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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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 ...
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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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  • 18.1k
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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What is the maximum number of turns in a ferrite core used as a common mode choke?

The K9YC paper you mention gives data up to 1 GHz on page 49: These data show for these core types the maximum number of turns is just one or two. Furthermore, it's quite difficult to achieve a ...
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6 votes
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Do chokes at the antenna feedpoint stop the coax from receiving signals as well, or just transmitting?

By the principle of reciprocity, if it works for transmit, it works for receive also. Possibly if your receiver and transmitter are separate devices you may end up with a situation where no common-...
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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

What is the maximum number of turns in a ferrite core used as a common mode choke?

The primary issues with coax wound common mode chokes are; The inductive reactance of the choke can cancel out the capacitive reactance associated with the feedline shield thereby worsening the CM ...
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  • 18.1k
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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Choke at feed point of delta loop with Q match

The choke should go at the transition between unbalanced and balanced, which is where the RG-6 meets the ends of the loop wire. You talk of coiling coax: I suggest you coil it around a ferrite core ...
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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
5 votes

Magnetic Loop Antenna with RFI Choke

From my current experience of using Cha F-Loop 2.0: Yes, you most definitely need an RFI choke to use a magnetic loop antenna, and a good one. Magnetic loops are not as good as you might think. ...
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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

Common-mode choke (CMC) hurting my SWR. Live with it? Drop the choke?

A choked end-fed antenna is (or acts just like) a highly off-center fed dipole, where the length of any stub between the common mode choke and the unun/transformer/feedpoint sets the off center ratio ...
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  • 12.5k
4 votes
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Can I use a 1:1 current balun to feed a 1/4λ vertical?

Looking at the pictures of the LDG RBA-1:1, it looks like the answer is yes. It is just a choke that can be used as either a balun or unun. Note that if the vertical has a resonant feedpoint ...
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4 votes

Coax or bifilar windings for a choke?

The advantage of using coax for a 1:1 choke-balun is the constant Z0 of 50 ohms. As can be seen in the following graphs, the only time a 1:1 choke-balun accomplishes a 1:1 transformation is when it ...
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4 votes
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Dipole increased CM current using choke balun

I'm answering my own question after seemingly solving the problem, thanks to the helpful comments I received. Evidently, the ferrite rod core that I salvaged from a Hy-Gain balun was the culprit. I ...
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4 votes

Is this the Correct Ferrite Core to Reduce RFI as a Common Mode Choke?

That does look like a fine core to use, and the photo of your construction looks good. Your coax isn't causing any problems with noise. Try putting the choke at the feedpoint, not at the radio, in ...
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4 votes

Choke at feed point of delta loop with Q match

Forget about air-core chokes. G3TXQ's page that Phil links to in his excellent answer here shows just how much superior ferrite chokes are than air core choke baluns. Please visit k9yc.com and ...
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  • 7,515
4 votes

Do end-fed dipole antennas need choke baluns?

End fed antennas have become quite popular in recent years, primarily due to their convenient installation conditions. Many people subjectively report good results from the antenna. But how the ...
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  • 18.1k
3 votes

Do end-fed dipole antennas need choke baluns?

I cannot speak to the off-center type dipole feeds that use the 1:9 (impedance) transformers, but for the truly end-fed dipoles fed with something like a 1:49 impedance ratio, the answer is, it ...
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  • 590
3 votes
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G5RV Jr. fed with ladder line and coax

That length of 450 ohm ladder line is important. In order to have a reasonable VSWR on the bands that the G5RV was designed for, you should not change it unless you want to cover different bands. The ...
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  • 7,515
3 votes

Is this the Correct Ferrite Core to Reduce RFI as a Common Mode Choke?

The answers here are excellent and I have little to add other than to emphasise / RFI problems are hard / Consider the case of the RFI problem discussed in Electronics Stack Exchange ( https://...
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  • 1,022
3 votes

Importance of Ferrite Size in Coax Choke Balun

I believe the choice of the core size is twofold. As from K8NVH good answer a minimum impedance is needed for the balun to do its job. A common mode impedance much higher than differtial ones ...
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  • 171
2 votes

Magnetic Loop Antenna with RFI Choke

Magnetic loops do not need a choke more than other kinds of antennas but I recommend you have one anyway especially if you will have coax running through your house. The reason to have a choke with a ...
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2 votes

Coax or bifilar windings for a choke?

I strongly recommend "Building and Using Baluns and Ununs" by Jerry Sevick, W2FMI. I have built dozens of coaxial- and bifilar-wound transformers and chokes for use in high-power amplifiers and ...
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  • 7,683
2 votes

When would we ever want to use a voltage balun in ham radio?

I attended a seminar on baluns --as applied to antennas-- at a local hamfest, given by no less a guru than Glenn Shultz, W9IQ. He nicely explained that the only place we need to use a voltage balun in ...
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  • 7,515
2 votes
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There are good guides for building 1:1 current baluns. What about 4:1?

Is it sufficient to construct two 1:1 common mode chokes ... then wire them together as described in the previous paragraph? It is nearly as simple as that. Here's a wiring diagram: In a perfect ...
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  • 7,683
2 votes

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

Different beats have different attenuation at different frequencies. My gut tells me you want at least 6 dB, preferably more. Guys seem to wind their own inductors as RF chokes but not sure how much ...
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  • 373
2 votes

Can I convert an inline 1:1 CMC into a balun feed for a dipole?

I'd say that anything that allows you to securely attach the quarter-wave wires, while being light and strong, is a good way to build your antenna. I'd be leery of attaching the wires to banana plugs ...
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