Questions tagged [balun]

Devices for connecting balanced and unbalanced feed lines/antennas. Also covers questions about ununs, unbalanced-to-unbalanced connection.

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RFID extension cable

I am trying to build an extension cable to relay an RFID signal (125kHz) to various distances (2,5,10m). I am using 2 identical antennas at the two ends of a 75Ohm coax cable, and I also put 2 ...
3 votes
1 answer
92 views

Using PVC coated solid-core wire for a small number of turns on toroid

I'm researching making my own 49:1 unun using an appropriate mix ferrite toroid and some reasonable gauge solid-core wire. (This is for an experimental HF end-fed antenna, though this detail probably ...
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2 votes
4 answers
207 views

Is an off-center fed dipole (and/or doublet) inherently unbalanced?

Does a balun/choke have to "work harder" in an off-center fed dipole than when the feedpoint is at the center? Or do the standing waves that develop keep the antenna balanced electrically ...
1 vote
1 answer
126 views

RG-174 vs RG58 for winding toroid

I'm building a balun for a fan dipole, and this chart suggests 9 turns of RG-58 on two FT240-31 cores will give good performance over the frequency range of interest. However, I don't feel confident ...
3 votes
1 answer
74 views

Ferrite choice for fan dipole

I am intending to build a two element fan dipole for 80 and 20m. How should I go about choosing a ferrite toroid and number of windings for the balun, to operate effectively over such a range of ...
2 votes
2 answers
410 views

End fed long wire antenna causing issues

I use a hex beam to operate from 20 meters to 6 meters with amazing results. I wish to operate 40 meters and 80 meters also, and can only really install an end fed long wire due to my installation ...
0 votes
1 answer
91 views

How to Feed 2 x Co-Phased 4 Element Yagi Antennas?

I am wanting to build 2 x 4 element vertical yagi antennas for 28 MHz and co-phase them and feed with one 50 ohm coaxial transmission line. If i were to use a gamma match for each yagi and tune them ...
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0 votes
1 answer
539 views

End fed long wire antenna for 40 meters length

I have a hex beam antenna that gets me onto bands from 20 meters to 6 meters very well. I wish to have an antenna that gets me onto 40 meters at night very well also. Recently I purchased an end fed ...
3 votes
4 answers
451 views

Issues with high SWR on HF Kits EFHW 49:1 UnUn kit

I recently tried assembling a EFHW kit, and some problems came up in testing. I believe this is the kit; I bought it through ARRL: HF Kits website. This is my first time making an UnUn and EFHW kit. ...
1 vote
2 answers
168 views

How do I configure a NanoVNA v2Plus4 to check a 1:1 Balun?

Note that the menus are different than those I'm seeing on YouTube which aren't for the V2plus4. What's missing is "Isolation" and of course, there is an additional standard for that which ...
3 votes
2 answers
92 views

VHF Balancing, necessary? Methods?

This is a question about power dissipated due to radiation and ohmic heating caused by common mode current in the coaxial shielding, specifically at VHF frequencies. When a balanced antenna (such as a ...
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2 votes
3 answers
132 views

Ferrite unun transformer to match antenna resistance loads of <50Ω?

For LF/MF (2200m/630m), I am interested in the situation of a vertical antenna with capacitance hat top-loading, where the vertical antenna is VERY short compared to wavelength, and the antenna is ...
6 votes
2 answers
232 views

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

I'm building a dipole antenna for 433 MHz, first one ever. I will have to use a ferrite bead to balance the feed. How many decibels of attenuation should I expect from the ferrite bead?
6 votes
3 answers
2k views

When is a balun a Guanella?

I've searched this site, wikipedia, other sites, and haven't found a clear answer: What features or parameters of a balun or choke put it into the category/definition of a "Guanella"? Where ...
-2 votes
2 answers
300 views

Can an end-fed be fed with an Isolation transformer? [closed]

Typical half-wave end-fed antenna kits include either a 9:1 or 49:1 toroidal balun or unun, which is a transformer for impedance matching, but with one primary winding endpoint (for the coax shield) ...
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2 votes
2 answers
202 views

Can I wind my 9:1 unun with two wires instead of three?

All the 9:1 unun tutorials out there are using three wires to wind, but I was wondering if it is possible to wind it using two wires similar to how this 49:1 is built (https://elginradio.files....
0 votes
2 answers
135 views

At near-QRP levels should I include a balun/unun in the antenna system? [duplicate]

To my comprehension a BALUN/UNUN is an RF Transformer. If this is correct and since a BALUN/UNUN is part of the antenna system ... how much power does one expect to lose there? Specifically, how much ...
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3 votes
2 answers
175 views

1:4 Guanella unun current balun

I am having trouble understanding the 1:4 Guanella current balun here. So at DC, or low frequencies, I think the current path would be a short to ground. At higher frequencies, I am getting confused ...
1 vote
1 answer
222 views

There are good guides for building 1:1 current baluns. What about 4:1?

Some dedicated hams have spent a lot of effort gathering empirical data on various constructions for common-mode chokes. For example, G3TXQ's work is commonly referenced, and K9YC's is pretty well-...
4 votes
1 answer
539 views

Debugging SM0VPO's spiral loop antenna build

I had built SM0VPO's spiral loop antenna. And here it is. Recently I got myself a NanoVNA to see how finnicky it is to be tuned with that poor man's tuning cap. I brought it from 12 MHz into the 14 ...
3 votes
1 answer
122 views

Is this "floating" output single-ended or differential and against GND or VCC?

I'm looking at a simple FM transmitter output (see picture). It is from the collector of a transistor and it goes through a DC blocking capacitor before the antenna would be connected. The entire ...
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4 answers
198 views

Weatherproofing coax connection to balun

How should a coax-to-housing connection like this be weatherproofed? It doesn't seem like taping is going to do much good here
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4 votes
3 answers
1k views

What is the capacitors purpose on a balun?

Per the subject, what is the capacitors purpose on a balun? Used a lot on wire wound ferrite toroidal baluns.
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4 votes
2 answers
354 views

Heat-shrink as dielectric for bazooka balun?

I'm intending to make a sleeve balun (aka bazooka) for 2m, but rather than keep the lossy coax jacket as a dielectric (I have some RG58), was considering to remove it and replace it with heat shrink ...
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0 votes
1 answer
339 views

Pondering variations on the vertical bazooka antenna

I've seen these antennas built out of coax that are called a bazooka vertical. It's a kind of 1/4 wave vertical, or perhaps a 1/2 wave dipole. Constructing such an antenna is to roll back the outer ...
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5 votes
2 answers
811 views

How does this quarter-wave stub balun work?

I was searching for 1:1 balun designs that would be efficient at VHF yet could easily be made from commonly available materials when I came across these two: While the design on the right seems ...
9 votes
2 answers
4k views

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

In a world where common mode current is the enemy, and we're constantly doing what we can to avoid RF in the shack, why would we ever choose a voltage type balun over a current balun? I understand ...
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9 votes
2 answers
1k views

Importance of Ferrite Size in Coax Choke Balun

The question is quite simple: When making a coax choke balun, does the size of the ferrite matter, and if so, why? I have seen design notes that say to use a single FT240-43 toroid for powers up to ...
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2 votes
2 answers
1k views

Is a balun really necessary for a small loop antenna?

I am in the process of designing a small receiving loop antenna for the lower HF bands. By small I mean a circumference of less than $0.2\lambda$. Thus, a uniform current distribution can rightly be ...
0 votes
2 answers
425 views

2 meter coax cable balun dimensions for use with a ground plane?

I have a commercially manufactured ground plane antenna for 2 meters. It will be fed with about 150 feet of RG 8/U . I've seen pictures of a coil of the feed line going to a 2 meter ground plane; this ...
3 votes
0 answers
609 views

9:1 unun material and power loss

I need to build another 9:1 unun and I start searching for my toroids... (I have build 2-3 something like 4 years ago)... In parallel I checked on Google about the correct toroid etc so I found 2-3 ...
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5 votes
2 answers
172 views

4:1 Balun question

With an OCF dipole, does it matter which leg, short or long, is connected to which side of the 4:1 balun, hot(coax center) or shield? How can you tell which is which, the balun is not marked. Thank ...
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5 votes
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What causes differences in properties of ferrite cores from same material?

Why are the shapes of the impedance curves different for cores made of the same ferrite material? The impedance (Z) of an inductor wound on a ferrimagnetic core is: $$Z=j\omega L_s + R_s = j\omega ...
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2 votes
1 answer
158 views

What is the delay through a 1:4 Guanella balun?

I need to estimate the signal delay through the 1:4 Guanella balun shown here: Is the delay simply the delay through the winding on CORE1 or CORE2? For example, assume each winding comprises 0.1-m ...
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19 votes
3 answers
3k views

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

When using a balanced antenna such as a half wave dipole, with an unbalanced feed line such as coax, an RF choke can be used to block RF current emitted by the transmitter from splitting up at the ...
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1 vote
3 answers
283 views

Can I build a guanella balun using single strand wire instead of coax?

I am trying to homebrew a cobweb antenna and need some help understanding the guanella balun used as described here: http://www.karinya.net/g3txq/cobweb/ This author used RG316 coax around the ...
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4 votes
2 answers
473 views

Actual Impedance of a folded dipole at resonance

I am using a Folded Dipole which I bought when I first got my General License. It was advertised as an all band antenna. My results with it were less than the claims made by the makers to say the ...
3 votes
1 answer
1k views

Trying to understand the work of 4:1 coax balun

Let's consider the following picture (source): When current passes the half-wavelength matching section it changes the phase to the opposite, this is why we get +V and -V in the feed point, 2V ...
4 votes
2 answers
938 views

Does a dipole require a 1.5:1 balun?

Dipoles ideally have 72 ohms impedance. I know most of the time this isn't what one gets and it can vary a lot. But let's assume we can build this perfect dipole that exhibits this impedance. Why do ...
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2 votes
1 answer
1k views

300 ohm to 50 Balun at antenna feedpoint, or near receiver?

If I build a folded dipole, it will have an impedance close to 300 ohms. I have to match this impedance to the 50 ohms of my transceiver. I know many people match that impedance with varying lengths ...
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0 votes
0 answers
36 views

UHF cubical quad VNA analysis interpretation (part2)

This is the follow up to: UHF cubical quad VNA analysis interpretation This is a S21 and S31 analysis of an oversized 385 Mhz 50 Ohm to 90 Ohm balun between 100 Mhz and 600 Mhz I tested phase ...
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1 vote
1 answer
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Rotatable Dipole & RF Choke

I have a Diamond HFV-5 (rotatable dipole) in the attic fed by ~30ft of coax. The antenna system comes with a Balun at the feedpoint. Would it be worthwhile to add an inline RF Choke (Unun) in addition ...
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5 votes
7 answers
1k views

How to match low impedance of NVIS Dipole?

I want to match a 50-ohm coax feed wire to a 40-meter NVIS half-wave dipole. NVIS antenna examples I've found are usually based on a regular dipole (72 ohms in free air). However the impedance drops ...
2 votes
2 answers
286 views

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?

Will using a 1:1 balun at the feedpoint of a center-fed dipole when using coax result in no common mode current on the outside of the coax ?
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3 votes
1 answer
237 views

UHF cubical quad VNA analysis interpretation

I've designed a two element UHF cubical quad. It was designed to resonate at 385 Mhz. I used 0.1mm thick and 1cm wide copper tape instead of wire to lower the antenna Q. I used PVC electrical conduit ...
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4 votes
2 answers
328 views

Dipole increased CM current using choke balun

My 20 meter inverted vee dipole is fed with 56 feet of 50-ohm coax. The SWR measures 1.2 at the center of the band. According to http://arrl.org/grounding a balanced antenna doesn't need a ground, so ...
3 votes
1 answer
632 views

How does a 1:4 current balun work?

I'm having little difficulties understanding the following schematic: I understand the part regarding current distribution. I understand why this schematic suppresses common mode current. Also I ...
1 vote
3 answers
5k views

How to calculate impedance in antenna design's practice?

I would like to make a match half wave length (λ) dipole antenna (or probably a short dipole antenna). So I would like to make it by measure using LCR meter. What I am still confuse is about what is ...
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2 votes
4 answers
5k views

Voltage vs. Current Balun for Dipole

I'm a new radio amateur setting up a half-wave 10-meter inverted vee antenna fed by 50 ohm coax. I understand that the inverted vee lowers the normal 72 ohm dipole closer to 50 ohms, so I only need to ...
1 vote
0 answers
76 views

advice needed for balanced line terminals

I am designing a portable antenna with a radiating element and a balun that are not close to each other. The impedance has been designed to be close to 50 ohms. ...
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