Building a dipole - tips?

[Turbo T]

I'm wanting to try my hand at building a dipole to work on a 40 channel CB radio. I did a google search of this and have gotten some conflicting info in referencing the length of wire, how to build it, etc.

I've read I can build one from speaker wire. I have some old speaker wire sitting around. I also have a 6 foot piece of RG8X with an amphenol connector on it. Perhaps I can add the speaker wire I have sitting around on to this...?

I've read the dipole needs to be 17 feet long, I was thinking they were supposed to be 18 feet long...?

Not to mention is that 18 feet across? Or is that 18 feet total per side, from edge of dipole to where it meets in the middle to form the tee?

I also am confused on when the dipole is spread out in the "T" pattern...if one side Of the T will be the hot side and the other side is the ground side?

Some illustrations of a "building a dipole for dummies" would be a real help.

Thanks in advance.

 

[BOOTY MONSTER]

the wire coming of the center conductor of the coax is the hot wire . the wire coming off the shield is the ground . if you're installing it vertical (up and down) keep the hot/center wire up top and the ground/shield wire on the bottom . if you're horizontal (side to side) it doesn't matter because it will tx & rx the same off the sides with reduced performance in the directions the ends point to .

as for length , i wouldn't cut it to some someone elses perfect length for their location/installation . id make each side 110 -112 inches long and use a swr meter to tune it cutting the same amount off each end as you go .

 

[Quiksilver]

YouTube - ‪Make An 11 meter dipole (Short)‬‏

 

[HomerBB]

Horizontal

Vertical

It will be roughly 8' 7" each side, but can vary. Make it 9' per side, and bend back the wire equally on each side until you get the SWR correct. Yes, the center conductor is on one leg/side, the coax braid on the other leg/side.

Enjoy yourself.

 

[C2]

Don't get confused and think that RF ground is the same as electrical ground.

A dipole is a balanced antenna and you will get the same RF burn if you touch the end of either wire (hot or cold). The wire ends are the high voltage points, the center feed is the high current point.

The illustrations are good. I have a dipole as well as a full-wave loop. I like the loop because it is "grounded" and provides much less static noise, so better signal/noise ratio.

 

[Turbo T]

Thanks for the responses. It really helps clear up the confusion.

Now if I may ask does the dipole need to be bare wire to radiate?

And you say the ends of the dipole should be 9 ft long each....what about the center wire...is there any particular length it needs to be?

One last thing....what did you use for insulators for the middle of the tee?

 

[Simon004]

Now if I may ask does the dipole need to be bare wire to radiate?

No, the only difference you will notice if you use insulated wire is that the antenna will be a little bit shorter (but only a few inches).

And you say the ends of the dipole should be 9 ft long each....what about the center wire...is there any particular length it needs to be?

Not sure what you mean by "centre wire" tbh

One last thing....what did you use for insulators for the middle of the tee?

You can use almost anything that is an insulator, personally I keep the families old toothbrushes everytime we change them, chop off the brush end, and drill a few holes in the handle for the wire to pass through and use them for dipole insulators.

 

[W5LZ]

I think that "center wire" is the feed line. If so, it needs to be long enough to reach from the antenna to the radio. A little extra certainly doesn't hurt, just allows you to move stuff around more.
- 'Doc

 

[Turbo T]

Yes, the center wire is the feed wire off the PL259 before it splits.

Well I got the dipole together. it receives so-so but it doesn't radiate as my SWR's were waaayyy high....into the 3's!

This is my first time so i'm sure there's a flaw in my design, perhaps someone can please point it out?

First things first. I used insulated wire in the build. Both pieces I cut to 110 inches long.

I then crimped the ends of the wires to the coax. I ran one wire to the center wire and the other to the ground.

When hung up horizontally it forms a "T". Or looks like the thong on a chick. :drool:

Now I didn't have any insulators...so on the middle I just made triple sure the ground wire and the center hot wire on the coax/dipole did not touch.

When i hung up the dipole for a test, I tied small knots in the ends of the insulated wire of the dipole. I hung the ends up on the house outside, one against a hook on the siding, the other on a hook under the roof overhang.

Maybe I should cut off 2 inches from either side of the dipole?

Thanks in advance.

 

[Robb]

Suspend the ends of the dipole AWAY from any object. About 3 ft or longer should be enough. Use rope or nylon fishing line, but keep as much space around the antenna as you can. Check the overall length of the dipole; it should be close to 17 ft 4 inches. Each side should be equal in length; it helps a lot.

It doesn't have to be shapes like a "T" either. It will work very well as an upside-down "V" too. About a 90 degree angle or wider will work. This will make the antenna more omni-directional (means it will transmit and receives in a 360 degree/circular pattern; whereas a "T" dipole is bi-directional).
In fact; the upside-down "V" is one of the most popular way to mount it.

Keep the ropes holding the wires fairly taught.

If the SWR is higher on ch 1 than ch 40; then it is too short.
If the SWR is lower on ch 1 than ch 40; then it is too long.

Just sayin . . .

 

[W5LZ]

You've started in the right direction, now you just need to get a bit 'closer'. That usually means 'trimming' the thing to -the- right length for where you have it hung. I think you'll end up much closer to 8 1/2 feet per side, give or take a bit. Once you get the SWR under a 2:1, change lengths by smaller increments. Also no need to cut anything off, just fold it back onto it's self, wrap it a few turns on it's self to keep the length. You also have to 'trim' equal lengths from both sides, not just one!
All things considered, I doubt if you will get a really low SWR. If it get's to 1.5:1 or less, that's certainly good enough.
Have fun.
- 'Doc


(That "folding it back onto it's self" thingy means that if you go too far, you won't have to solder length back. Just un-fold a little bit.)

 

[BOOTY MONSTER]

"I used insulated wire in the build."

when you fold the wire back to shorten it's over all length , the section that is folded back over itself needs to be bare wire . i just cut mine when i made it out of speaker wire .

 

[hotrod]

sorry im not much with building this stuff. but i can say ya can use any wire ya
got laying around. gotta local here that made a rotatable dipole outta pcv pipe
and mounted horizonally .and he talks skip /locally pretty good .as long as there
on horizonal antennas.

 

[wavrider]

DIPOLE AND INVERTED V VEE DESIGN AND CALCULATOR

Good link with formula's and pictures.

I also prefer to use a 1:1 Current balun at the feed point, makes for a more efficient antenna.

 

[W5LZ]

Booty',
No, the wire used doesn't have to be bare for that folding back thingy. Insulated wire will behave the same as bare wire for that.
What's the best wire to use? Whatever you happen to have enough of that will support it's own weight and the feed line. You can even mix sizes with no problem. The only 'problem' with that size mixing is making good connections. Soldering the mechanical connection is a good idea. No particular benefit in using huge size wire unless you happen to have a bunch of it. A typical size is 14 gauge, there's usually more of that around than most other sizes. Hard-drawn copper wire is also a good idea, it doesn't stretch as much as the other kinds. But, if you allow for that 'stretching', soft-drawn works just dandy too. something the length of a 10 or 11 meter dipole just isn't gonna stretch much, and if it does, just do some more of that 'folding back' thingy.
HF dipoles may be 'rocket science' but it's more of the bottle-rocket variety than the Atlas/Saturn sized rocket...
- 'Doc