Posts Tagged ‘Cobwebb’

Portable Hexbeam v’s Cobwebb

After a few more weeks of not getting on the air I managed to man handle the portable Hexbeam up to about 4 above ground level (Note: must get that tilt base sorted out) to compare it against the Cobwebb I have in the loft.

So before we go down the ‘It’s not scientific’ route. I’m ok with that, no big deal its just a bit of fun.

There are some significant differences between the two antennas that I hadn’t fully appreciated. Firstly the noise levels on the Cobwebb were quite a bit higher, which seemed to make the Hexbeam sound quiet, when in actual fact there was no significant difference on the higher bands when it comes to S points. But, the lower noise levels made it much nicer to use. The image below shows what I mean. There is a band of ‘mush’ slap bang in the middle where I switched onto the Cobwebb. Just so you know, the Cobwebb was way quieter than the vertical I had before.

cuSDR Hexbeam vs Cobwebb

It’s not a huge visual difference on the screen but the ears make it obvious. The gain on the Hexbeam made it easy to make contacts with C06LA answering on the first call, I’d never expect that on the Cobwebb.

You can also see that the signal strength is fairly similar, that was W4UH calling CQ.

So not much in it when the Hexbeam is really low, I’m sure it’ll beat the pants off the Cobwebb at 12m but interesting to see that the Cobwebb is ‘noisier’. Especially as I thought it was quite a quiet antenna.

Cobwebb success

After what seems like a lifetime in the attic the Cobwebb ventured outside for the Easter weekend. What a weekend as well.

I put the little antenna up on the telescopic pole about the same height and the top of the Hustler 6-btv (in the background) and spent a few minutes tuning into various stations then dashing in and out of the house to swap the feeder over between the two antennas. Several dashes later and the freezing cold east wind finally kept me in doors just as 2 VK stations appeared on the cluster. At the time I was on the vertical and paid little attention to them as experience tells me that they wouldn’t be ‘in range’ with my 100w. Especially as I was at home in the st bees dip which usually strips rf out of the ether. I tuned to their operating frequency and was met with stoney silence, as expected.

Out of curiosity I did one last switch and the first station was a real 5 & 9. A few calls later and we managed my first qso with a vk. A few minutes later I bagged my second. Within a few hours I managed 7 new countries in between walking the dog and other family stuff. I can safely say that I will be making a more rugged version of the single wire Cobwebb and retiring the vertical.

Now the bands have returned to their usual quieter state it was certainly a good weekend to be on the radio

image

 

Cobwebb at a price

Lamco have added a new product to their range. A Cobwebb antenna. It goes under the name of a MyHam HF-7B and it is specified as an antenna with a useful range of 20/17/15/12/10/6/4m bands.

I noticed this in the latest Practical Wireless and thought I’d email a copy to Mike Corke, ZS1RJQ who has now made 6 of these. We are both users of the Cobwebb but both of us have homebrewed versions. I was interested to see how much his cost to make and like me, he spent about £40 making each of his. Mine  was a little dearer on account of me making a few experiments along the way. We both had a little chuckle at the cost of this commercial version at £249.

If you need an HF antenna then it seems that the commercial versions are very expensive and homebrew antennas cost a bit in time but a lot less in terms of £. I buy my bits and pieces from all sorts of places but AMTools / Spratreader on eBay has all the bits you need for the hardware for a much lower price. If you don’t see what you need then just email him and I’m sure he’ll be able to help.

If homebrew isn’t your thing then there isn’t much of an option. But it seems it’ll cost you for a simple piece of hardware. I’m sure if I were to every build my own rig it’ll look like a dogs breakfast and perform in a similar fashion but simple bits of wire shouldn’t cost that much.

(Just to clarify I’m not singling out any one supplier, but just observing that off the shelf stuff can cost a fortune compared to home made stuff.)

Single wire Cobwebb antenna

Last summer I built myself a Cobwebb antenna and was fairly pleased with the results. I did think it was a bit heavy and was looking to repeat the build with some lighter weight wire until I came across this article from a well-known antenna buff, G3TXQ. It looked like just the ticket so I copied the design and low and behold after a few evening work I finished it off. Here it is during the tuning phase of work which I completed over the weekend (which by the way is as simple as tuning any dipole).

By the way the tropical weather (read blue sky) in St Bees is a welcome change from the recent flooding. I doubt it’ll last though!

You can see the usual antenna laying down in the background, which is a Hustler 6-BTV vertical which has suffered at the hands of the strong winds and salt air we get here. Once I had assembled both the antenna’s I was able to make a bit of a comparison between the two. The vertical is a good S point down on the Cobwebb on 20m, 17m and 15m and about the same on 12m and 10m (at that height!). To be fair it doesn’t have the 17m stub so that’s a bit of a poor comparison. I did managed to get it a little higher with the fishing pole but need to work on the mounting point and ‘environmental protection’ that it’ll need to be used here. Either that or it’ll go into the loft with the 40m dipole that’s up there at the moment.

For some reason I really enjoy these antennas, either to build or use but Michael, ZS1RJQ who I’m in regular contact with over email has built a fair few more than me. His are far more robust than mine but between us we’ve discussed the hardware side plenty of times and before long we’ll end up with an optimised lightweight design. This one is so far the most compact and well worth a tinker if you’re into that. Thanks to G3TXQ for the original design.

With Halloween coming up shortly maybe I’ll put a spider on it!


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