maybe a stupid question but, has anyone messed with dual base antenna's, 2 verticals or a vertical and a horizontal that receive and transmitt at the same time. is it something that would be a total waste of time?? what would be used to combine them and match them back to 50ohm?, just wondering this after seeing some of the antenna switch's that have selectors for A,B and A+B for a selection?
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dual base antenna's?
- Thread starter camaro1
- Start date
Would it be a waste of time? The best answer is "That depends". It is hard to say for sure without knowing what your intentions and goals for such a setup are.
The DB
You could certainly use phased antennas like that at a fixed station. I'm sure that it's done on other bands, not sure about 11 meters though. The simplest way of doing it would be to simply switch in an additional electrical 1/4 wave in one of those phasing 'legs'. That'd 'switch' direction by 90 degrees.
- 'Doc
- 'Doc
Without getting into a big 'to-doo' about it, the information on that site isn't exactly how it -has to be- done. There are a lot of variations in the separation distances and not just what was quoted. 1/2 wave antennas do not have to be a 1/2 wavelength apart, not to full wave antennas have to be a full wave apart. Usable separation distances are not specific to the 'size' of the antennas. Those distances certainly can affect the 'shape' of the resulting radiation pattern, but not typically a huge amount. There really is a lot more to it than that. William Orr's Hand Book has a very good description of most of this, it's worth reading.
- 'Doc
- 'Doc
Separation distances are affected by the type of antenna (according to the models I've built/tested. I wouldn't try to give a rule of thumb for all types.
I always wondered about those super scanners so I built a model to test it and others I remember seeing.
With a modeling program you can test hundreds of variations quickly.
I like/use 4nec2 it's free and feature rich.
The link is a model I built to study/test the super scanner.
Change the .txt to a .nec and open with 4nec2 if you want to play.
http://ghz24.freeshell.org/antenna/models/elevenmeter/tri-beam.nec
There is a tri-beam (super scanner) with a mast ( the mast has a dramatic effect), a 4 element version and some phased dipole pairs in the same folder.
I always wondered about those super scanners so I built a model to test it and others I remember seeing.
With a modeling program you can test hundreds of variations quickly.
I like/use 4nec2 it's free and feature rich.
The link is a model I built to study/test the super scanner.
Change the .txt to a .nec and open with 4nec2 if you want to play.
http://ghz24.freeshell.org/antenna/models/elevenmeter/tri-beam.nec
There is a tri-beam (super scanner) with a mast ( the mast has a dramatic effect), a 4 element version and some phased dipole pairs in the same folder.
dual antennas a whipp'n in tha wind, lawd there ain't a country station station that I cain't tune in!!!! Yee haw!!!
I kicked around the idea of running two 8 element quads once. One at 1 wave length above the ground and the second one @ the second wave length on 2 separate towers about 50 meters apart. I had all the stuff to do it but never did. It seemed like a lot of work just for an experiment.
You can use two vertical antennas like two Imaxs, a99s, or Protons a 1/2 wave apart if you want both a couple of nulls in the 2 directions of a line drawn thru both antennas, and about 2-3dB gain 90 degrees (perpendicular) to that line.
To keep a 50ohm load you can use a 1/4 wave long (x the coax velocity factor, about 7' 2") piece of 75ohm RG-11 coax as an impedance matching transformer from each 50ohm antenna to transform them both up to 100ohms. Then you can parallel them back down to 50ohms by connecting both into a coaxial T connector which then connects to your 50 ohm coax from the radio.
You can use an identical set of 2'-3' long 50ohm jumpers from each antenna to it's 75ohm transformer coax so it will reach the T connector in the center.
This can be useful if you have a heckler about 90° off from the direction you want to receive, but rotating & stabilizing an 18' T-bar with 2 verticals would be quite a chore for a smaller rotor.
Setting three verticals into a 1/4 wave triangle can help eliminate 'picket fencing' since all nulls seem to disappear, but you would need to use a 100Ω 1/4 wave matching transformer from each antenna connected together in parallel to get back up to 50 ohms.
Two parallel verticals might be worthwhile if you need a reasonably deep null in one direction (plus the 2nd null 180° from it) plus a little forward & rearward gain, but three parallel verticals is without all that much in the way of returns for the investment of a lot of work & buck$, unless you simply must have the best omni around.
I ran stacked PDL2s back in the eighties! Eighteen foot apart at seventy two foot elevation. This is a great setup, being tight and a ton of gain.
I'm now running a PDL4 element.
If I have the room, I'd stack a pair of these puppies.
Nothing ventured nothing gained!!
Have fun.
I'm now running a PDL4 element.
If I have the room, I'd stack a pair of these puppies.
Nothing ventured nothing gained!!
Have fun.
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