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20 meter two elements

AE5RD

AE5RD

Reformed CB'er
May 4, 2005
136
1
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Ok I'm building a two element 20 meter full size beam. I can't find the spacing of the elements. One element is the driver the other a director. I think the spacing is about 13ft. Is that correct? I almost hate to ask on this forum but I just need some more information.
 

You may not like this reply, but here goes:

Make them any spacing you want. The SteppIr 2-element beam had 2 full size elements on a 5 1/2' boom! Yep, 5.5'!! Did it work? Sure did!

My question would be, "How long is your boom?" If its 12', then space them 12'. If it is 11' 5 1/4" then space tham 11' 5 1/4"! Yes, all of these dimensions work.

My second question would be, "What are you trying to accomplish with this antenna?" Are you looking for the maximum amount of gain with 2-elements; are you looking for a maximum front to back; what kind of bandwidth do you need? So many questions!

My final question would be, "Why do you want to use a driven/driver rather than a reflector/driven?

Figure out what you want and let us know. Maybe we can help you. Be prepared to tell us the diameters and exposed lengths of the tubing, the size of the boom, whether you are grounding the director to the boom, the size of the brackets, and what type of feed point you plan on using. At this point I'm assuming an insulated split driven element with a choke balun as a feedpoint, but I can be wrong.
 
antenna

I found this to be a good read. I like how it has a parts list. This antenna has been scaled down in size. I already have my full size elements and a 20 ft boom. Although I might try the smaller antenna I would like to finish the full size beam first, since I have gone this far. Oh I am using 3/4 aluminum tubing that steps down to 1/2 and then to 3/8. Yes I am split feeding with a 1:1 current Balun. I mainly want to see if I can increase my gain in one direction. My single element worked good and was directional somewhat. I just wanted to see the diffrence. I can go with a reflector and driven too. Which is better? Mind you this antenna is experimental and is not designed to stay up for ten years. I just have a fold down tower and it makes it easy to play with my antennas.
 
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let me get the full specs tomorrow it's getting late I'll post them tomorrow that way you'll know more about what i"m working with.
 
Typical element spacing is between 0.15 and 0.2 wavelengths with 0.18 being somewhat optimum. Slight changes will not matter all that much but may affect F/B or impedance a bit.
 
Which is 'better', using a reflector or a director? Either way, there isn't enough difference to really make a difference. Whatever difference there might be can usually be compensated/re-tuned to sort of 'even things out', "six of one, half a dozen of the other".
Ah, use a reflector. Saves you from having all those little bitty pieces of tubing laying around from the trimming of a director...
- 'Doc
 
If you want to get right down to it, with a simple two element yagi, the use of a driven element and a director will show slightly higher forward gain but it is very slight. The use of a reflector will yield a slightly better front/back ratio and again the differance is very slight.
 
Freecell that looks like an antenna that I can build. I think I might try. Easy and not too fancy. I like 20 meters the best.

I think I'll go with the reflector driven setup. Another Question. I am using a 1:1 current Balun to feed the drive element. Is that OK to use or does the impedance change with only two elements. I see all knds of matching systems and I must admit they don't seem to make sense to me. I am reading about some diffrent ways to match the driven element. I know I must seem like I don't know anything and lets just say I know some basics. Beyond that I won't lie I need to learn. I enjoy the challenge tho and the fun of making my own antennas.
 
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You are doing great!

A 1/1 current balun will work fine although not a perfect match to the feed line because a 1/2 wave dipole is NOT 50 ohms.

When you check SWR, you are checking the "match" of the FEEDLINE at the FEED POINT. You should check SWR AT THE FEEDPOINT, but that is not always possible. So, we check SWR at the other end of the coax. Here is the thing though, unless that piece of coax is exactly a multiple of an electrical 1/2 wave length at the specific frequency you are testing, then the reading at the feedpoint vs the reading at the meter, will be different. Why you ask? Because that piece of coax acts as a transformer and actually transforms the reading.

See, you learned something new today!
 

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