Tag Archives: home-brew

Compact half-square for 40m band

I’ve just had an interesting discussion on 40m this evening with Peter, OH6GHI, also an antenna enthusiast. I happened to mention that I was listening to him on both VFOs. VFO A on my dipole and VFO B on my vertical and I found the stereo image very interesting as the polarisation of his signal to me changed.

half-square-basic-designWe got talking about half-squares and I confirmed that we were talking about the same thing, basically 2 x 10m verticals separated by a 20m top section. The half square is fed in one corner and according to my MMANA model, this should present 50 ohms and a great SWR curve across the whole of 40m.

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How to use dual coax feeders as ladder line

palstar-at4kHaving recently taken delivery of a Palstar AT4K manual tuner, I was keen to get her into production to replace my CG5000 in the attic.

Problem: the route to the attic from the shack is complex but I have a number of spare coax runs going that way including a couple of RG58 cables that I installed about 10 years ago as backups. Actually I originally installed three RG58 lines but I’ve been using one of them to send 12V up the line to the ATU.

parallel-cox-to-ladder-lineAfter MUCH research, I finally used about 20 feet of parallel coax feeders, connecting ladder line to both ends. To clarify, I run about 12 feet of ladder line from the ATU to the parallel RG58 cables. I soldered the ladder line to the inner core of the RG58 coax and shorted the braid-to-braid. My 20 feet of RG58 runs to the attic, through walls, up ceilings etc and in reverse, I connected the ladder line to the RG58. Again, I shorted the braids of each line to each other with a solder blob. My ladder line then has another run to the feedpoint of a large 60m loop that runs through the attic and around the garden.

The results have been quite amazing. Comparing my 40m reference dipole to the the CG5000 (SG230 type) ATU feeding the 60m loop has always shown that the loop was about an S point lower than my reference dipole for most stations.

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How to build a tilt-over 60 foot antenna mast from scaffolding poles

This job is not for the feint-hearted. You will need a natural tendency for engineering, be accurate and be comfortable with knots. However, there’s no reason that most small teams of keen amateur radio operators can’t build this as a project for field day use.

Let me explain how I built the one shown in the pictures, then I’ll cover the learnings with you later along with my own do’s and don’ts.   Continue reading

Budget Tilt-Over mast from Barenco

(This article contains an animation)

barenco-special-screenshot(Note, this product is at the “enquiry” level, it is not a stock part from Barenco)

If you haven’t heard of them, then you should. Barenco make the finest brackets and supply other amazing stuff for the amateur radio hobby. Here’s Brian’s link:

http://www.barenco.co.uk/

I dropped an email last month to Brian asking him for some custom work but explaining something in writing that will produce a piece of engineering can cause spurious results. I therefore used my new (free) toy, a 3D modelling program called SketchUp to show Brian what I was after.

Essentially, it’s an off-set, side-mount rotator bracket that is also tilt-over. Since the bottom of this mast will only be about 2.5 above the ground, I’ll easily be able to secure the rotator bearing, undo the bolts at the top and carefully lower the mast down with a 6:1 pulley set I have.

Here’s the walk-through as an animation:

My pole connector

Aluminium Pole Clamp

You’ll see in a number of pictures, the use of a large slab of aluminium that I had to make up to allow the bottom section of my 12 meter mast to clamp to a pole. A pair of standard of 2 inch double clamps wouldn’t fit Moonraker’s fibreglass mast. The bottom diameter is 58mm (about 2 1/4 inches). I found this slab on eBay and won it for a tenner. It’s heavy though – don’t think it’s a light just because it’s aluminium. Of course, in steel it would be loads heavier.

It is such a handy piece of hardware that I sometimes wonder what I’d do without it, particularly as I was bright enough at the time to drill a few extra holes in case I needed them (which I do for the 40m dipole!)

I’ve also discovered that the top 8 meters of my fishing pole fits perfectly on the 12 meter mast with a piece of plumbers tube as an “insert”. The 12 meter mast fits on the 6 meter aluminium pole too. That’s a 5/8th for 40 meters or a full sized quarter-wave for 80m!

Pringle Tin Waveguide Antenna 2.4 Ghz project

Not being able to resist the pull of the decibals, I raided the larder tonight for a Pringle tin to build a wave-guide antenna from scrap parts. This is the story of that project.

Manufacture: I soldered a 30.5mm (quarter wave) element to a UHF bulk-head connector and drilled out a hole in the Pringle for hot-glueing. Exactly how far away from the base of the tin I should fit the element took ages – and lots of conflicting web pages. In the end, I aimed for 1/4 wave from the back of the tin. Someone is going to tell me that this is probably the most awful place to stick it – I can believe you :)

Pringle Tin Waveguide Antenna 2.4 Ghz

My multimeter couldn’t get a reading on the foil inside the can so I used kid’s water based glue to stick sheets of tin-foil to the outside. This tinfoil was grounded to the base of the tin, although I had some difficuty in doing this because there appears to be some sort of laquor applied to the base. The copper wires seen in the photo were to act as a physical and an electrical assistant; to provide a good ground to the outside of the can.

Ater connecting the Pringle-Wave-Guide to a buffalo wireless access point, I turned it in the general area of the kids room that was running NetStumbler on their network card. I waggled the can around in my shack, and went to the kids room to check if the signal strength had risen at all during the waggling. No luck. So far, it’s as much use as a dummy load.

It just goes to show that some experiments just fail.