Building a vertical antenna with traps

Last week I bought a few cheap aluminium pipes and decided to build a discrete vertical antenna for my post stamp backyard. The goal was to make something that looks a little bit more professional than a cobweb of wires, and at the same time support the 10, 15 and 20 meter bands. If that wasn’t challenging enough, I didn’t want the antenna much taller than 3 meters in height.

In order to accomplish the above in such a short antenna, I added two traps for 15 and 20 meters. These traps were made with stubs of RG58 coax that was wound around a 30 mm PVC plumbing pipe. I did three turns for the 15 meters, five for the 20 meters, and I did the loop trick where the screen on one end loops back to the center lead on the other end.

I’ll happily admit that, apart from a tape measure, the traps were not metered or measured in any other way before, nor during, the build. I thought “this looks like it might work” and decided to go for it. Fine-tuning could be done later.

The radials are just three 120 cm elevated telescopic rods, and a 20 meter long wire that runs across the hedge. They are definitely subject to change shortly.

Right now the antenna is mounted on a camera stand, fairly close to the ground. My goal is to put it up in the tree to the right, which is maybe 15-20 meters tall, but the realistic install height may be around 10 meters for the base of the antenna. Before I start climbing I need to be sure the antenna is working fine.

The current version of the antenna is working fairly well, and it even brought two surprise bands with it on the way. The SWR is as follows, no ATU:

Band
20m
17m
15m
12m
10m

SWR
1.6
1.2
<1.1
1.6
1.5

The antenna is also quite broadband. The measurements above are for the entire band, from start to end.

I’m going to try and tune this antenna a little further, and see if I can lower the SWR on the 20 meters (and maybe 12) a bit more, but knowing a trap antenna is far from ideal, this may be as good as it gets.

Hopefully, by adding a little height to the equation, this antenna will improve further and suffice for the higher bands once the spring sets in for real. 10 meters is still on fire from time to time, I picked up VK3 on FT8 yesterday morning, using this antenna.

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