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26ct954
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Call Sign : 26-CT-954
Posts : 217
Times Thanked : 2
Join date : 2020-11-27
QTH or Location : Ellesmere Port
Equipment Used : Na

Cobweb help please  Empty
PostSubject: Cobweb help please    Cobweb help please  Icon_minitimeWed Jun 09, 2021 5:24 am

Just bought a second hand 7 band version,, mcr cobweb having a issue with the  Swr  really high on  20m, its only low at the  moment 10ft till i sort this out, its a twin wire i noticed the wires are twisted can this be my problem,, i am using a external ATu and that get the  numbers low any ideas please... Forget to mention its only a few months old...
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Bean
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PostSubject: Re: Cobweb help please    Cobweb help please  Icon_minitimeWed Jun 09, 2021 10:00 am

Is it to low in frequency ? as in the elements are to long , NC has posted about this before with mcr cobwebb ,all I did with mine was to have more of the wires in contact with each other on each support pole thus shortening the element without any cutting . If its just high all over on 20m then maybe the element has broken or something at the shorting point.
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Northern Crusader
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Call Sign : M0GVZ / 26CT1760
Posts : 371
Times Thanked : 23
Join date : 2019-11-13
QTH or Location : IO94SA
Equipment Used : Icom 7300, TS480, President McKinley, Albrecht AE6110, CRT Mike
Age : 50

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PostSubject: Re: Cobweb help please    Cobweb help please  Icon_minitimeWed Jun 09, 2021 5:19 pm

The wires being twisted don't matter.

I used to own an original made by the original designer Steve Webb. I replaced it by one made by a guy who sold on Ebay under the username MCR666 because Steve Webb stopped making them when he retired.

At the time this guy was the only one making them. When I got it it was instantly obvious it wasn't the right size. Sure enough when I put it up and got the antenna analyser on it the resonant frequency was above the ham bands. Unfortunately because of the lengths of the spreaders there wasn't enough gap between the elements to be able to lengthen them enough to get the SWR down.

I offered to help this guy and went to his house with some parts from my geniune one so he could get measurements and address the problem. He took me to where he made them which was in his bedroom. He had a metal frame bed and was building them and tuning them mounted on one of the poles in the corner of the bed so of course the antenna was capacitively coupling to the metal bed frame barely a foot below it and making it appear electrically longer than it was which is why it was too small. Unfortunately despite his bleating about his knowledge of amateur radio he didn't even think there would be a problem and refused to accept there was. And as far as he was concerned because the rig internal ATU could match it it was fine, even though the original needs no ATU other than for the top end of 10m.

The bloke is an absolute arse who was more interested in bragging about his CD and DVD copying rigs and how many thousands of pounds he was making from pirated vehicle manuals he was selling on Ebay than addressing the issues with the Cobwebs he was selling.

So unless MCR666 has woken up, smelled the coffee and altered his design then none of the ones he sold either directly or through LAM are the right size and there's not enough slack in either the spreaders or the wire elements to be able to extend them enough to correct that.

43CT016 and 26ct954 like this post

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26ct954
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PostSubject: Re: Cobweb help please    Cobweb help please  Icon_minitimeWed Jun 09, 2021 5:48 pm

Thanks for all the info, i didn't pay much for mine £80 which was a bargain will have to keep using the external Atu too keep things safe...
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Bean
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PostSubject: Re: Cobweb help please    Cobweb help please  Icon_minitimeWed Jun 09, 2021 7:50 pm

Mine was the mcr666 5 band version that I got when I first got my licence in 2016 ( and still believe the cobwebb/cobweb is one of the best antennas for the newly licenced to start with for the higher HF ) 10>17m were no problem and worked out the box as it were but the 20m element was to low in frequency and as I said before an extra cable tie on each support arm to shorten the electrical (RF) length sorted that.
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A5H5ATAN1C
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Call Sign : 26-CT-4145
Posts : 85
Times Thanked : 1
Join date : 2021-06-03
QTH or Location : Chatham, Kent
Equipment Used : Includes :- AT-878UV, FT474Gx, AT-5555N, FT-818, DNT M40 (RT Factory, Manpack config), Midland Portapack, IC-211E, TS700G, TS2400, MAXCOM 16E, unbranded 40 channel Japanese 49 & 2.4Ghz transceivers (supposedly Uniden, but unlikely)
Age : 52

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PostSubject: Re: Cobweb help please    Cobweb help please  Icon_minitimeThu Jun 10, 2021 4:12 pm

Can't say much for the type as I've not built one (not the kind I'd buy anyhow), so I'd say you've probably got better insight from the prev responses.

@ Northern Crusader - the leech you described and actively tried to help, sounds like a very familiar type we've all heard about at least in CB and Ham circles sadly.

It's like commercial antennas are marketed with specs based on the reference design characteristics and rarely do the manufacturers or sellers actually air test samples to verify. Amongst the homebrew "sell a few to offset the cost of mine" Chinese copiers or adoptive leeches, it's a mixed bag of the above and maybe flawed testing where they are tested as low-volume builds.

Such arrogance when faced with the exposure of flawed methods, as you've seen, is really way too common especially amongst the leeches who low volume build purely for income because it's always either easily assembled stuff to make parts for, or something 'flavour of the month' in PW/Elektor/*insert preferred title* that's a bit time consuming so a little effort makes for an easy win to exploit the lazy asses out there or just cash in.

I've done rig conversions for TNC specific use incorporating legit Baycom reference modems, shifted about 50 before my source of the LMR FM sets dried up, but I religiously tested every item and didn't ship anything until it was within a gnat's eyelash tolerance of my own first build and certainly didn't do leech opportunistic money grabbing - I only did it because a few people wanted to create similar and I figured that since I had the means, may as well supply some preconfigured. Other than that, my few other customers were people who just wanted those rapidly hard to find sets, that I more or less supplied at cost/cost + shipping.

It's the motivation that differs between the good and the bad, and the good actually learn/incorporate feedback findings - especially when you uncover a schoolboy error in how they designed and built the items.

So, like you, I'm hardly surprised the resonance of the leech build antennas was shockingly off the mark any more than you were when you realised his methods were flawed (to be polite).

But I'm very much one foot cemented in old school engineering and values having grown up around it, just I embrace new ideas better than my wise Oracle sources of inspiration do/did.
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Northern Crusader
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Call Sign : M0GVZ / 26CT1760
Posts : 371
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Join date : 2019-11-13
QTH or Location : IO94SA
Equipment Used : Icom 7300, TS480, President McKinley, Albrecht AE6110, CRT Mike
Age : 50

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PostSubject: Re: Cobweb help please    Cobweb help please  Icon_minitimeFri Jun 11, 2021 2:30 pm

It's a shame he was such a dick about it and didn't address the issues because the build quality was actually quite good and because of how he did the spreaders it actually had fewer points of failure than the original.

I ended up using the wires and junction box with it's supporting arm from my original one on the spreaders and centre plate of MCR666's in the end. The fact it lasted several years and several moves from my house to a farm a few miles away where my radio club does field day when it was used as an antenna for a second station pays testiment to the build quality.
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