Cobweb antennas

[VK4WDM]

My main HF antenna is a Butternut HF9V multi-band vertical which works very well, but it is always handy to have a "horizontal alternative" which sometime works better, especially on the higher frequency bands. Up until recently this role has been filled by a 40m horizontal loop but the relocation of my shack and the growth of a tree means that I can no longer use it and an alternative has to be found.

A hexbeam has been suggested but I do not have a rotator, so the other alternative would be a cobweb. Interests me because:

Low cost - I have all makings already.
Small foot print that suits my sized yard.
5 band with no need for a rotator.
Made mostly of wire which suits a TAWAN.

There seems to be two types, the original that uses folded dipoles made from speaker cable: http://test.g0mtd.co.uk/CB1.pdf and another variation which uses single wires and a balun: http://www.karinya.net/g3txq/cobweb/

Cobweb antennas seem to be very popular in the UK and I would be interested in hearing of any VKs use them and how well they work (yes I know they are a compromise - that is what I, and many others, have to live with).

73

Wayne VK4WDM

[VK3MEG]

the moxon not cutting it wayne?

reading about it I can see where you are going. do you run an amp?

hmmm they are a compromise why not go for a hex beam and use arm strong to turn it. they seeem to have more gain and are a better alternative. The people I hear running them (cobwebs) get excited about little stuff that you or I would dismiss.
The hexbeam has many things going for them they hear ok and tend to provide better outcome than the cobweb if you can have a chat to vk4kus steve he has great success with them they can be turned with a small tv type rotator all though not the best option.
The hex is the option I would pursure well b4 the cobweb. I shudder when I think what i would do with out my yagi.
good luck.

[VK4WDM]

Hi Steve

The Moxon is only for 10m. No amp here and I can't really afford to buy or run one, but I can usually work anything I hear just with the 100w and a bit of patience. A Hex beam with an Armstrong rotator is a possibility, but the amount of room I have is quite small - that is why I had to sell my triband yagi, but it did not work well with my 8m height limit anyway.

73

Wayne VK4WDM

[VK4WDM]

I guess the best way to proceed is to do the experiment. I will build a quick and dirty Cobweb using some PVC pipe and the centre hub from my ill-fated vertical delta loop. Maybe just a couple of bands to see how it goes.

73

Wayne VK4WDM

[VK3BY]

Wayne

Try an email to Denis VK3BGS, he has a cobweb antenna up and has been using for a number of years.

Cheers

David
VK3BY

[VK5TM]

If you do email Denis (and with Denis's permission), could you put the replies here as I would be interested as well.

Thanks
Terry

[VK6ZFG]

Wayne

Check out "B" hardware. They have green plastic garden stakes, solid 16mm dia, up to 2.4M long and do not cost too much. They might be long enough for what you need and would be much stronger than PVC pipes you are considering using.

I have been looking at them as possible spacers for a quad turnstile (if I get around to building one).

[VK5TX]

The green stakes have a iron core

[VK6ZFG]

I'm now confused.

I just cut one of the thinner green ones (10mm) and that was plastic all the way.

However a mag base shows it is magnetic. Cutting it further along away from the end hits metal.

There are black square stakes. Maybe these are non metallic?

[VK4WDM]

The green stakes have a iron core

OK, so the question is what is going to happen if I make a Cobweb with them? Intuition says it won't work but I am enough to do the experiment. If it does not work I have four tomato stakes and I go back to PVC pipe

73

Wayne VK4WDM

[VK6ZFG]

Basically they will be a conductor slightly shorter than the length of the stake. They will act like a guy wire broken periodically with insulators. As long as the lengths are not frequency related and relatively short frequency wise they should not have a too detrimental effect.

[VK2MUS]

If you can find them or know some one - the spreaders used on high tension lines are ideal for a cobweb
john

[VK4WDM]

I got a long ladder and a hacksaw and I know exactly where the HT lines are around here - in the direction of the loudest buzz

Wayne VK4WDM

[VK3BGS]

For those interested here are my comments on the G3TPW version of the Cobwebb Antenna.
I have been using mine since May 2013 and have had good results with it. Yes its not a beam but you have the advantage of it being horizontal for less noise pickup than a vertical and its omni directional so there is no need for a rotator. I have the G3TPW version from Steve Webb and the construction is solid and well built. The spreader arms are made of a combination of fibreglass tubes and rods which form a tight and solid fit and has little movement in strong winds. As for the wire it is not speaker wire but appears to be electrical grade wire and has shown no sign of stretching so far. My back yard area is only 3.5 x 7.3 meters so not a lot of room to play with. I have mine mounted on a Nally 7.7 pipe mast with a Diamond X50N above that and all appears to work fine with little or no interreaction. Plus I can still lower and tilt the Nally when needed. Now to performance and it does work very well on 20 and 17 meters but on the higher bands while ok I wont call it great but under ideal conditions it is possible to have some qso's. I have worked qrp stations in the UK so the antenna is certainly not deaf on 20 at least.Would I like a beam, of course but its not possible in this location but the dream remains to this day. I am considering an amplifier but the cost is a challenge at this time as a retiree. I have heard and worked a lot of stations using Hex Beams and Spider Beams, but from my observations the Hex for size and gain has it. But sadly its too large for my current location. There are several plans around on the net for making your own Cobwebb which I suggest would be cheaper than a purchased one. I don't have that facility so had to buy, but I am totally satisifed with what it does and it is definitely better than using a vertical. One station that I know is using an original, like myself is Jason ZL3JAS who actually took it to New Zealand when he emigrated there some years back and is heard very loudly in the pacific area and he manages to work a lot of stations. He was one of the reasons I eventually settled on the Cobwebb myself. Jason does use a bit of power also usually about 700 to 800 watts.

Denis
VK3BGS

[VK5TM]

Thankyou for the information Denis. Most enlightening.

Having a bigger back yard, I think I will look into a hexbeam if I can get all the bits at the right price.

[VK4WDM]

Have a word with Barry VK4TI. He built a Hex beam from locally sourced materials a few months back.

73

Wayne VK4WDM

[VK3BGS]

Hi Terry
Value for money against performance the Hex Beam is hard to beat.
I have heard and worked so many of these on air I am more than impressed.
Plus you don't need a huge rotator which cuts down the cost.
I know what I would have if only I had the space.
But things being as they are I am more than happy with the Cobwebb.

Denis
VK3BGS

[VK5TM]

Thanks Wayne, will drop him an email over the weekend.

Denis, the wonders of money and what-if, a time machine would really come in handy about now, wouldn't it.

Happy New Year all.

[VK4WDM]

John VK3MUS suggested that the spreaders used on HT power lines would good for a cobweb.

Does anybody know who supplies them to the power companies? I am a bit reluctant to approach the local power supplier. I had a major run in with them last year over a noisy pole and they probably have block on my phone number and a little effigy of me hanging on the wall with pins in it.

73

Wayne VK4WDM

[VK1DJA]

Wayne

What length of rod do you need?

There are fibreglass electric fence posts that are about 10 mm diameter, but seem to be 1.5 M max length. Pretty cheap from your local rural supplies outlet.

Dave