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26 votes

Why do amateur radio operators call an RF choke a balun?

"Balun" is a portmanteau of "balanced" and "unbalanced". Anything made to interconnect a balanced and unbalanced load can be called a balun. A common-mode choke (like a ...
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15 votes
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Why are some 1:1 current baluns twice as complicated as others?

Baluns are a source of much confusion in the hobby, and are probably one of the most common causes of RFI, common mode noise reception, and poor antenna performance. Folks try to shoe-horn a lot of ...
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12 votes
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When would we ever want to use a voltage balun in ham radio?

You'll find voltage baluns in plenty of circuits. For example, the QRP Labs receiver module: HPSDR Pennywhistle (twice, T1 and T3): The Elecraft KX3: A voltage balun can do some things a current ...
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10 votes

What is the capacitors purpose on a balun?

Without having the ability to measure this particular one, I expect that it's to counteract the inductive reactance introduced as a side-effect of the balun design/implementation. Edited to add: check ...
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  • 2,885
8 votes
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Why isn't twisted pair used for feedlines?

Balanced lines (of which twisted pair is a special type) really have an upper frequency limit; you can't use them to transport 1 GHz (well, you can, but the smallest variation in direction or distance ...
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8 votes
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How does a folded balun work?

It's easier to see what's going on with a bit of rearrangement. Imagine this built of tubing: The feedpoint is still where it would be on a dipole without the balun. The feedpoint sees the dipole as ...
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7 votes

Do I need a Balun for a single band QRP antenna?

You don't need a balun, in that it will work and it won't hurt you. But your antenna will not work as well as it ought to. When you are transmitting, the effect of a balun used to connect a coax (...
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  • 23.1k
7 votes
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Does a balun need to be made with coax?

I'll explain the operation of that balun very briefly: for the differential mode (which by definition has equal but opposite currents on each conductor), each conductor induces an equal but opposite ...
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7 votes
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Coax or bifilar windings for a choke?

In most multi-band balun applications, there is rarely a need to maintain a perfect 50 ohm impedance within the balun. The feedpoint or input impedance is varying widely so another impedance bump in ...
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7 votes
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Trying to understand the work of 4:1 coax balun

Think of it first without the feedline: The half-wavelength of transmission line provides a 180 degree phase shift, and the (short) connection between the shield ends is "ground". That means it's at ...
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6 votes
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Where are the baluns for VHF and higher? How can one be made?

Let's clarify some terminology: a balun is any device used to convert between a balanced system (ladder line, dipoles) and an unbalanced one (coax, vertical monopoles). There are a lot of ways to make ...
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6 votes
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How to determine number of turns for a 1:1 balun?

The ideal number of turns depends on core material, geometry, and frequency. This is why you find such variance in how many turns should be used. More turns increases the choking impedance up to a ...
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6 votes
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How does a 1:4 current balun work?

It's a confusing diagram. Some of the voltages are differences between points you might intuitively assume. For example, the $2V$ at the right is the voltage across the entire load (which also ...
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6 votes

How to match low impedance of NVIS Dipole?

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 – ...
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6 votes
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Is this "floating" output single-ended or differential and against GND or VCC?

The other part of me thinks that the DC blocking capacitor will be a low impedance at RF so that the RF is actually "pushing against" GND or VCC but I don't know which one. This appears to ...
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6 votes

How much attenuation (dB) from a balun is expected?

If you do it right, the bead(s) shouldn't get hot at all, and shouldn't add much loss. The impedance of the bead(s) should be about 10 x the impedance of the dipole. The current on the feedline with ...
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  • 8,171
5 votes
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Why aren't there baluns that do BOTH balanced/unbalanced transformation and common mode current attenuation?

There are. I suspect you're confusing a couple of different things when it comes to balance. Common mode current is current which appears to flow on both conductors in the feed line with the same ...
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  • 1,814
5 votes
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How is a 1:1 current balun different from a choke?

Baluns are designed to be transformers (like 1:1 4:1, 6:1, etc.) or choke baluns, and both. For an antenna, the purpose of a choke balun is to create a high-impedance to common mode currents that ...
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5 votes
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Understanding coax radiation and "current on the shield"

Perhaps some of my confusion comes from an audio background, where one has "balanced" and "unbalanced" cabling in a way that is easier for me to understand: an unbalanced cable is simply a signal and ...
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5 votes
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Use a TV coax and balun for a poor-man's OCFD?

OK, let me try to answer this, but this answer may also be qualified as unqualified. If you have a 50 Ohm receiver, and connect a perfectly (Z=R) 75 ohm antenna system, then your VSWR would be 1.5, ...
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5 votes
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Why do we distinguish between balanced and unbalanced?

There are balanced feedlines (twin-lead), and balanced antennas (dipoles), and similar things all described as "balanced". In this sense, balance means the two halves of the thing have equal impedance ...
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5 votes
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Power Amplifier Balun Question

I believe it's a misprint. Comparing the drawing showing the construction of the balun with its schematic representation, it does appear the dot on the lowermost winding (terminals 2 and 5) is ...
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5 votes

Determining Impedance With An Antenna Analyzer

How do I convert the above data to provide the impedance of my antenna, at this point, for this tested frequency? "Z (Ω) = 167.19 - j63.91" is telling you the impedance. The impedance of your antenna ...
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5 votes
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Voltage vs. Current Balun for Dipole

You could rewind it, but the result may not necessarily be better. This is because the core must be optimized for different needs in each balun design. In what you're calling a "current balun", the ...
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5 votes
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UHF cubical quad VNA analysis interpretation

1. You need to re-think your balun. At UHF we don't use toroids and wire, it's always done with transmission lines of varying impedance, on PCB or maybe thin coax. There are transformers for UHF, ...
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5 votes
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Will using a 1:1 balun at the feedpoint of a center feed dipole result in no common mode current on the outside of the coax?

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 ...
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  • 12.5k
5 votes

Actual Impedance of a folded dipole at resonance

Since you say "Terminated Folded Dipole" and mention a resistor, it sounds like you are talking about a T2FD. This is a significantly different antenna from a vanilla folded dipole, which does not ...
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5 votes
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Importance of Ferrite Size in Coax Choke Balun

When making a coax choke balun, does the size of the ferrite matter, and if so, why? Simplest answer: If the choke impedance is low enough to allow some common mode power through, then there is a ...
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  • 1,022
4 votes
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Connect Printed Yagi-Uda Dipole Array with Balun to coaxial cable correctly

I'm no expert on balun designs, but I think they mean to construct a folded balun, as follows. The coax's outer conductor is soldered to the same part of the antenna, but it is left on the coax, not ...
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  • 23.1k
4 votes

How is a 1:1 current balun different from a choke?

A choke is an inductor which is used to block high frequencies while allowing DC to pass. All chokes are inductors (though sometimes more than one inductor), but not all inductors are chokes: to be ...
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