New answers tagged balun
1
A balun effectively allows you to connect a balanced antenna (such as a dipole) to an unbalanced feeder (such as coax). You have a balun at the feed point of the antenna, with a coax socket on it, which means that the feeder going from the radio to the antenna is unbalanced.
The HFV-5 is an antenna that presents a 50Ω impedance on its coax socket and it ...
1
Today I made the antenna and included some data, for what it's worth, although this isn't really an answer because the other answers helped me to get to this.
It is a dipole with 33 feet per leg (untrimmed) of insulated #14 stranded wire, with a ceramic insulator and about 10 feet of polyester rope at each end. The height is 10 feet. There are three 8-foot ...
2
How to match a 12.5 ohm balanced antenna to a 50 ohm unbalanced line... I think that has been well answered but one point worth mentioning, and a relevant anecdote...
There are 2 books by Jerry Sevick directly addressing how to do this:
- Sevick's Transmission Line Transformers, Theory and Practice, 5th Edition (2014), by Mack and Sevick
- Understanding, ...
5
Many baluns will work just fine in either direction, though there isn't just one kind of "4:1 balun".
This kind is wound on two cores, and works as a common-mode choke:
simulate this circuit – Schematic created using CircuitLab
A common-mode choke works in either direction, so it matters not which end is balanced and which is unbalanced (or if both ...
2
From personal experience, a good 1:4 balun (50 to 200 Ohm) doesn't necessary work as a good 4:1 balun (50 Ohm to 12.5 Ohm). You can wind just a 4:1 transformer and use it with a 1:1 balun though.
Another simple way to match any impedance is to use an LC-network. There are a lot of online calculators. Personally I particularly like this one. Using this ...
3
Where did you hear that a 40m center-fed dipole λ/4 high has a feedpoint impedance of only 12.5Ω? It will be 75Ω or more. A center-fed λ/2 dipole is only 50Ω at one height.
Here are some graphs. As you can see, you don't need a 4:1 balun.
Ignore the top graph in this first image.
The graph below is based on theoretical values
75Ω coax will be a better ...
4
Depends on how much current you mean by no current.
But in general, unless the dipole is actually perfectly symmetrical, in a perfectly symmetric environment, above a symmetric ground, with the feed line at exactly 90 degrees all the way into the far field, and/or with the radio equipment and their ground connections also exactly 90 degrees perpendicular ...
3
Yes. If the balun is properly designed, there will be little to no common mode current on the outside of the shield.
It is almost always good practice to use an effective choke balun at the feedpoint of any center-fed balanced dipole. The exception would be if some vertical radiation was helpful and the coax was not picking up RFI.
Hotpaw2 makes some ...
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