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Crackshot
Member
Username: Crackshot
Post Number: 69
Registered: 10-2005
| | Posted on Friday, November 18, 2005 - 10:04 am: | 
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I want to build a dipole. Question I have is the balun.
I see auction sites sells 1:1 and 4:1 baluns but I will build my own and not paying 25 bucks for a PVC pipe with caps and eye hooks.
What defines 1:1 and 4:1 baluns?
I was going to use a few ferrites around coax inside of tube when I construct it. Is a couple of ferrites do the trick for RF coming down the coax?
Should I run a ground off shielded side of coax inside balun to the earth?
Thanks |
Bruce
Senior Member
Username: Bruce
Post Number: 3229
Registered: 9-2003
| | Posted on Friday, November 18, 2005 - 12:29 pm: |
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crackshot
1:1 balums are used for center fed ( single wire ) dipoles 4:1 are used for dipoles using 300 ohm ( or " folded wire " ) dipoles.
For a 1:1 used ferrites or just coil 6-8 turns of coax up at the feed point. |
Crackshot
Member
Username: Crackshot
Post Number: 71
Registered: 10-2005
| | Posted on Friday, November 18, 2005 - 1:19 pm: |
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thanks Bruce. That helps a lot.
How many ferrites should I use? I was going to put them on the cable inside the balun.
Maybe 2 or three of them? |
Wildrat
Intermediate Member
Username: Wildrat
Post Number: 333
Registered: 12-2003
| | Posted on Friday, November 18, 2005 - 5:38 pm: |
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Crackshot let me know how you do because I'm going to build a Yagi and a dipole at some point and I'dlike some feedback on how it's working.
Wildrat |
Vanillagorilla
Intermediate Member
Username: Vanillagorilla
Post Number: 325
Registered: 4-2005
| | Posted on Friday, November 18, 2005 - 11:08 pm: |
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For what its worth I built a simple dipole a year ago to get "re-started" on the cheap.
I made it from coated solid strand copper wire and some old RG-58 Coax soldered to an SO-259.
I tossed it 15ft into a pine tree and secured the inverted "V" ends to the lower branches with small bungie cords. Ran that OLD (shame on me!) RG-59 into the basement dialed in SWR and talked 15mi on my first shout with an old 3watt mobile Realistic.. NOT with the strongest signal mind you but it worked!
Had I taken the time to do it all right I know it would have been better but HEY! IT GOT ME ON THE AIR and I was thrilled to build it myself.
In the middle of a double bazooka dipole for inside the attic...just another option for the antenna switch..
Still say that homebrew 30min antenna was quieter than my Antron99 is today!
Do a search on the net for "double Bazooka dipole". Great "Do it yourself" project for a rainy day.
Hank |
Crackshot
Member
Username: Crackshot
Post Number: 74
Registered: 10-2005
| | Posted on Saturday, November 19, 2005 - 12:09 am: |
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Thanks for all input. I finished building balun.
I have pics and need to post them when I figure it out.This BBS is not the most user friendly like some of the others I frequent.
Too tired tonight.
What should I make #14 copper wires?
102" for each side on 11 meter band?
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Crackshot
Member
Username: Crackshot
Post Number: 75
Registered: 10-2005
| | Posted on Saturday, November 19, 2005 - 10:35 am: |
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Ok calculated lenghths. 11 meter middle of band should be 8.6 feet center to end each leg.
I have 7 ferrite cores and looped coax 4 times through them. This will go in 2 inch PVC.
Will they work? Do not know, Figured it could not hurt!
I am installing all components after installing the SO239 connector on bottom cap.
I wound and used up all 20 feet of coax with the eye screws installed.
I added zip ties on each side to secure coax after winding up tight.
We will see if it works now!
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Crackshot
Member
Username: Crackshot
Post Number: 75
Registered: 10-2005
| | Posted on Saturday, November 19, 2005 - 6:59 pm: |
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Well installed it and sad to report total failure.
Has over a 3:1 SWR and can't even pull in stations that are close.
I am tearing it down tomorrow and sticking with my antron.
This is the last time I waste my time and money on something like this again.
Thanks for all the help anyway.
The good side is, I will use the cable I routed into houes for a scanner antenna! |
Wildrat
Intermediate Member
Username: Wildrat
Post Number: 340
Registered: 12-2003
| | Posted on Saturday, November 19, 2005 - 9:34 pm: |
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I would not give up crackshot. Dipoles are not that hard to build. Look yours over and make sure you did everything right. Did you do a Google search on building dipoles. There is a lot of info out there. I am going to build one, I have downloaded dipole calculators, and other things like plans etc. Don't give up so easily. I would look at my Balum a little closer. It could just be a stray shield wire causing your problems. You don't want to run your radio with SWR like that, and definetly don't put no power to it, not unless you need a new amp or transistors at the least.
Wildrat
CEF674
When I build mine I will build two,one for 13 and then another for that freq much higher to talk skip. |
Wildrat
Intermediate Member
Username: Wildrat
Post Number: 343
Registered: 12-2003
| | Posted on Saturday, November 19, 2005 - 9:58 pm: |
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CC,
here is a link to one balun construct on the cheap from a Google search.
http://www.arising.com.au/people/Holland/Ralph/CMBalun.htm
Wildrat
CEF674
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Bruce
Senior Member
Username: Bruce
Post Number: 3230
Registered: 9-2003
| | Posted on Saturday, November 19, 2005 - 10:44 pm: |
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Hummmm
It should work check for a bad connector or a short |
Wildrat
Intermediate Member
Username: Wildrat
Post Number: 348
Registered: 12-2003
| | Posted on Sunday, November 20, 2005 - 11:33 am: |
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Crack shot I put another link on here to another balun. I guess it did not meet Copper rules. Any way it said not to just roll up a bunch of coils and tie or tape them together. It described the same problems you are having. It said something about not letting the wires overlay each other and some other technical stuff. It said to use a piece of pvc wrap it around it, and make sure the ends don't touch and this and that. I'll look for it again and put that section in a post.
Wildrat
CEF674 |
Wildrat
Intermediate Member
Username: Wildrat
Post Number: 349
Registered: 12-2003
| | Posted on Sunday, November 20, 2005 - 11:39 am: |
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This is the page without the balun picture.
Wildrat
Build an All Band HF Air Core 1:1 Choke Balun
THE "UGLY BALUN"
A balun's purpose is to allow connecting a BALanced load (e.g., a dipole or driven element) to an UNbalanced line such as coax, thus the name, Balun.
In transmitting antennas, this is accomplished by presenting a high impedance (resistance), to RF currents flowing outside the coax shield. This forces currents in each side of a driven elements to be equal. This is especially important in beam antennas because it prevents distortion of the beam's pattern caused by unequal currents in the driver(s). In a simple dipole, the balun assures that the dipole, and not the feed line, is doing the radiating!
When you connect center fed antennas, like dipoles, V's, triangles, yagis, rhombics, loops and so on, to coaxial cable, unless care is taken, it is not difficult to end up with feeder radiation. Not only can the loss in power be quite significant, but the radiation characteristics of the antenna system will also be seriously compromised.
In laymen's terms, it won't be what you are expecting from the pattern of your antenna.
As the feedline becomes part of the antenna, currents can flow from the line into the mains and on TV cables, metal masts and yagi booms, causing a variety of EMI problems that can be very difficult to trace. Frequently these problems are simply due to unbalance - and the solution is the humble balun!
If an antenna system is fed at center with a parallel conductor line (provided that correct installation procedures are followed) balance will be maintained, USING A BALUN, with currents in equal and opposite phase cancelling each other out.
When the connection is to a coaxial cable, WITHOUT A BALUN, this cannot occur because currents flowing inside the cable from the connection to the inner conductor are separated from those flowing on the outside from the connection to the shield, and the result is unbalance causing feeder radiation. However, if the two electrical circuit elements (antenna and coaxial cable) are coupled using a balan, balance will be maintained.
Enter.....The Ugly Balun!.....N4UJW
An Inexpensive, High-Performance, Ugly 50ohm Balun
"Building a no-grief 1.8MHz to 30MHz 50ohm-balun is easy.!"
"No costly ferrite-cores are needed, just a short length of 3 to 5 inch size plastic pipe, about 25 feet of 50ohm coax plus some nylon cable ties.
Solid-dielectric coax is best for this application because foam-dielectric has a tendency to allow a change in the conductor to conductor spacing over a period of time if it is bent into a tight circle. This can eventually result in voltage breakdown of the internal insulation.
The required length of the plastic pipe depends on the diameter and length of the coax used and the diameter of the pipe. For RG-213/U coax, about one foot of 5 inch size pipe is needed for a 1.8MHz to 30MHz balun. For 3.5MHz to 30MHz coverage, about 18 to 20 feet of coax is needed. This length of coax is also adequate for most applications on 1.8MHz.
18 to 21 feet should cover all of 160 through 10 meters.
The number of turns is not critical because the inductance depends more on the length of the wire (coax) than on the number of turns, which will vary depending on the diameter of the plastic pipe that is used. The coax is single-layer close-wound on the plastic pipe.
The first and last turns of the coax are secured to the plastic pipe with nylon cable ties passed through small holes drilled in the plastic pipe.
The coil winding must not be placed against a conductor.
The name of this simple but effective device is a choke-balun.
Some people build choke-baluns, without a plastic coil-form, by scramble-winding the coax into a coil and taping it together.
The problem with scramble-winding is that the first and last turns of the coax may touch each other. This creates two complications. The distributed-capacitance of the balun is increased and the RF-lossy vinyl jacket of the coax is subjected to a high RF-voltage. The single-layer winding on the plastic coil-form construction method solves these problems since it divides the RF-voltage and capacitance evenly across each turn of the balun"....AG6K
Credit for this article goes to AG6K, Rick Measures and was edited from a Pre-copy version of another article titled
"A BALANCED - BALANCED ANTENNA TUNER" published in QST,February,1990
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