ATU to keep SWR down. My advice to you guys would be to stick it up on a pole about 6 feet or so and get an analyser on it or your gonna be running in and out your shack to keep checking the SWR with a meter as you make alterations. Its a good antenna for the space it takes up and receive is a lot quieter than my doublet.

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kilimax
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Re: Cobwebb antenna advice please.

Postby kilimax » 29 Dec 2016, 15:19

mark1 wrote:Ive got the one from mcr666. I took it straight out the box and put it up about 25 foot or so and now its got to come back down to be tuned. 12m is miles out, all the other bands are ok but not perfect so have been using it with my ATU to keep SWR down. My advice to you guys would be to stick it up on a pole about 6 feet or so and get an analyser on it or your gonna be running in and out your shack to keep checking the SWR with a meter as you make alterations. Its a good antenna for the space it takes up and receive is a lot quieter than my doublet.


That's interesting. Thanks for the tip although I'm surprised to be honest, particularly 12m as the band is narrow enough so it shouldn't really need to be tuned.
Thankfully I do have an analyser so I'll set it up prior to mounting aloft.
I wonder if the dipole lengths are only approximate out of the box? Hopefully your resonance on 12m is low to allow you to trim up in frequency. Mind you, that's the beauty of the design. Elements are easy to replace!

I honestly thought it would be 10m that woukd require tweaking but there you go. Learn somethingnew every day. Talking of 10m, how do you find the bandwidth & resonance?
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mark1
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Re: Cobwebb antenna advice please.

Postby mark1 » 29 Dec 2016, 17:14

Here's how mine is straight out of the box
10m best SWR is at 28.093, 12m is at 24.600, 15m is at 21.170, 17m is at 18.037 and 20m is at 14.240
So as you can see 12m is miles out? i can only assume from this that it was an incorrect measurement of the 12m elements. I can still tune it with my ATU but want to get it down and get it closer to start with.

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bc73
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Re: Cobwebb antenna advice please.

Postby bc73 » 30 Dec 2016, 23:32

Well New Cobwebb arrived today very prompt delivery. will try to get it built in the next few days and keep you all posted.
_____________________________________
MM6BCF
108 TM 45

FT-747-GX.
IC-706-MK2G
Stalker 9FDX
Dirland SS3900E
Nato 2000
Amstrad 901
73 and 51

Nothing's ever easy! {bnghd}

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kilimax
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Re: Cobwebb antenna advice please.

Postby kilimax » 01 Jan 2017, 15:59

bc73 wrote:Well New Cobwebb arrived today very prompt delivery. will try to get it built in the next few days and keep you all posted.


Mine is out of its box and my mast is now down for some winter maintenance which should be completed tomorrow. I'm hoping to get the cobwebb up either late on tomorrow or Tuesday all going well.

I hadn't realised at the time but I've bought the 7 band version! :o
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Tango Mike Callsign 108TM144

I've changed my equipment so many times, I've forgotten what I have

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Re: Cobwebb antenna advice please.

Postby mof000 » 01 Jan 2017, 19:11

YB135 aka M6axl had a how to build in a step by step around 8 years ago...
I can't find it anywhere...
He did have a site called M6axl but that seems to go nowhere now.
I'm sure it's Mr Bix's mate so maybe he can help?
I'll pay whatever i think it's worth...:-)

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Re: Cobwebb antenna advice please.

Postby MH14 » 02 Jan 2017, 12:52

If anyone wants to grab it, I have dumped the original "Cobwebb Revealed" PDF into dropbox. It tells you everything and anything you need to know about the Cobwebb. Some folks assume the CobWebb is just bent dipoles, and miss the fact that the elements are gamma matched.

The PDF gives all the info you need, including the the measurements for the gamma tap points, which saves a lot of hassle when your building your own :)

https://www.dropbox.com/s/90i9xw7ifewfa ... d.pdf?dl=0

Cheers.


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