An opinion on balun design - 4:1
I am in the process of putting up a wire antenna that requires a 4:1 balun. having done the research I have been looking for 4:1 current balun designs.
I have noticed that there are various designs about, and I intend to home brew the entire system. My intended manual antenna tuner does not have a balun in it.
While reading one of many web sites on the subject the other night I saw a comment along the lines of ' a proper 4:1 current balun cannot be made from a single core' - yet I have seen many designs that appear (or purport) to be 4:1 current baluns, wound on a single core. Many others are dual core.
This is what I intend to build, it is dual core
Am I on the right track??
I'm also experimenting with various balun designs, and found that there are two "camps" of balun designers, each of them has different approach for balun design:
1. Balun is not a transformer, just ferrite is used to stop stray currents, so it's permeability, size, does not matters at all, just all wires should not intersect and be transmission lines, not transformer windings.
2. Balun is wideband transformer, where's cross-winding and ferrite core is used to achieve wide working band. These guys pay big attention to the ferrite core and also reccomend to wind it using crossed wires.
So far, I've went trough #1 ways and quickly discovered that, #2 guys are correct, when selecting material for the core. For example, material with 2000 permeability worked fine in 1-10mhz range, but material with 600 permeability worked fine in 14-28mhz range.
Later, I will try to wind balun using intersected wires, and will report, how it works.
Here is the design of the balun Goeroe himself
Originally Posted by ZL2ARL
And yes, on 2 Cores .....
I also plan a home made 4 to 1 balun. Unless someone comes up with a better thought I was going to use this idea from Roy LeWallen he said it was a "superior" design.
Pradon my ugly recreation but I think it shows enough to convey the idea and how to construct.
My problem now is selection of cores: I have access to almost any style of Amidon core but am slightly confused by an abundance of options. Any suggestions?
Yes, you are on the right track. What I read on your link looks OK except for very minor points.
The crossover winding really does NOTHING electrically. It does not hurt, it does not help.
A single core balun can only be a 4:1 VOLTAGE balun. It can never ever be 4:1 CURRENT BALUN ON ONE CORE. If you try to make a 4:1 current balun on one core it will horribly unbalance the antenna system.
The 4:1 design on this link:
Originally Posted by PD7MAA
is terrible. It will unbalance any system.
I hope to make a 4:1 current balun by winding RG303 coaxial cable around a pair of T300-2 cores. Input side has the cables in parallel, output has them in series. Any thoughts about using coaxial cable instead of parallel wires for this application? I see coax used in BalunDesigns 1:1 current balun, but not in the 4:1 current balun.
It depends on the application!
Originally Posted by VO1KS
I have wound 1:4 current baluns with coax where it was important to achieve a particular characteristic impedance. In my application I had an antenna with a feedpoint impedance of 12.5Ω which I was matching to 50Ω; that required the characteristic impedance of the windings to be 25Ω, which I achieved with parallel 50Ω coax pairs.
In many other applications - particularly when a wide range of differential load impedances will be experienced and the Zo of the winding is not important - it may be better to use a bifilar pair insulated with Teflon sleeving to provide a higher breakdown-voltage capability than you could achieve with coax.
The only time I can see you would want to wind a 4:1 with 50Ω coax is if you were matching between 100Ω and 25Ω.
Finally, just to re-inforce Tom's comment: you cannot build a 4:1 balun comprising two 1:1 chokes on a common magnetic circuit. Through transformer action, the common magnetic circuit must drive the CM voltages across the two chokes to be identical. On some load configurations that will guarantee current imbalance.
Originally Posted by W8JI
This looks to be almost the same as the design I intended to use, can you explain why it is so terrible?
The 4:1 balun at that link shows two transmission line transformers on one single core.
Originally Posted by ZL2ARL
That forces the 4:1 section of the balun to be an unbalanced voltage source.
An unbalanced voltage source tries to force any load into unbalanced operation.
Any current balun of 4:1 ratio has to use two independent magnetic paths, which means two isolated cores or stacks of cores, for the two transmission lines.