diy qrp 1-4 balun - Page 1
Forum section: electronics / rf-microwave

author: p.larner
author_rank: Frequent Contributor
timestamp: November 15, 2023, 06:04:57 pm
content: i have an ft-43 core,its about 29mm o/d and 19mm i/d,its for 3.5-30 mhz,will 11.5 turns be ok,i have 1mm enameled copper wire for the job,can they be twisted together like cat5 then wound on the core?,thanks in advance 73.

author: A.Z.
author_rank: Super Contributor
timestamp: November 15, 2023, 06:30:40 pm
content: no, for a BalUn you will NEED to wind TWO cores, a single core current 4:1 will cause HUGE issues with common mode currents, but then... play it as you want

author: iMo
author_rank: Super Contributor
timestamp: November 15, 2023, 07:23:07 pm
content: Yes, you can use the toroid for a balun.Material 43 is the best one for 3.5-30MHz.The 11 turns is ok.Btw. you cannot have 0.5 turn on a toroid..No need to twist the wires together.

author: A.Z.
author_rank: Super Contributor
timestamp: November 15, 2023, 09:41:50 pm
content: Quote from: A.Z. on November 15, 2023, 06:30:40 pmhttps://www.m0pzt.com/blog/4to1-current-balun/https://www.dj0ip.de/balun-stuff/1-vs-2-core-baluns/again, up to you

author: vk4ffab
author_rank: Frequent Contributor
timestamp: November 15, 2023, 10:33:21 pm
content: Quote from: A.Z. on November 15, 2023, 09:41:50 pmNot entirely true. You are assuming the OP has one of the few use cases where a single core may be problematic. However, the OP has not stated what his use case might be. I use 4:1 transforms all the time anywhere I am chaining RF gain stages together and have never once used 2 cores for the job. I wonder why that is? Because its not a low slung OCF Dipole for 80 and 160m or one of the few instances where it may matter?Rather than being an internet expert quoting yourself and claiming you are right, it might be a good idea to ask the OP what his actual use case is because it really might not matter at all. And even the argument that gets made, parallel inductances are halved on a single core, are still halved with 2 cores, 2 cores will just improve the power rating. Also, even looking at the OP's frequency range, it may potentially be not that great for 80m application dependent, for 40 to 10m its going to be just fine even for an OCF dipole, assuming the core is large enough for the power being put through it.Even in compromised antenna situations, a single core with a hybrid balun winding does the job and assuming the OP has a use case where a single core may be problematic, changing his winding schema can fix that. But, as with many things in ham radio and electronics, the specifics often matter more than some hard and fast rule everyone must abide by.

author: A.Z.
author_rank: Super Contributor
timestamp: November 16, 2023, 03:00:46 pm
content: Quote from: vk4ffab on November 15, 2023, 10:33:21 pmWell, maybe I'm an "internet expert", as you write, I'll have to check that, but ...Quote from: vk4ffab on November 15, 2023, 10:33:21 pmSo, did youmeasurecommon mode currents using a single core and double core 4:1 Guanella on a coax transmission line connected to an antenna ?I did, and didn't like the results.Then, as for the single core and the "hybrid", sure, you may use a single core 4:1 Ruthroff chained to a 1:1 Guanella, that will work, but we'll still be at TWO coresYMMV

author: vk4ffab
author_rank: Frequent Contributor
timestamp: November 16, 2023, 10:40:17 pm
content: Quote from: A.Z. on November 16, 2023, 03:00:46 pmAgain, you are arguing that this matters without giving the specifics of where it actually matters. What antenna and at what frequencies did it actually matter? And is this the implementation that the OP is using? And if you do not know what he is building how can you claim he is wrong?Even the site that you linked in your previous post to claim you are right says the following that you conveniently ignore:QuoteSo which is it? A single core 4:1 is always wrong or is it sometimes wrong based on certain use cases?

author: Andy Chee
author_rank: Super Contributor
timestamp: November 17, 2023, 12:27:00 am
content: Quote from: vk4ffab on November 16, 2023, 10:40:17 pmAs a balun, a single core 4:1 is wrong, simply because a single core is unable to provide sufficient impedance to force balanced currents (the BAL part of BAL-un).But if balanced currents is not a concern, then a single core 4:1 is fine.The OP implies balanced currents in their post (because they mention balun), but balanced currents may not be required in their application (which the OP has yet to elaborate upon).

author: vk4ffab
author_rank: Frequent Contributor
timestamp: November 18, 2023, 01:27:26 am
content: Quote from: Andy Chee on November 17, 2023, 12:27:00 amCan you show the mathematics to prove that statement true?If we say the SRF of the inductance needs to be greater than the frequency of operation and at a minimum the impedance needs to be 10 times the systems impedance for common mode choking. We can work the inductance out of say a Balun Designs 4:1 which is 8T bifilar in parallel with 8T bifilar which is 0.07mH/2 roughly and solve for impedance with Z = 2Pi Freq L. So for an 80m OCF dipole, will a single core provide sufficient impedance for 80m, 40m, 20m and 10m? Without doing all the math for you, this single core 4:1 is not wrong, but it barely doing anything on 80m. On 80m it really needs to be followed with a 1:1 because series inductance add.

author: Andy Chee
author_rank: Super Contributor
timestamp: November 18, 2023, 05:44:07 am
content: Quote from: vk4ffab on November 18, 2023, 01:27:26 amOwen Duffy wrote a comprehensive series of articles with theoretical and practical measurements of the performance of 1:4 single core baluns.https://owenduffy.net/blog/?p=27278https://owenduffy.net/blog/?p=27307https://owenduffy.net/blog/?p=17353https://owenduffy.net/blog/?p=17389There are more balun analyses on his website.For myself, in practice I use a common mode current meter to assess whether the balun is doing a sufficient job.https://owenduffy.net/module/icm/

author: p.larner
author_rank: Frequent Contributor
timestamp: November 18, 2023, 08:14:25 am
content: its for a lashup of a 2x 20m flexweve doublet,one end is on my rafters in the loft,the other leg runs down my roof,its all i can do in the space i have,i used a 1-1 air cored balun but was seeing a z of about 250 ohms wth my vna on most bands,hence why i asked about the 4-1 balun,this is what i cobbled together.

author: A.Z.
author_rank: Super Contributor
timestamp: November 18, 2023, 10:04:52 am
content: oh, this onehttps://vk6ysf.com/balun_4-1.htmwill be ok wound on a #43 (and NOT on a T200-2 !), but you will want to add thishttps://vk6ysf.com/balun_choke_balun_hf.htmbetween the output of the 4:1 and the coax feeder, since the Ruthroff will do nothing to balance currents

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 18, 2023, 08:33:00 pm
content: There's so much... weird information out there in HAM spaces?Well, I might as well chime in some correct information here.What you do get, with two cores, is the ability to choke (note: reduce, NOT eliminate) feedline currents, in event of imbalanced voltage, or impedances.With a series choke, you can go from coax to dipole, direct wired (give or take impedance matching of course, but that's a separate issue), as long as you have somewhere to sink those feedline currents (i.e. ground cable shield to the tower, and preferably at multiple ground points between there and the shack besides).With two cores, you can do the same but doubling the voltage i.e. 1:4 impedance, and still have the choking so it doesn't matter if your feedline is balanced (coax) or not (twisted pair, twin lead). Although this would be a rather odd impedance ratio to use with twin lead let alone ladder line, but again, impedance matching is another matter.Note that "feedline current" is synonymous with affecting the radiation pattern. A dipole for example, subject to CM currents, looks like an extreme "wide" or end-loaded 1/4 wave antenna. Or with tower and/or cable, maybe a end-fed 3/4-wave dipole (i.e. 1/2 wave element grounded at base, driven 1/4 wave on top of it);at suitable frequencies where those models apply.Whether this affects the radiation pattern at any given frequency, is another matter, but in general the pattern (and driven impedance, matching) will be affected by the ratio. So a choke of 500 ohms on a 50 ohm line, expect changes on the order of 10%. Which obviously is a lot if you have watts going to the antenna, no ground return inbetween, and a tenth of that tingling your fingers at the amplifier itself. So ground early and often, or balance precisely, or preferably do both.You can also do it where one transmission line goes straight through for one connection, and in parallel to it, another line choked as a 1:1 inverting autoformer, for the other connection. This is the 1:4 balun in question here. This only needs one core for basic function, and it can use two equal-length TLs (one wrapped on a core to handle the magnetizing flux, other doesn't matter*) to match lengths, extending bandwidth to that limited by the size of connections and symmetry of construction. In other words, turning it from Ruthroff (unmatched delays) to Guanella type.*To the extent CM-DM mode conversion can be ignored. A coax delay line with shield grounded at both ends for example. Twisted pair is less so, and the mismatched impedances to the terminals of that line cause mode conversion, particularly near harmonics of its electrical length. Some choking can be used to improve this, but the full size core of the inverting line is not required.An example looks like this,The blue/black core is the inverting transformer, and the phenolic tube merely supports the delay line. This was a 50MHz amp for which delay matching is wildly unnecessary, but it's easy enough so I felt like being cute and doing it. Schematic here:https://www.seventransistorlabs.com/Images/Wideband_Amp_4W_50MHz_Sch.pngnote they are drawn as common-mode chokes, which, is what they are.In any case, if the antenna-side center-tap is grounded, then the feedpoint will also be common-ground with minimal return current, and can therefore be tied to coax for example without needing two cores, or two full-size ones anyway.Tim

author: vk4ffab
author_rank: Frequent Contributor
timestamp: November 18, 2023, 09:16:40 pm
content: Quote from: T3sl4co1l on November 18, 2023, 08:33:00 pmThat there is,lots of ideology and not a lot of actual knowledge.Quote from: p.larner on November 18, 2023, 08:14:25 amSeeing that your antenna is a doublet, just run the open line feeder all the way back to the radio and use a balanced tuner. That way you remove most of the coax losses due to swr.Quote from: Andy Chee on November 18, 2023, 05:44:07 amApart from Owen and I pretty much agreeing with each other, do you know why he focused on asymmetric loads and 80m?

author: Andy Chee
author_rank: Super Contributor
timestamp: November 19, 2023, 06:37:37 am
content: Quote from: vk4ffab on November 18, 2023, 09:16:40 pmYes. Because:a) real world loads (particularly backyard dipoles) are rarely symmetrical and balanced, andb) several choke implementations on the interweb have inadequate impedance for 80m/160m, causing other issues like ATU flashovers and overheating baluns (also discussed by Duffy).All that being said, the OP’s application is a QRP (~5 watts) doublet, and would probably work ok with a single core 1:4.And your suggestion for direct connection of balanced feeder to balanced ATU would also work, provided the ATU has sufficient matching range.

author: profdc9
author_rank: Frequent Contributor
timestamp: November 19, 2023, 01:03:14 pm
content: A common use of a 4:1 Guanella (current balancing) balun is for feeding an off-center fed dipole. These are multiband antennas that are fed at the 1/3:2/3 ratio point, or sometimes at the 1/5:4/5 ratio point, so that a match is achieved on several harmonic bands simultaneously. This situation tends to be more demanding for a current balun as any common-mode current can heat up the balun if the ferrite material has a lossy permittivity at the working frequency. Sometimes an additional 1:1 current balun, really just a common-mode choke, is also added to reduce the common-mode current further so that this heating is minimized.The single-core 4:1 Guanella "baluns" don't work because both both sets of turns magnetize the same core, and so a zero common current is only achieved for the sum of both of the windings. These windings are in series on the antenna side and are in parallel on the transmitter side. If the two windings have different common-mode currents on the antenna side, only the sum or difference of these currents are choked (depending on the orientation of the two windings on the core) and you still can have residual common-mode current at the transmitter side. I do not know of any useful purpose of this kind of transformer.A 4:1 Ruthroff transformer can be tapped as to provide equal and opposite voltages, as opposed to equal and opposite currents as in a current balun. If you view the two arms of the dipole as separate loads, the current in each arm of the dipole is going to be quite difference if they are balanced in voltage rather than in current. Generally, balancing in current is more desirable, so that the two sides of the dipole are in series rather than in parallel as it would be with a voltage balun, and there is continuity of current at the point where the balun is inserted.

author: A.Z.
author_rank: Super Contributor
timestamp: November 19, 2023, 01:55:00 pm
content: before the guanella "came of age"; hams used voltage baluns and had issues, btw after hams started using coax, unbalanced, feeders; but as I wrote, placing a decent current balun, after a decent voltage one, will offer a pretty good setup for ham radio, all in all we aren't talking about 100KW (or more) transmitters, and then there's the RX side of things

author: LM21
author_rank: Regular Contributor
timestamp: November 19, 2023, 07:24:56 pm
content: I have been experimenting with Guanella 1:4 baluns this autumn.I have made them with two ferrites. I have tried to get high impedance between line ends.Probably best to start with results. nanovna-v2plus4_BalunSWR.png Quite good in my opinion.This was with a twisted line from CAT6 Ethernet cable. Their impedance is 100 ohms. Which is good for a 50 to 200ohms transformer. Picture IMG_20231119_203746.jpgYou didn't tell the power you are using. Coaxial would probably be able to handle more power. There is 93 ohms coaxial cable at Ebay, but I have used only common 50 ohms cable. Those are not so good. IMG_20230815_150718.jpg But the SWR was still below 3 at 30MHz, I think, but I can't test it now because I used ferrites with the twisted line balun. Text is in Finnish, sorry about that. I can't get new photos because I disassembled the balun.I have used EMC ferrites which give high impedance between line ends. I chose Digikey ferrites with high impedance. This is what I usedhttps://www.digikey.fi/en/products/detail/laird-signal-integrity-products/28A0592-0A2/668341I measured SWR with a nanovna-v2plus4, which does not cost too much.I hope all files are there with the post now.

author: p.larner
author_rank: Frequent Contributor
timestamp: November 19, 2023, 10:36:00 pm
content: ok heres another slant on baluns,i have an ugly balun/choke,its 17 turns of 213 on a 5 inch dia former,if i connect the braid to one leg of a doublet and the center core to the other leg of the doublet,then the far end of the coil strait to coax using a pl-259 wll that function as a 1-1 balun?.

author: Andy Chee
author_rank: Super Contributor
timestamp: November 20, 2023, 12:48:33 am
content: Quote from: p.larner on November 19, 2023, 10:36:00 pmProbably not enough impedance for anything below 20m. 10m and up is probably ok. YMMV

author: DonKu
author_rank: Regular Contributor
timestamp: November 20, 2023, 04:33:13 am
content: Quote from: iMo on November 15, 2023, 07:23:07 pmAlthough Type-43 material has lower loss, Type-73 gives the greatest impedance over the HF range.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 20, 2023, 07:03:10 am
content: Note, impedance curves are basically meaningless because they are defined by part geometry. Think of it this way, the index of refraction is approx. sqrt(mu_r). So a wavelength of say 10m becomes some 10s cm in ferrite, and the path length of the core matters.So you get all sorts of shapes, long/tall tubes, short rings, etc., with corresponding different peaks and humps in the impedance curve.It's actually hard to select/design a core for this; ring cores aren't usually rated for impedance, so it's hard to know where to start.Anyway, the HF cutoff is dominated by turn-to-turn capacitance, so the impedance doesn't simply rise forever as turns goes up. Rather, the impedance band shifts lower (and somewhat narrower) with turns. By how much, depends on winding geometry and core materials, though I don't know how much of each, offhand. (EMI CMCs are illustrative, but mostly available in the highest mu / lowest Fc material, so it's hard to gauge how much effect mu/Fc is on overall total.)It's further hard to tell, because the size of core needed for HF work, may not even fully be utilized, i.e. the losses are so strong, field doesn't even get into the middle; at some point it's worth using stacks of short (washer-like) cores, or tubes, instead of thicker parts. Skin effect does not go away, using ferrite, it's just pushed to higher frequencies. IIRC, ballpark figure is power ferrite, mu ~ 2000, resistivity and hysteresis whatever, 100kHz, ballpark 10cm. So, 10MHz should be around 1cm, about the thickness of say a T240.But that's mainly a contraindication of MnZn ferrites (~1 Ωm), so just don't use #77 or #31. NiZn (~1 MΩm) are fine up to higher frequencies. Hysteresis loss isn't that much lower so that's still something to keep in mind (loss is loss, hysteresis still works to cause skin effect), but clearly #43 and #61 do well for middle and high frequencies.I would probably use #43 here, and do some measurements (preferably under power) to determine its impedance. On top of all the grounding and common mode stuff I mentioned earlier, of course.Quote from: DonKu on November 20, 2023, 04:33:13 amAnd, mind, given the above, it's not to say #73 (a MnZn material) is worthless; not saying the above (Amidon) plot is wrong or anything.You can see the above-described effect in the data:https://fair-rite.com/73-material-data-sheet/notice the double-breakpoint response, mu' drops off shallowly around 1MHz, maybe due to hysteresis, then again at 10MHz due to resistivity. Notice the core size, 18/10/6mm toroid. One or both of these breakpoints will depend on core size and aspect ratio, so we can expect lower breakpoint(s) for practical power cores (35mm+ say).Over the 1-10MHz range, the impedance will go something like |Z| ~ sqrt(f), which is useful for ferrite beads where you need losses. That's kind of irrelevant here -- not to say it's good or bad, just that it's beside what we're optimizing for here, which is |Z| over whatever desired HF bands.You see a similar response for #43, but the breakpoint at ~2MHz is steeper this time, and the 2nd breakpoint is much higher (50MHz+?).It may well be that, in thicker sections, #73 retains more |Z| than #43 at this frequency; I suspect it'll be close at least, and I wouldn't feel bad using either in this range I think.Tim

author: A.Z.
author_rank: Super Contributor
timestamp: November 20, 2023, 12:52:28 pm
content: Quote from: p.larner on November 19, 2023, 10:36:00 pmuse the test results from G3TXQ (SK **) as a referencehttp://www.karinya.net/g3txq/chokes/(also seehttps://gm3sek.files.wordpress.com/2019/01/G3TXQ-RC.pdffor further details)air wound chokes/baluns may be ok for single band antennas and then only for low levels of common mode currents, going wideband we'll need to use cores and even then, when it come to choking, willing to cover the whole HF bands we'll probably need two or even three chokes wound using different core materialsas for your doublet, if possible (don't know about your location) try feeding it using as much twin line (ladder or window line) as possible, and put the balun (1:1 don't be fooled by the twin line characteristic impedance) at the end of the twin line trying then to keep the coax run as short as possible**https://gm3sek.com/2019/01/01/steve-hunt-g3txq-in-memoriam/

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 20, 2023, 07:29:58 pm
content: Incidentally, note that twin lead can be choked as well, and bypassed to ground inbetween chokes, making each choke massively more effective. You need to use a balanced DM choke (1:1 CT) to make a midpoint that can be safely grounded, while having little impact on the differential (transmitted) signal. So, several kohms DM impedance to avoid dissipating power and skewing SWR.For coax air core chokes, use this:https://hamwaves.com/inductance/en/index.html#inputenter the dimensions of the shield outer surface. This calculator is accurate including helical waveguide modes, so you can indeed design for the impedance peak (parallel resonance) at the band of interest, and you can see what other bands will be effectively choked down. Note that helical waveguide modes arenotharmonic, because it's a dispersive transmission line.Oh hm, the frequencies will also be lower due to the coax jacket dielectric constant. You'll have to measure it to be sure, but the choke's SRF can be measured with a coupling link, as ye olde grid-dip measurement, assuming you wind it as a self-contained unit without lead length (a choke in a box with connectors will do).Anyway, the important thing to avoid is the series-resonant modes where impedance is minimal. Valley impedance is still higher than Zo so it's not a complete waste, but obviously it's not doing its job at such a frequency and should be adjusted to address this.The use of a core is to increase inductance, greatly reducing the self-resonant frequency while raising impedance (in general, and at resonances), and to dampen resonances by absorbing waves as they travel along the coil. The impedance can therefore remain high (and largely lossy, so, remaining effective while tolerating connected reactances) over a wide range of frequencies, something a plain coil cannot do.Tim

author: A.Z.
author_rank: Super Contributor
timestamp: November 20, 2023, 07:37:14 pm
content: amen to that, Tim !Point is that ... old farts try to convince youngsters to use twin line, but then sometimes, it seems like they forgot about the effects (spectacular sometimes!) of unbalanced balanced lines

author: DonKu
author_rank: Regular Contributor
timestamp: November 20, 2023, 08:28:16 pm
content: Thank you for the Fair-Rite Tech Resources nudge. My Amidon attachment above involved a paper hard copy to digital process. The only available chart uses beads as a base and, on the downside, it demands deduction from readers.Quote from: T3sl4co1l on November 20, 2023, 07:03:10 amLet’s start with permeability. Fair-Rite charts enable an easy side-by-side comparison shown below. (Note the order of magnitude difference on the Y-axis. And the X-axis is also altered with the first and last decades dropped for Type-73 material.) This comparison confirms Type-43 material has lower loss, while Type-73 gives the greatest impedance over the HF range.As an aside, Type-43’s more popular for good reason. Given how apparently Amidon and Fair-Rite stopped manufacturing Type-73 toroids, this topic's moot.

author: iMo
author_rank: Super Contributor
timestamp: November 20, 2023, 08:54:21 pm
content: Quote from: p.larner on November 15, 2023, 06:04:57 pmThe answer for an OP who most probably is a beginner with this great hobby should follow the principle KISS and building up his/her knowledge step by step from simple to complex.A) The 43 toroid is ok for 80-10m band, there is no better material for that rangeB) The size is ok for QRP (it means less than 10W SSB/FT8 usually a beginner messes with)C) 11 turns is ok as the balun's minimum inductive reactance XL seen by the coax should be at least 250ohm at the lowest frequency of interest -> XL (ohm) = 2*Pi*freq*L, where L is aprox 800nH*turns^2 for material 43 of this size (its datasheet AL=800 aprox). This two equations is all they need to know at this stage.D) no need to twist the wire, it is a simple transformer.

author: p.larner
author_rank: Frequent Contributor
timestamp: November 21, 2023, 12:13:02 am
content: twisting the enamelled wires together makes the winding easyer.

author: LM21
author_rank: Regular Contributor
timestamp: November 22, 2023, 02:09:18 pm
content: I see only ferrite charts. What about balun performance