I did notice that I had made a small dimensional error that had gone un-noticed and caused me quite a bit of bother when trying to tune the antenna.

Modelling the Cobwebb antenna is a little more complicated than you may imagine. The construction is based around twin cables and basically the effect of having 2 wires close together gives MMANA-GAL a bit of a headache.

I had to laugh as even I can get the SWR a little lower than that!

Seriously though the modelling package is similar to the EZNEC flavour which I have had a play with in the past and its something I would like to get my hands a bit more dirty with in the future. My Sotabeams MFD is looking a little tatty after some heavy use last year and I’d quite like to make up a rucksack antenna that fits my pack and that doesn’t get blown over in the strong winds we get here on the fell tops in Cumbria.

What is good about all these mistakes and mishaps is that they are free in terms of money, they only cost a bit of time and without this learning I doubt I would still be that interested in ham radio. There are of course frustrations but these are far outweighed by the successes. I can’t thank the dedicated and talented individuals enough who put out the various pieces of software that allow us to tinker effectively for nothing.

Its figures suggest its a good yagi for my QTH for use with the local net and SOTA / WOTA on FM and into the NI repeater GB3NI at a push.It’ll also be useful for any back packer work as well as club special event stations if needed. The website throws the usual information and as always it should be read in conjunction with your own experience of your site. Never less the numbers are:

Gain: 11.16dBi @ 145MHz

F/B: 19.59dB @ 145MHz

Peak Gain: 11.18dBi

Gain 10m above ground: 16.93dBi

Peak F/B: 20.32dB

Power Rating: 5kw

SWR: Below 1.4.1 from 144MHz to 146MHz

Boom Length: 1.789m

The antenna came in a large cardboard tube but with nothing else in it, no clues as to assembly, which is odd as you get pages of helpful advice from people like Sotabeams who sell cheap out and about antennas. It also states that the elements are solid 1/4 inch (6.35mm). Although mine were not and the use of high quality insulating blocks is let down by the choice of threaded inserts. Which in my case spun one the box section holes that were drilled and made the insulators sit slightly proud of the section and hence area point which over time will allow fretting. One of the elements isn’t quite as secure as it could be and when I looked inside the box to see the type of insert used I was met by quite a few bits of swarf. Nice!

Still, the new toy is up in the loft (until I can sort out the wobbling elements. Each block needs a deeper countersink in order to make sure the raised insert sits fully inside the insulator and not on the taper of the countersink, if you follow that. The spinning insert will be dealt with by a bit of Loctite 603 or other bearing retainer before the holes get too big.

Whilst I am cheesed off that the manufacturing quality is a bit below par for my liking I’m sure once I’ve fixed the issues it will be a very useful antenna. Here is is in the loft aiming at GB3NI and getting in (just) and you can just about see a bit of the non perpedicularity / wonkiness of the loose elements. Once the go ahead for an exterior installation has been approved by  the in house planning department I’ll be fixing it outside to make the most of the beam. Until that occurs I’ll be manually rotating it by going up into the loft and moving it about, There’s plenty of room up there so there is no problem and means that it’ll give me the kick I need to board out the rest of the central part of the loft.

Two things have caused a bit of heartache with this antenna (I think heartache may be a bit strong but they were annoying enough to make me want to look at it again) were; firstly, the weight of the thing hardly made me want to hump it up a fell and when out and about on SOTA and WOTA activations I reached for the lighter weight (but poorer performing) miracle whip whenever I was planning on an HF activation. The other bee in my bonnet was that it was a bit of a hassle to assemble as there was wire everywhere that didn’t form a nice shape round the antenna. Not a performance issue but it took a while to ‘organise’ it.

I came across an article on G3TXQ’s website which moved the chokes to the centre feed point and did away with the need for figure of 8 cable and a tapping point. So I’ve ordered a couple of ft140-61 toroid’s from AMTools on eBay and time permitting will be putting together a single wire Cobwebb to make a comparison over the Christmas holidays.

The instructions are fairly self explanatory and it shouldn’t be hard to follow, or so I thought. As with most of the designs on the internet I found that there wasn’t much to back up the picture should anything not give the results you were looking for. Would you believe it but mine just doesn’t want to be resonant at 50Mhz, 40 yes or maybe 41Mhz but 50Mhz? Not today, or tomorrow for that matter. So its to the scrap bin again to find out the problem. I suspect its down to the coil.

I knocked together a wound coil which I can tap at any of the whole coils, wound round a piece of ~20mm OD PVC pipe. I will use this to see if I can get the beasty to be resonant on 50Mhz or thereabouts by changing the tapping point. If it all went to plan then it wouldn’t be any fun right?

Time to put he antenna back up. I do like my vertical antenna. the hustler 6-BTV is a good compromise for me with a low visual impact and adequate performance. Living in a valley is never going to be ideal for exiting RF but the 6-BTV does a good job. It does have a fatal flaw in its current un-guyed location. The wind. Living on the west coast, especially bordering the lake district national park means two things weather wise. Wind and rain. rain is ok but every now and again when the swr drifts too much then I have to take the thing down and let it dry out. the other is wind. the aluminium tube and heavy top coil whip the thing about when the wind gets up and one day it’ll fail from fatigue.

Now I know where that fatigue is likely to be. The recent winds have given the vertical a slight bend, undetectable when you’re up close but from a distance and with a reference point its like the leaning vertivcal of St Bees. It’s very unlikely to have affected the performance and reinforces my need for indoor antennas (in-tennas) like my newly constructed Cobwebb.

If you need some inspiration I can really recommend the stealth antenna book by Steve Nichols. Its abosultely full to bursting point of HF antennas of every shape and size, there’s bound to one that fits your space. Its quite light on vhf ones but has pointed me in the direction of the cubic quad that is vying for a place on my homebrew list. Soemthing for 2m or 2m & 6m would be nice. I can almost feel the XYL getting cross with me again!

I’d recommend this as a project as it was quite easy to do and the results for me were very promising and I certainly don’t think I’ll be looking to use long wires on my trips about now. this is much more compact (once extended) and didn’t get the mother in law too upset!

I don’t have particularly big fingers and now they are a little smaller round the knuckle area having had to rub down the inside and outside of the tubes. A small price to pay now that its back and resonant in the right place on the bands. Checked thanks to the loan of the clubs antenna analyser. I even had a chance to permanently fix the Watson 80 plus 2 in the loft and make good all the connections etc for when its just too nasty outside for the vertical. A quick check in the contest arena that is every HF band every now and then and there isn’t much in it with both the antennas. US east coast stations were a bit noisy but still managed to work half a dozen on the various bands.

All this clearing out of corrosion and making the station work again got me thinking about the 6m beam that’s in the loft. I had moved it there last year and found it wasn’t too good and actually performed better outside on a 3m pole. The XYL doesn’t want it fixed to the house and a mast is out of the question. No idea what to do with it right now, I think I’ll dismantle it and wrestle it downstairs after I’ve finished the decorating (got to keep in the good books).

Then there’s the other question to balun or not to balun at the antenna end or just at rig end. Clearly my mind isn’t made up so anyone with some good advice please let me have it before I get carted off for not knowing my ahem from my elbow. Us mechanicala engineers loose confidence with all the electrickery sometimes!

Living on the west coast brings with it a few challenges. High winds and salty air arre the two which normally spell the death of anything remotely metallic. However I’ve found another little gem courtesy of my Hustler 6-BTV.

Owning a vertical is a big compromise. Performance is sacrificed for low visual impact and its a compromise I’m prepared to make. What I’m not too keen on is ‘less than optimal’ engineering. By which I mean jubilee clips. There are a few of these on the Hustler and they are simply not man enough for the job to coin a clanky term. Whenerver the antenna moves then the opportunity for the finely tuned stick to detune itself by alterting the length. This time I’ve found some 1 1/8″ PVC pipe and cut off a load of lengths in wonky er I mean imperial untis to match the manufacturers recommended start point. When the weather is a bit more conducive and I can pinch the clubs analyser I’ll have another go at tuning it so its resonant on the right frequencies.