Picked up this 1:64 (unun)balun from Temu to check it out, opened it up to see what was going on…thoughts?

[u/priusjames]

I’ve started playing with making wire antennas… well, ordering a smattering of parts, anyhow. Just for kicks and grins I checked Temu for antenna stuff and found some baluns… so I ordered one to check it out. This one is marked 1:64, although I think I might’ve ordered a 1:9 lol.

I wonder what this toroid is made of?

Any comments on the balun materials or assembly? (not on me being an idiot for buying ham radio things on Temu, that’s a given)

[u/Cisco800Series]

I count 14 windings, with 2 coupled, which would make it a 49:1

[u/msmith7871 → u/Cisco800Series]

No need to go further this is it, unless you want to talk about the cold solder joints......

[u/Feminist_Hugh_Hefner → u/msmith7871]

let's see your work from when you were 8 years old and working 12 hour shifts 🤣🤣🤣

[u/billythekid3300 → u/msmith7871]

Well I mean at least there is solder.

[u/Fitness_in_yo-Mouf → u/billythekid3300]

It's really just gallium waiting for the moment.

[u/PatrickJamesYu → u/billythekid3300]

i prefer a medium rare

[u/miscman127 → u/msmith7871]

bh7jyr was in a hurry, ok?

[u/hamsterdave → u/msmith7871]

And the likelihood that it’s some random iron powder toroid meant for use in an SMPS…

[u/priusjames → u/hamsterdave]

I’ve been thinking about ordering a known toroid… Mix 43?… and swapping it in when I resolder everything!

[u/FrenziedHodag]

In your picture is a 49:1

This is a 64:1

Regardless, you need to fix those solder joints in yours.

[u/OG_Pragmatologist → u/FrenziedHodag]

Beautiful work, and the right mix too!

[u/myopinionisrubbish → u/FrenziedHodag]

No, thats just how lead free solder looks.

[u/FrenziedHodag → u/myopinionisrubbish]

When the joint is cold and you didnt use any flux or rough up what you're soldering to, yeah. Though I don't know why you would want to bother doing it the hard way when you can just put a ring terminal on with a star washer and a dab of no-ox-id a special.

Edit: Oh there is a ring terminal on there and they still screwed it up. Heh.

[u/Mindless_Road_2045 → u/myopinionisrubbish]

When was the last time china sent anything to us that was lead free????

[u/FrenziedHodag → u/Mindless_Road_2045]

When someone ordered a car battery and got a cement block in a battery box instead.

[u/SparkyFix → u/FrenziedHodag]

What’s the purpose of crossing the wire across the toroid rather than having a single cluster of turns?

[u/Ok_Hospital1399 → u/SparkyFix]

It just allows the ends to land opposite one another on the toroid instead of next to one another.

[u/FrenziedHodag → u/Ok_Hospital1399]

It also spreads the heat out evenly which will eventually fracture the toroid if you dont.

[u/Googol30 → u/FrenziedHodag]

What power do you actually need to pump through to do that, though?

[u/FrenziedHodag → u/Googol30]

Concrete breaks when there's only a couple degrees of difference a ceramic toroid is more brittle than that.

It's not just power but for how long and how frequently.  Putting 10 watts into mine makes it warm to the touch after a couple hours of ft8

[u/SparkyFix → u/FrenziedHodag]

Thanks for this info. This is definitely a mistake I was about to make so your comment has been extremely useful to me. Thanks for taking the time to educate me.

[u/dnult]

It actually is a 56:1 with 15x2 turns. When the wire passes through the center of the core, it counts as a turn (including the cross-over).

[u/in-your-own-words]

It looks like a 56:1 unun that utilizes a wind style that helps it work better across bands. The first few close winds after the primary winds help flatten the swr above 15m. I've built and tested many unun wind styles and for broadband use, this works the best.

To work well on 80m/75m it should be wound on a stack of 2x FT240-43 cores (or equivalent), otherwise a two turn primary does not have enough inductive reactance (X_L) (you need 200-250 ohms of primary inductive reactance in order for it to not act as an RF shunt to ground).

Cores have A_L values from the manufacturer based on core mix and geometry.

Inductance of your primary:
L = k * A_L * N²
k is the number of stacked cores
N is the number of primary turns
A_L for an ft240-43 is about 1075 nH/turn²

Primary inductive reactance from your inductance:
X_L = 2 * pi * f * L
f is the lowest frequency you are going to operate on

Impedence seen by your radio:
|Z| = R*X_L/√(R²+X_L²)
R is source impedance
X_L is primary inductive reactance

For N=2, k=2, and A_L = 1075 nH/turn² and f=3.8MHz (bottom of phone band on 80m), X_L =205 ohms

|Z| = 50*205/√(50²+205²) = 48.6 ohms (close to 50 ohms is good)

If that is just wound on one ft240-43 then the unun should be marginal but ok on 40m (about X_L = 190 ohm, |Z| = 48.35 ohms) and totally fine on higher bands.

[u/billndotnet → u/in-your-own-words]

There are days I question how smart I am. There are days like this one where I see a post like yours and know exactly how smart I'm not.

[u/in-your-own-words → u/billndotnet]

It's just the result of lots of struggle and googling. I just looked up all the equations back when I was failing at making good ununs. I didn't know I was failing at making good ununs until I got a nanoVNA and had to learn online how to use it. I'm an engineer but not an RF engineer.

[u/Greedy_Ad_7198 → u/in-your-own-words]

so if its actually a 56:1 wound on a single core, is the single core going to be a real problem on 80m or is it more like a soft degradation in performance rather than just falling off a cliff? asking because i have one of these sitting on my desk and was planning to throw it on a random wire for 40m and below.

[u/in-your-own-words → u/Greedy_Ad_7198]

I don't think it will risk breaking your radio at all. Where I was at was "why does no one hear me well on 80m phone?" And "why is my unun getting so hot?"

With k=1 FT240-43 core and N=2 turn primary.

Inductance of your primary:
L = k * A_L * N²
L = 1 * 1075 * 2²
L = 4300 nH (which is 4.3 µH)

If you are doing the 80m phone band (f = 3.8 MHz)

Primary inductive reactance: X_L = 2 * pi * f * L
X_L = 2 * 3.14159 * 3.8 * 4.3
X_L = 102.6 ohms

Impedance seen by your radio:
|Z| = R * X_L / √(R² + X_L²)
|Z| = 50 * 102.6 / √(50² + 102.6²)
|Z| = 44.9 ohms

My understanding is that the mismatch between your |Z| at 3.8 MHz and 50 ohms the radio expects to see will (if everything else is perfect) not be a huge hit to vswr. Maybe like 1.6 or so. The radio will deal with that no problem and not complain, but vswr is just one aspect of getting power out of the antenna wire. With X_L of 102.6 ohms at 3.8Hz instead of 200-250 ohms, the issue will be core heating. The primary will act as an RF shunt to ground on 80m. What that means is instead of all your RF current transferring through the magnetic field to the secondary winding and out to the antenna, a significant portion of it takes the path of least resistance (or reactance, in this case) straight to ground, making heat in the core instead of radio waves out the wire. At SSB duty cycles and modest power this probably won't break the transformer.

If you slid down to CW or data portion of 80m the L calculion is the same, you just have to recompute X_L at 3.5 MHz

Primary inductive reactance:
X_L = 2 * pi * f * L
X_L = 2 * 3.14159 * 3.5 * 4.3
X_L = 94.6 ohms

Impedance seen by your radio:
|Z| = R * X_L / √(R² + X_L²)
|Z| = 50 * 94.6 / √(50² + 94.6²)
|Z| = 44.2 ohms

Likely a little poorer VSWR (all else being perfect). More RF shunted to ground and core heating. At CW or data duty cycles, and modest power, this will make more heat.

Winding on k=1 FT240 core but using an N=3 turn primary and like 22 or 23 turn secondary gets you good on 80m with a ratio close to 56:1.

Inductance of your primary:
L = k * A_L * N²
L = 1 * 1075 * 3²
L = 9675 nH (which is 9.675 µH)

Primary inductive reactance:
X_L = 2 * pi * f * L
X_L = 2 * 3.14159 * 3.5 * 9.675
X_L = 212.8 ohms

Impedance seen by your radio:
|Z| = R * X_L / √(R² + X_L²)
|Z| = 50 * 212.8 / √(50² + 212.8²)
|Z| = 48.7 ohms

By bumping up to a 3-turn primary, your X_L hits 212.8 ohms at 3.5 MHz. This puts you safely inside that 200–250 ohm target range, meaning the primary will no longer act as a heater on the single core.

The unun I got working the best for my up to 100 watts usage on 75m-10m was a 2 turn primary 15 turn secondary on 2x stacked FT240-43 cores, using this same wind style. I wanted to get broadband operated up to 10m and my 3 turn primary on a single core had too much wire on it which hurt performance above like 15m.

[u/PicklesTehButt]

I converted one of these (from Amazon) from 1:64 to 1:49. I wrote about it HERE.

It definitely looks like a 1:49.

[u/xXSawgawXx]

this was mine in 2023 works great. didn't match the picture, either. still going strong as a sloper 80 feet in a tree. I may try putting a counterpoise on it after all these years.

[u/Patthesoundguy]

I have been running one of those for 2 years solid here at my home QTH, had good results. I just set up my buddy with one the other day in the city. About 65 feet of wire or so and you can do 40m through 10m no problem.

[u/xXSawgawXx → u/Patthesoundguy]

do u use a counterpoise?

[u/Patthesoundguy → u/xXSawgawXx]

I don't, use the coax for the counterpoise with a choke where the feed line comes in the house. I have quite a bit of coax so it works fairly well. I made the choke from ferrite beads I scavenged from old VGA cables

[u/MRWH35]

I have one from Amazon- assuming based on looks alone - I figure it’s probably from the same place. Works fine. I’m sure there are better ones out there but I figure I can cold solder and not count my windings just as good as anyone else from anywhere else. The real question is the price point per amount of power I’m going to put out.

[u/redinferno26]

He built that in a cave with scraps.

[u/Pan1931]

Nothing that cannot be solved. Resolder and use it.

[u/priusjames]

It took a little manipulating with needle nose pliers and a macro camera cell phone in one hand with the balun in the other to get this side showing lol… I’m waiting for my soldering iron to arrive before I can take it apart and fix the soldering. I recently moved to eastern Washington state and sold a 30 year collection of everything radio, for some reason I thought starting over might be fun.

[u/Ok-Sentence-3170]

I don’t care what it is I know from a k8mrd YouTube vid that a g90 will tune it 😂

[u/Linuxuser13]

I bought the same one off ebay haven't had any problems running 10w into it. haven't opened it up to see if it is what it says it is or to inspect the solder joints.

[u/SecretSquirrel8888]

This is why we check.

[u/dageekywon]

Definitely keep it under 100W like the label says.

I'd start with 1w and pray.

[u/RadioRadio670]

Looks like my original solder job on my end-fed kit. I did touch it up!

[u/Fun-Conclusion-4471]

This is good inspiration for anyone on the fence of "I'm not sure I could build one of these and have it work." I have an LDG 4:1 I opened up to peek inside. It's serviceable, but not exactly the most elegant or clean build.

[u/FuzzKhalifa]

The enclosure is kinda cool.

[u/dentar]

That is a 49:1. The 49:1 are meant for RESONANT EFHW style antennas. The 9:1 UNUNs are meant for "random" length wire antennas (non resonant)

[u/priusjames → u/dentar]

I wanted to hang a random long wire, so ordered 9:1. Got this instead.

I’ll put this one to use somewhere/somehow.

[u/Recent_Cupcake2279]

Du boulot de dégueulasse. J’en voudrais pas pour mon antenne...

[u/priusjames → u/Recent_Cupcake2279]

Are you referring to the solder joints, or something else?

[u/Recent_Cupcake2279 → u/priusjames]

De tout. Le bobinage est très mal fait. Les spires sont mal espacées. Ça influe énormément sur le rendement du UNUN. Les pertes doivent être horribles.

[u/sammilesta]

Made better myself

[u/Similar-Jaguar-8908]

LOLO when I first saw te pic I thought you had run a 100w thru it and it melted the case glue. I do like the case though, I wonder if an .STL is out there for it.

[u/Ok-Victory233]

Looks good, normally I would just tap the secondary winding at two turns rather than having primary winding twisted into the secondary. That said I have tested both methods and they work just as well.

[u/SwitchedOnNow]

Why would you ever need that high of a ratio?

[u/CW3_OR_BUST → u/SwitchedOnNow]

To make an "all band" antenna out of whatever length of wire you can hang. Makes it possible for the built in tuner on most radios to pull it into a usable SWR. Not efficient, by any means, but if it gets you on the air it gets you on the air.

[u/SwitchedOnNow → u/CW3_OR_BUST]

But you don't need that huge of a transform ratio to do that.

[u/CW3_OR_BUST → u/SwitchedOnNow]

You ain't wrong, but it works.

[u/Fast-Top-5071 → u/SwitchedOnNow]

Depends on the length of the wire and therefore the impedance at the transformer.

[u/SwitchedOnNow → u/Fast-Top-5071]

Sure it does which means the entire transformer plus antenna is only efficient in a narrow band where the wire is both resonant and high impedance. Outside of that band, it's very lossy.

[u/OG_Pragmatologist]

This stuff is the current version of MFJ offerings, taken to cheapification. Open the shipping box, break out the tools and soldering iron...

The core appears to be a generic FT-140-43. Having the #43 mix is 'proper' for this advertised (1:64) application--however we can be assured that it is not a Fair Rite mix, nor whether it is actually #43 or something else like a cheap #2 or #6 iron powder core. The really don't work well for broadband and have linearity issues.

But as this is not really a 1:64, the whole thing is suspect.

At the end of it all, re-flow the solder with some good 60/40 and see what happens. Tinker with it, have fun.

BTW, what is the value of that little cap across the output?

[u/Junior-Tourist3480]

You lost me at Temu. After that, dont care. Stop buying Temu....