I am looking for some assistance with building my own dipole for CB frequency. I have not been able to locate a website that provides me with picture details. I have the copper 12 guage wire & a 1:1 balun with the isolators. Knowledgeable & experience assistance would be helpful. Thanks
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5/8 Wave Dipole CB Radio
- Thread starter radio59
- Start date
don't build a 5/8 as feed point impedences are very far off without a matching network
do a 1/2 wave using this calc KWARC Dipole Calculator
tweak from there
do a 1/2 wave using this calc KWARC Dipole Calculator
tweak from there
59, the site that Bioman linked us to is very close to on the money in length for a 1/2 wavelength. He is right about staying away from a 5/8 wavelength in this case. Your using wire, so consider using longer than needed and looping the extra wire thru the insulators on the ends and wrap it on it-self to make the working length. This way you can adjust the length over a range of frequencies and it may help you avoid having to add wire or rebuild if you go too short.
Someone will provide pictures soon and you should be good to go. They are very simple to build. You may need to give some thought to how you will support the antenna and what to do with the feed line, which needs to exit the wire at 90 degrees for at least a 1/4 wavelength or more.
Thanks, What would a matching wave consist of? I would like to build my own antenna, because I purchase a Imax 2000 from a friend and the swr is off the chart about 3:1. I believe I should be able to find some info on adjusting the swr, but it's something about building my own. I have plant hanger with a pulley and some rope that I pickup from a amateur consignment shop in Minnesota. I will use the calculator to see what I come up with. Thanks again
Marconi, thanks I am trying to be low profile with my setup. Because somethings I didn't do right in regards to my neighbors. So I felt it's my responsibility to do it right and setup something that will not cause any problems. As much I like this hobby I still want to talk on SSB with just a simply dipole antenna perhaps a 100 watts or so. No more quads and yagi's they draw to much attention in the suburbs. Well thanks again
Those antennas are a flat match in most situations right out of the box, something is wrong.
Agreed.
Easiest antenna in the world to put up and operate is the IMAX. Right out of the box - they are factory adjusted. If you messed with the tuning rings at all - then you can bet it is out of adjustment. Mounting any antenna too close to a large metal object will give a bad SWR too. If you still have your IMAX; I would get with a friend that has some radio experience and see if he can help you get it set up right.
A dipole - which might be stealthier that an IMAX - is either a horizontally or vertically polarized antenna (the IMAX -IMO- is still a pretty stealthy antenna - compared to many ground plane type antennas). If a dipole is set up horizontal to the surface of the earth, it will be weak sounding to most of the locals you might talk to that use vertical antennas. Because a horizontal dipole is 90 degrees out of phase with a vertical antenna. That's just radio physics.
Now, if you were to build a vertical dipole - that would be a horse of another color. That could work. Horizontal dipoles work best when skip is in - or if someone else - locally - has a horizontal dipole as well. A vertical dipole will also work when skip conditions are present; but will have the added bonus of sounding strong with locals that are probably using a vertical antenna as well.
If you have an IMAX: I would DEFINITELY work it...
I think they most generally come factory tuned, and the rings are pretty much centered. The only thing to do it to put it up on a test mast and play with the rings, but it is a pretty forgiving antenna overall.
With a typical horizontal dipole, the feedpoint should be pretty nearly directly over the shack area, so the feedline hangs away from the antenna at as close to a 90° angle as possible. That's a necessity, especially when direct-feeding with coax.
If you have a VERTICAL dipole, the feedline still has to get away from the antenna at a 90° angle. At VHF and above, this isn't too hard. At 27 MHz it becomes more of a problem.
You've been given the dimensions (or how to determine them). You don't need any pictures; the dipole is the basic antenna, on which virtually all other resonant antennas are based.
Cut it a little on the long side. Attach center insulator and end insulators. Attach coax to center. Attach non-metallic rope or cord to ends and hoist it up. Determine resonant point and determine how much to shorten. Lower it back down and shorten it equally on both sides. Raise it back up and note the change. Take lots of notes.
Sounds like a lot of work, and it can be. Every installation is a little bit different from every other one, so there's no absolutely perfect length that anyone can predict over the Internet. Experiment! It's the one area of radio where you're free to let your imagination run wild. Try something - see if it works. If it works, improve on it. If it doesn't work, figure out why and fix it.
If you have a VERTICAL dipole, the feedline still has to get away from the antenna at a 90° angle. At VHF and above, this isn't too hard. At 27 MHz it becomes more of a problem.
You've been given the dimensions (or how to determine them). You don't need any pictures; the dipole is the basic antenna, on which virtually all other resonant antennas are based.
Cut it a little on the long side. Attach center insulator and end insulators. Attach coax to center. Attach non-metallic rope or cord to ends and hoist it up. Determine resonant point and determine how much to shorten. Lower it back down and shorten it equally on both sides. Raise it back up and note the change. Take lots of notes.
Sounds like a lot of work, and it can be. Every installation is a little bit different from every other one, so there's no absolutely perfect length that anyone can predict over the Internet. Experiment! It's the one area of radio where you're free to let your imagination run wild. Try something - see if it works. If it works, improve on it. If it doesn't work, figure out why and fix it.
with a 3:1 swr on the i max it sounds to me as if the fault is in your coax or plugs,probably a dry joint in the plug or possibly a stray strand from the shield shorting,anoher possiblity if cable is old is its had water in it through lack of waterproofing.
if the antenna was faulty you'd most likely get an off the scale swr reading or an intermittent reading if it had a loose connection inside.
Radio59, I don't believe you'll find a point moving the rings on an A99 or an Imax 2000 that will show you a 3:1 SWR in the CB bandwidth---assuming that the antenna is working as it should.
You may have a problem, but it is not a tuning problem.