It started as a self-test project; create my own antenna as an experiment in learning some basic theory and dusting off some hand skills.
I started off with the following main components:
In addition, I had an old outdoor heavy-duty junction box which I intended to cut up to make the vertical part for the copper driven element. I also procured a 200mm length of aluminium tube, 20mm OD and 10mm Inner core, to use as the mast connector in conjunction with a bracket plate.
I cut the corners off the aluminium plate where the ground plane elements would go. This was not done scientifically, I just used a 45 degree square and chose a random 15mm length as the amount to cut.
I marked out the centre and another dot where the mounting pole would go.
I then used a step cutter to drill out the centre hole for the SO239 centre element. This would need to be a snug fit and also prevent the centre element from grounding out on any of the aluminium plate.
Note please the professional setup of using cheap clamps and old rotten outdoor tables! I do not have a workshop!
Next step was to mark out the screw holes for the SO239 connector. I used my square just to keep the screw holes parallel to the edges.
I drilled 4 3mm holes for mounting the SO239. I found some M3 bolts and nuts online. I’d cut down these 4 to prevent any issues when connecting the PL259 later, but they were bought to be long enough for the other elements.
Next step was to mark up the ground plane elements.
I’d previously gone online to a calculator and had a measurement of around 550mm for the 4 ground plane elements. I cut the aluminium bar to 600mm to give a little room for adjustment.
I allowed 35mm on the plate, and set the holes 15mm apart and 10mm from the end.
The next (fatal) step was to drill the 3mm holes. Into 4mm aluminium bar. With no post drill or vice.
Drilling by eye with no proper equipment was a gamble, however it appeared to pay off. I drilled the holes in the 4 lengths of bar.
Remember – 3mm holes in a 4mm aluminium bar…
The next step was marking out lines on the plate where the ground planes would go. As each one was drilled by eye, I numbered the ground planes and the plate as I went, to ensure each one fitted correctly.
I drilled all 4, then fixed them with 3mm bolts, spring washers and nuts.
I didn’t take a picture between the one above and this one. I had a plastic junction box which was no longer needed, so I cut a section out of it to form a right-angled section 100mm wide, then cut two shoulders on the upright section to reduce wind resistance, and cut a small section out at the bottom to accommodate the centre piece of the SO239. I angled the base to fit the ground planes, but I didn’t use precise measurements. I’d need to drill holes into the plate to fix this upright section.
The idea of this part is to provide a fairly rigid but insulated section for the driven element. The box I used was 4mm thick so I felt it was robust enough to support the upright, while also having an element of flexibility in high winds.
I used 3mm saddles to fix the copper tube to the upright element, and bolted the upright to the plate. At this point I’d only fitted the upright with two bolts, but I’d be doubling up later.
I’d factored in 3 saddles on the driven element, but due to a depleted stock of bolts I only used two.
This is how it looks from underneath. Still to come was the mounting pole and angling of the radials.
Next, I realised my mistake. I’d ordered a mounting tube with 10mm inside diameter, and M10 bolt! Obviously this wasn’t going to work as the tap needed to thread the tube would need to be 12mm…
I drilled and tapped a hole to insert a grub screw type affair, but it wasn’t going to be good enough to support it long term. I order up an M10 anchor bolt, which worked really well and locked into the tube very securely.
I also used a pair of pliers to hold the ground plane elements, and bent each one carefully to 45 degrees.
Almost at the end, the next step was to connect the copper tube to the SO239. I soldered some copper wire into the tube and then to the SO239 centre connector. At this stage it was ready for initial testing.
I add here – at this stage I’d not taken my Foundation, so I was able to listen to channels, and managed to hear a lot more than with a whip antenna.
Happy that it would do the job I then used a hot glue gun to seal the SO239 soldered element, and waited for my exam date to come around.
The sealed element. I also pulled the top of a 701 whip off and stuck it onto the top of the copper tube.
I took my Foundation and passed, then waited for my certificate to arrive. With people saying theirs arrived in 4 days I was hopeful, but nope, it took 8 days! Finally, Ofcom-registered and with my new M7 callsign, I connected up my SWR meter…
on 144MHz I had an SWR of 1.04:1 on a 25m run of RG213 at 1w.
On 440MHz my SWR was 1.02:1. I was happy with this. To recap, I used a 500mm driven element and 600mm radials.
The final part of this tale is a sad one. I had a pole in the garden as a staging place before deciding where to fit the antenna. I lifted it aloft on an evening where the wind decided to pick up.
Within about 30 seconds of the antenna being up in the air about 20ft, a tree got blown heavily, and it bent over and a large branch caught two radials. You remember, I’d drilled 3mm holes into a 4mm bar of aluminium… yep, two radials simply snapped off.
I figured I’d need either thicker bar (would it bend ok?) or, and the route I took, to congratulate myself on a good test, and get a Diamond vertical antenna. I chose an X-30 to maintain peace an harmony with relatives and neighbours…
The moral of this story? Have a go at building your own antenna, but make sure you factor in all aspects of sizings!
Love this! Well done for having a go at least!
Thanks Phil! Was a shame but I had fun 🙂