Posts Tagged ‘Antenna’

Cobwebb update

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Posted 16 Dec 2011 — by Alex
Category Antennas

During the summer I finished off my Cobwebb antenna. It was an antenna build that wasn’t exactly testing the idea for me was that it was portable and easy to assemble and take down when I was away on travels for holidays and such like. I used some fairly heavy gauge figure of 8 wire (speaker cable) and found that the resonance was slightly off where I wanted it to be and consequently after a lot of tuning managed a compromise.

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.

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50Mhz Vertical Antenna

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Posted 31 May 2011 — by Alex
Category Radio

With an armful of redundant wire from a previous job (Most of it either 12 or 16AWG) I set about creating a 5/8 50Mhz vertical antenna. The idea was to make a wire version of the G3JVL antenna as featured on the UKSMG website. All the parts came out of the scrap bins at work one lunchtime with the exception of the bolts. Only the hole saw and drill had to be borrowed.

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?

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Cumbrian summer returns

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Posted 25 May 2011 — by Alex
Category Radio

The winds have gone, for now at least the usual 20mph winds have returned.

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!

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Cobwebb build write up

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Posted 01 May 2011 — by Alex
Category Radio

I’ve got round to writing up the build of the Cobwebb so far. There’s a bit more work to be done before I’m completely happy with it but as an antenna it works well for me.

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!

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Spring cleaning

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Posted 11 Apr 2011 — by Alex
Category Radio

Spring brings with it a few thoughts. Warmer days, snow drops, less of a need for thermals just to go in the garden and of course scotch bright. Or if you like scouring pads from Wilkinsons. Its a time for maintenance and tuning up of the old trooper that is the Hustler 6-BTV. Whilst some of it stays out in all weathers other parts stay out even when the salt spray batters the house. Salt in the air = corrosion of my antenna = a healthy rub down with scotch bright (or is it brite?) and a checking of all the connections.

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).

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