Super 58 Magnum. Homebrew 5/8 vertical started

[davev8]

I have started construction of my new 11 meter 5/8 wave named the Super 58 Magnum…or S&M for short… will have a 5/8 radiator and four ¼ wave horizontal ground radials, insulated from the mast and have a built in coax choke.
It is also going to be tested with the ¼ wave horizontal radial swapped out with steeply sloping 5/8 wave wire radials
The design I have come up with is down to the members of this forum
My thanks go to Marconi who recently model a 5/8 wave with 8 ¼ wave radials which show that they had very slightly less gain than just 4, hence its got 4
Marconi Perversely modelled a 5/8 wave for me with steeply raked radials a full 5/8 wave long and found the gain was promising but had very heavy CM currents on the mast and feed line
So hence my big insulator and built in choke
Also I thank W5LZ for some comments on chokes which made me decide 100% to have a choke
And Northern 35 for posting a link to G3TXQ choke charts
Progress so far
Looking at the Photos from the ground up you can see a length of 2 inch stainless pipe this will be the mounting point to clamp to my mast . in the pipe it has a fiberglass shaft bonded into it, This shaft started out as a 14lb fibreglass hammer shaft. Which I rapped with fiberglass matting and resin to increase the diameter to 47 or 48 mm to fit inside the stainless mounting tube and the radiator. Yes the radiator is going to be a huge 2 inch in diameter(hence the magnam moniker) tapering of to 1nch and a ½ (40mm) at the top…massive wind loading I know but the tubing is hi quality as it came from a portable scaffold system, although its thin walled at 1.6mm it is very springy when trying to bend it. The diameter, should help with bandwidth

Clamped to the fiberglass stub (hardly a stub its 3 feet long ) is the hub for the radials that I fabricated from stainless steel, the stubs are 16mm / 5/8 of an inch .I made it hefty as if I end up with the 5/8 wave 25 degree wire radials they may be used as guy ropes
The radiator as you can see is slid over the fiberglass stub to be clamped on, clamp not fitted as yet
The matching device is going to be the ring type, 1 end connected to the clamp that clamps the radiator on and the other end to the radial hub
Just below the hub around the fiberglass stub will be a piece of 4 inch plastic tube with the choke will be wound around , and the ISO socket mounted to the underside
Well that’s the progress so far .. I still need to find the stuff to make the ring, I will probably have to buy some 10mm solid aluminium bar for it
To get a sense of scale you can see in my hand a old 5/8 wave silver rod
Let me know what you think or any improvements that can be made

Dave

 

[NorthStar]

Looking good!!!!

 

[Marconi]

Dave, I think those models suggested collinear responses with a 5/8 wave radiator and slanted down 5/8 wave radials, but the idea needs to be tested...just like you seem to be suggesting here.

I'm not sure Eznec handles a collinear correctly.

Good luck and keep us posted.

 

[Marconi]

Dave, I think those models suggested collinear responses with a 5/8 wave radiator and slanted down 5/8 wave radials, but the idea needs to be tested...just like you seem to be suggesting here.

I'm not sure Eznec handles a collinear correctly.

Good luck and keep us posted.

Dave, if you're still interested: the reason for my statement noted above...is because the model does not have a reversing element that will fix the phase differences to be noted in the model I sent earlier.

Without some device that is able to effectively reverse the out of phase currents in the slanted down 5/8 wave radials the currents in the setup will not be in phase with the top 5/8 wave radiator. So, there should be little to no radiation from such a setup regardless of what the model shows. There is a local guy in Houston, that has said the setup will do exactly what my Eznec model shows and that he has physically tested the idea at his station. However, I visited him and he does have an Imax in his back yard, but it has no ground plane radials or wires that could serve as 5/8 wave radials.

At least this is the way I understand two radiating elements in series, one over the other, working as an effective collinear setup.

I admit the model shows it does work correctly, but the current phase is just as I would predict, out of phase, and I don't see how this setup can really work if this conclusion is fact.

Please continue with your project, but consider the possibilities.

 

[davev8]

well if the long radials work they work if they don't they don't, i have no ideas how to make them work if they don't work apart from insulating the mast and the choke which is part of the design to combat the currents on the mast and feedline that your models show.. it will not take to long to change them over..That was one reason i made the hub split so can be removed without dismantling anything in case i have a different hub for the wire radials, which i have decided not to do as other stuff will be mounted on the hub
Looks like with work constraints its going to be at least another week before i make any more progress

 

[Marconi]

well if the long radials work they work if they don't they don't, i have no ideas how to make them work if they don't work apart from insulating the mast and the choke which is part of the design to combat the currents on the mast and feedline that your models show.. it will not take to long to change them over..That was one reason i made the hub split so can be removed without dismantling anything in case i have a different hub for the wire radials, which i have decided not to do as other stuff will be mounted on the hub
Looks like with work constraints its going to be at least another week before i make any more progress

Dave, here is the model I sent you before, a 5/8 wave radiator and 4 x 23' foot slanted down radials. In order to show you why I think this model might have flaws in the results, ie. trying to respond like two stacked 5/8 waves as collinear which the results seem to indicate.

I had a thought that this design would mostly be radiating from the radials and the radiator would only be helping a little by acting like a load rather than a radiating radiator.

So, I took the model and removed most of the radiator making it 4.8" inches long rather than 22.5' feet long, see wire #1 in the second model below. I wanted to see if the gain would still show up on this butchered up antenna...and it does as you will note here:

View attachment Dave's 5_8 wave ideas with 23' radials..pdf

The increase in gain noted by this model with the short radiator is probably mostly due to a substantial increase in the SWR, from about 13.0:1 for the original model to over 100:1 SWR for the shorter model. The pattern for the shorter model has changed for the worse, but the gain is still indicating a big gain...like we might expect with two vertically stacked collinear 5/8 wave radiators.

Just be aware that your test idea may not respond like the model is suggesting.