Simple Collinear

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hertzian

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Has anyone tried this:

The Simple Collinear

It looks very interesting to use very fat and very thin radiators instead of trying to cut stubs or coaxial phasing lines.

Essentially it looks like all you have to do is use say 1-inch tubing with thin #30 or so wire.

Obviously this thing will need a radome or some other kind of support, taking into account the typical lowering of the resonant freq with a radome.

Or, hang in the attic if you have to - to get anything reasonable for me, looks like VHF would be out, but maybe for UHF and above? I just might have to give this a shot!
 

hertzian

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Well, whaddya' know? It works - at least when modeled in EZnec. I haven't built one yet.

I'll have to post the pics of the modeling when I get access to my laptop again.

For VHF, I just modeled a simple dipole made with 1-inch tubing. Then, I placed #30 sized wire cut a bit longer than usual for another half-wave (about two inches longer) attached to the top dipole element. Attached to the top of that skinny wire was another half-wave of 1-inch material cut to the usual formula. Bingo - a simple collinear. Repeat as needed.

While there is significant radiation at about 45 degrees, the #30 wire preceeding a fat tube brings a very low angle (about 5 - 6 degrees) lobe at the horizon. Once the first half-wave becomes fat, ie using say #10 gauge wire, the antenna is acting much like a long-wire with most of the energy pointing up at 45 degrees. The low angle lobe is there, BUT it doesn't have any significant gain, making the whole thing moot if you don't use the skinny wire. However, if you get that thing up at about 20 feet or more above ground, you can use larger wire than #30 and get away with it.

Anything larger than about an inch diameter for the fat elements obviously works, but the benefit isn't as large as I thought.

So with careful pruning, this works in software at least. I haven't modeled UHF or 800 mhz with it yet. Standby for modeling pics....
 

hertzian

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Plots for simple colinear

Well, here we go. Included are three modeling plots based on using #30 inch wire as the phasing line, and 1-inch tubing for the half-wave radiators. The thin wire was cut two inches longer than the standard half-wave formula 468/f mHz. Antenna up at 20 feet and is just a standard dipole, with one other 1-inch diameter half-wave radiator separated by a thin #30 wire.

You can see the minimized current distribution on the thin-wire segment, allowing the upper and lower half-wave to get some power down into the lobe at the horizon. Not bad for just mixing fat and skinny. :)

Also included is a model showing how the low-angle lobe is severely attenuated if you DON'T use a thin wire. In this instance, I used the same 1-inch material for everything. Not good, unless you really like a 45 degree angle. I forgot to move the cursor, so if you read the data, it shows 4.87 db but at the 45 degree lobe!

What was interesting is that if you increase the skinny wire from #30 to something a bit easier to find around the shack, like #18 speaker / zip cord, you only lose about half a dB gain. Nice! Yes, you can get that back by using 2-inch tubing, or just accept the loss.

So here's something to play with if you have some spare tubing and wire laying about, and some way to hang it.

I'm not sure what exactly the formula is for the extremely skinny wire, so I'll have to research that as I just used the example from the web page showing the thin element about two inches longer at 2M.
 
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