Posted by
k0wa@swbell.net on
Nov 16, 2007; 8:51pm
URL: http://elecraft.85.s1.nabble.com/Mathematically-challenged-tp366490p366491.html
I am a little confused here as to what you want to build. A two element beam or a two element vertical array. Then you go on and site information about making a "beam."
These are two different animals.
So, here are the calculations.....in feet
1/2 wave dipole - 468/F or 468/14.2 (20 meters) = 33.2 feet. Now that is a half wave so to get a full wavelength just double the number of 66.4
According the all the books, the director should be 4%-5% longer. So all you have to do is take 33.2 times 1.05 which comes out to 34.8
To figure the spacing...that the full wavelength number and take it time what you need....lets say .2 Then you get 13.28 feet. Now there is a lot of wiggle room on the boom....you might want to model this before you actually build it, but that is a starting place.
So, now if you are looking on a vertical on 20 meters....well that is a different animal all together. You could use a parasitic vertical but that would be hard to turn. In fact, the two element vertical for 20 meters would be stationary or you would have to have a big wheel or something. You could also use two quarter wave elements on 20 with some pretty good counterpoise wires under them and then space them a halfwave apart...33.2 feet. Then you would feed them in the middle with a coax "T" connector. That would give you a basic figure-8 pattern. As you can see it would be stationary, unless you have some pretty good real estate....and some way of turning it.
So, I wonder if you could clarify what exactly you are looking for....
Lee - K0WA
In our day and age it seems that Common Sense is in short supply. If you don't have any Common Sense - get some Common Sense and use it. If you can't find any Common Sense, ask for help from somebody who has some Common Sense. Is Common Sense divine?
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