2m 4 element, another interesting issue

[mr_fx]

ok so my 4 element 2m quad is working great, BUT I noticed when we had it on an analyzer that if you touch the coax the SWR changes, if you mast it changes, if you move the coax it changes...

so I am thinking either a balun or an RF choke... not sure which would be most useful in this case

 

[KC9Q]

You need a 1:1 Current Balun or an RF choke. They're one in the same.

If you use coax to build a choke, do not use cable with foam dielectric. Use one with polyurethane or Teflon to prevent the center conductor from migrating to the shield and shorting out. It won't happen immediately, but it may take several months to happen.

73,
Mike

 

[wavrider]

As mentioned in your other thread.

I am a firm believer in chokes or baluns at the feed point of the antenna.

Wrap and RF choke/ugly balun and check the results.

 

[W5LZ]

KC9Q,
I can't agree with your post for a couple of reasons. The first is that, "You need a 1:1 Current Balun or an RF choke. They're one in the same.". A balun and an RF choke are not the same at all, they do two different things. The purpose of a balun is to change from a balanced to an unbalanced state. An RF choke can't do that at all. They both do have a characteristic of reducing CMCs, but that's not the same as balanced to unbalanced. You might wind up with the same results using either, but the 'route' in getting there is different.
Chokes made from coax with foam dielectric insulation are also certainly possible. It does mean that there may be different diameters when winding those chokes though. The same thing applies when using coax cable of different 'sizes' or methods of construction, how it's made. That 'migration' is a possibility with any coax cable, admittedly more of a problem with cable using 'softer' dielectric insulation though.
- 'Doc

 

[KC9Q]

Doc,

There are two ways to make a 1:1 choke or balun using either two parallel wires or coaxial cable. When making a Guanella (Current) balun you have either the parallel wires or coax wrapped around a ferrite rod or a ferrite core. This winding(s) requires tight bends that would destroy foam dielectric coax. They are actually the same thing electrically, just that one is wound with two wires in parallel, the other with one coaxial line. The "Ugly" balun is a Guanella current balun wound either on a feritte core or an air core. Thus, by definition and by construction, all Guanella Current baluns are choke baluns no matter what their ratios are.

The Maxwell balun is a current balun made by placing multiple ferrite cores over coaxial cable. In that case one could use foam cable, however the other two methods usually produce a more heathier choke in a smaller space.

The only time when a 1:1 balun is not equal is if one is a Guanella (current) and the other is a Ruthroff (voltage) balun. The Guanella balun provides choking, as it seeks to provide balanced current to the load (antenna), whereas the Ruthroff (voltage/transformer) balun provides equal voltage to the load (antenna).

The Ruthroff balun is fine for a symetrical antenna like a dipole or a yagi. The Guanella is useful for any antenna configuation, as it does not need a sysmetrical load to function properly. This is why a current balun is considered the proper balun for an OCF antenna.

73,
Mike

 

[hookedon6]

there are RF chokes,..... inductorsdesigned to reduce AC hum or ripples in a dc power supply

there are baluns, a device used to match impedance differences


they are 2 seperate and different components

an RF CHOKE made of coils of cable is NOT a balun

 

[KC9Q]

Then how do you make a 1:1 balun?

 

[Captain Kilowatt]

Then how do you make a 1:1 balun?

One way is to use a trifilar winding. (three wires)

 

[KC9Q]

Here's pictures of proper current baluns: one using parallel wire, and the other using coax. Both are designed for 50 ohms.

The three wire Turrin balun shown above is a voltage balun that has no choking capability.

 

[W5LZ]

Define 'balun'.
Define 'choke'.
Show me where balun = choke. They do different things.
- 'Doc

 

[KC9Q]

Hi Doc,

Get the book "Building and Using Baluns and Ununs" by Jerry Sevick, W2FMI. Section 1.3 describes the choking capabilities of a Guanella "choke" balun.

In it, it states: "Several important points should be made regarding Guanella's 1:1 balun shown in Figure 1-2A. With sufficient choking reactance, the output is isolated from the input and only flux-cancelling transmission line currents are allowed to flow. With matched or very short transmission lines, the grounding of terminal 5 (actually or virtually like the center of a dipole) results in terminal 4 becoming +V1/2 and terminal 2 becoming -V1/2 -- creating a balanced output. This type of of balun has lately been called a 'current' or 'choke' balun."

Thus, the "ugly" choke balun is a form of the Guanella current balun. And if all Guanella baluns are choke baluns, then it is true that the 1:1 Guanella balun is equal and the same as a choke balun. Thus a 1:1 current balun ='s a choke balun. In fact, any form of a Guanella current balun is by default a choke balun, be it 1:1, 2:1, 1:2, 4:1, 1:4, 6:1, 9:1, etc.

73,
Mike

 

[hookedon6]

... the choking capabilities of a Guanella "choke" balun.

... This type of of balun has lately been called a 'current' or 'choke' balun."
Mike

thats the point,... why do you put " around the word balun? how does a 1:1 "balun" change the impedance?. a balun (BALanced to UNbalanced) by defination is an impedance matching device.


a "choke balun" is a misnomer because it doesn't actually balance the line, but does provides isolation for the transmission line. The proper name for such a device is an RF CHOKE. thats most of the confusion,.......... if the incorrect term is used often enough, then after a while some people don't know it is incorrect.

 

[W5LZ]

Sorry Mike, that's an invalid argument. Sevick implies that himself with, "This type of of balun has lately been called a 'current' or 'choke' balun.". You can call your cat 'Fido' but that doesn't make your cat a dog. It only means you've given you cat a dog's name.
Choking off CMCs doesn't define a balun. That is only an incidental property of a balun. It's purpose is to change a balanced state to an unbalanced state. Impedance transformation is also not the purpose of a balun, although it's certainly possible for a balun to do that transforming by it's construction. All baluns do that balanced to unbalanced thingy, not all of them change impedance. By the same token, chokes reduce/stop CMCs from flowing, but all of them don't do the balanced to unbalanced thingy.
The names of both of them, balun and choke, describe their intended purposes by their names. They 'share' certain properties/abilities, but that doesn't mean that they are the same thing at all. It's just an example of being misnamed.
- 'Doc

 

[KC9Q]

Doc,

What you are then saying is the device that connects a 50 ohm balanced dipole to 50 ohm unbalanced coax is not a balun (Balanced to Unbalanced) ,but just a choke?

 

[W5LZ]

No, that isn't what I'm saying at all.
- 'Doc