Building a 10m Coaxial Vertical for home

Given some of the activity that I’m seeing on 10m, last night I went to build a quick and dirty 10m vertical dipole but found I was lacking a couple of the bits that I wanted, so given that I was going to ave to buy some things anyway, I decided to make something a little better.

A little web searching showed up this article. The only thing that I was unclear on is where the author got his percentage of wavelength sizes for the driven element and the coax from. I am assuming it’s an adjust meant for velocity factor but he used Aircell 5 which has a velocity factor of 88, in which case the length of the coaxial element is substantially short as it looks to assume a velocity factor of 60%. I can’t find any coax with that velocity factor.

I’m assuming that it is velocity factor. I will be using RG-58CU the vf is 66, and I will assume 98 for the aluminium pipe that I’ll use for the driven section, the measurements that I will run with for a vertical centred at 28.300 MHz will be

Coax element – 1.749m
Driven element – 2.597m

The basic Idea that I have is this:

10m Coaxial Vertical

I’ll actually cut the tubing a little shorter as I also bought a short length of 10mm tubing that I can put inside it, for fine tuning. I’ll use a hose clamp on it once I have the length correct.

For the choke, I’ll do about 12 turns of RG174 around a pair of ferrite toroids. This will be mounted in a small box. The antenna coax will connect to the choke via BNC connectors and the antenna via an SO239.

Well, there is the theory. I guess I need to start looking at some practice now.

Step 1 – The Choke

Similarly to the linked article, I decided to use a pair of 35mm Ferrite toroids, but as I couldn’t quickly lay my hands on some RG400, I made it with 12 turns of RG174U.
DSC_0133

I was sure that I picked up some round lugs today so I could do the earth of the SO-239. I must have dropped them before I got to the counter. What I ended up with is a little less tidy, but it works. I also put a 25mm M6 Nylon bolt through the case to old the toroid in place.

DSC_0134

Checked it for shorts, then for completeness had a look at the inductance of the braid. 215.1 µH.

DSC_0135

and there we have the completed choke.

Next step into get the BNC on to the coax end.

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With a bit of heat shrink for tidiness and good measure.

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and it attaches properly to the choke. The next part will be measuring and cutting the coax.

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That’s the coax cut to 180cm with the braid cut at 175cm, which hopefully should be the values I need.

Now comes some work with the hardware.

I can’t find my tape measure to work out how much to cut off the 3m tube, but I recalled that the bit of wood I bought was just over 2.2m. Given that I have a 1m adjustable section that I can slot in, I decided to cut the 12mm tube to that length.

Next step is the U-bolts into the bit of decking that I am using for the bottom.

DSC_0139

I’ve placed the U-bolts about 25cm apart and I’m using the 80cm section of the 12mm tube to make sure that I’ve got sufficient washers to bolt it up relatively tightly.

DSC_0140That’s starting to look pretty good.

Now, given that I forgot the round lugs, I need to reconsider how I attach the centre conductor of the coax to the tube.

It occurs to me that I bought two hose clamps. I could clamp a spade connector to the tube with that.

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Like this.

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It’s coming together and I’m starting to get a little excited about being able to test it tonight.

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OK, it’s not properly visible here but there is a minor problem. That 5cm of centre conductor that I have connecting to the bottom of the tube means that the choke actually sits below the end of the pole. I’ve either got to move the pole up a little, which means moving the bottom U-bolt, or cut some of that centre conductor off, which is likely what I will do.

However, I’ve got a bigger problem.

I wasn’t paying attention when I put the 10mm tube inside the top of the 12mm tube. I’ve got the end tat I sawed at the top. Burrs and all. The 10mm tube is not as far down as I need it, and it’s now stuck. Nothing I can do will get it out. I’ve made a right mess trying to use multi-grips to move it. I suspect the best thing to do is to get another couple of bits of tube 😦

Relief

Given that I was resigned to buy more tubing, I decided to cut the 10mm tube off as I still had sufficient to put in the other end.

DSC_0144

So I’ve turned the 12mm tube upside down and you can see the nice mess I made trying to get the 10mm tube out. I’ve also still not shortened that 5cm length of coax inner conductor.

DSC_0145

As you can see I still couldn’t get the 10mm segment in quite as far as I wanted.

DSC_0146

This is the mess from the end that I cut out that is now at the top. I bought a rubber foot to put on the top but not quite sure what I’ve done with it just now.

Anyway, I leaned it up against the house and fired up the antenna analyser.

It looks resonant (SWR 1.01:1) around 27.300 MHz, so still a bit long I may need to cut off some of the top.

However it’s still giving better than 1.5:1 on 28.490, so I’ll be giving it a work out tomorrow when things open up a bit.

An interesting aside. I’m also seeing around 1.2:1 on 12m!

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