2x4 beam antenna?

[longhaireddwb]

I think I remember someone posting a picture of a beam antenna that was made with boards and strung with wire. Could someone help me to find this? And do you think it would work with 20 meters? And how to make it if it would work?

I just got an IC-730 and I have no antenna. I can string up some wire on the roof of the two story apartment I live in but how much wire? How long should the four sides be? Should I make it a square or rectangle? Should I bring both ends of the wire to the coax that will feed it? One to the shield and the other end to the center lead so it makes a complete loop? I'm really in need of some help in getting this started correctly. I've got just over 400 ft of 12awg wire to use if I need it. Should I just run two pieces of wire in oppisite directions and connect the coax in the middle?

I remember the numbers 468 / the frequency for a half wave length but to put it to use I'm lost. I have my general lic and want to put it to use. I have a 11 meter a-99 on a mast and with the tuner I'm getting 20 meter signals but cant make contact.

Help a newbee get started!

 

[W5LZ]

There are several 'magic' numbers that are fairly easy to remember for wire antennas. They result in a slightly too long antenna, but that's much better than a slightly too short of one. For a 1/4 wave length, the 'magic' number is '234'. For 1/2 wave it's '468'. And for a full wave it's '984'. You'll see that those 'magic' numbers are not a strict multiplication of each other. That's because they factor in a velocity factor for wire sizes of average use.
Pick one of those 'magic' numbers for the 'size' of antenna you want and divide it by the frequency in Mhz that you want the thing resonant at. At that point, adding an extra foot of wire just makes making connections much easier and not coming up too short. Or maybe 2 feet just to be safe? You'll have to do some trimming to tune it anyway, so a little extra will come off, but so what, it's just easier that way.
No matter which particular 'size' antenna you use, don't expect to end up with a 'perfect' 1:1 SWR. That happening is almost a miracle, just too many factors that affect things. If it's 1.5:1 or less, it's certainly good enough that your '730 will never know the difference.
If the first antenna you make isn't quite what it should be, do it again but pay a little more attention, sort of. With 400 feet of wire, and a 20 meter 1/2 wave dipole something like 33 feet long, you've got a pretty good chance of getting it right with more than 10 tries at it! Or 5 tries at a full wave. And I really doubt if you'll need more than one try if you're sort of careful, you know? Make it too long then trim to size is a pretty 'normal' way of doing it.
Have fun.
- 'Doc

 

[longhaireddwb]

So are you talking about making a loop with that amount of wire or stringing it straight out from one end of the building to the other? Of course I'm talking about a horizontal wire not vertical.

If a loop, would that number be the total length of wire (plus the extra for tuning) and would all four sides need to be the same? Would a square or diamond or triangle or rectangle shape be better?

If a two straight runs of wire in opposite directions with the coax connected in the middle would this amount of wire be the total length or that amount in both directions?

Is there a benefit in doing the full wave compared to the half wave?

I'm about to start pulling my hair out!

:headbang

 

[longhaireddwb]

Oh, and what about this beam made out of wire? Could this be a bonus to build being its in the shape of a beam?