Skip to main content
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 ...
Phil Frost - W8II's user avatar
17 votes
Accepted

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 ...
Hamsterdave's user avatar
  • 1,844
12 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
10 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
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 ...
webmarc's user avatar
  • 4,234
9 votes
Accepted

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 ...
Marcus Müller's user avatar
8 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
7 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 ...
Phil Frost - W8II's user avatar
7 votes
Accepted

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 ...
Glenn W9IQ's user avatar
  • 18.6k
7 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
7 votes

Why do 9:1 ununs use type 2 material for the core?

I was taught the impedance of the windings at a minimum is 10X the circuit impedance or at least 500 ohms, and greater than 500 is better. That sounds like a good guideline for an isolation ...
hobbs - KC2G's user avatar
  • 12.5k
6 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
6 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
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 – ...
Phil Frost - W8II's user avatar
6 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
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 ...
tomnexus's user avatar
  • 11.4k
5 votes
Accepted

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 ...
Hamsterdave's user avatar
  • 1,844
5 votes

Why isn't twisted pair used for feedlines?

Twisted-pair is just a special case of a balanced (untwisted) feedline. The twisting reduces crosstalk between the multiple pairs in the cable assembly but doesn't otherwise change the fundamental ...
Phil Frost - W8II's user avatar
5 votes

Does a balun need to be made with coax?

Short answer: No, and in fact you'll often get more bang for your buck by avoiding coaxial baluns. The description of the balun's purpose in an antenna system you quote is an oft repeated bit of "...
Hamsterdave's user avatar
  • 1,844
5 votes
Accepted

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, ...
Edwin van Mierlo's user avatar
5 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
5 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
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 ...
Kevin Reid AG6YO's user avatar
  • 24.6k
5 votes
Accepted

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 ...
Phil Frost - W8II's user avatar
5 votes
Accepted

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, mini-...
tomnexus's user avatar
  • 11.4k
5 votes
Accepted

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 ...
hotpaw2's user avatar
  • 13.4k
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 ...
Phil Frost - W8II's user avatar
5 votes
Accepted

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 ...
Chris K8NVH's user avatar
  • 1,042
4 votes
Accepted

what is choking reactance in TLT?

A "Guanella balun" is really just a common-mode choke. simulate this circuit – Schematic created using CircuitLab For differential-mode currents, the current on one half of the transmission ...
Phil Frost - W8II's user avatar
4 votes

Use a TV coax and balun for a poor-man's OCFD?

TV coax typically has foam dielectric and very low loss. On receive it does not matter if you use 50, 60 72 or 75 ohm cable. With short cables, losses are also not important. The cheap TV balun could ...
sm5bsz's user avatar
  • 1,009

Only top scored, non community-wiki answers of a minimum length are eligible