Wire for baluns/Ununs? Any preferences? - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: May 01, 2022, 02:10:03 pm
content: I am looking for better wire for making RF transformers that I hope to use under power someday so they may get hot. I'm going to use teflon wire to prevent shorts from them melting. Any idea where to buy this? Do you have any preferences for buying balun or unun wires?Actually for a long time I've been looking for good sources of wires for use in baluns or ununs for RF. To be housed in watertight boxes and mounted to things like trees.Yes, they are going in my backyard.Why not?

author: Gordo
author_rank: Contributor
timestamp: May 02, 2022, 01:55:37 am
content: Cant help on wire sourcing, but I would advise that trying to perfectly seal an exterior box to house a balun/unun/autotransformer/CMC etc. isn't the best approach. As a guy who has built quite a few of these devices, I would suggest that it has been shown in long ham radio experience that trying to perfectly seal the enclosure does not work well. Even with the best sealing, water always accumulates from condensation, so if your box is to be mounted outside, you need to put some kind of a drain hole at the low point of the box, small is fine. Also be aware that like antenna traps, insects may try to make a home in your box... It's just life...

author: coppercone2
author_rank: Super Contributor
timestamp: May 02, 2022, 02:07:28 am
content: you can put a screen on it, just make a loop of wire, epoxy a screen to it and glue it over a hole. Unless someone decides to pressure wash the tree its gonna be fineI had regular outlets in kinda outdoor locations inappropriately for 14+ years and they work fine (well it got removed by the last electrical work but it was fine, not all the holes were sealed even, the wasps preferred to go somewhere else). Save the money for quality electrical parts IMO, especially in this economy.There was a 15 year old wire nut that was dangling in the wind for thermostat contacts (14 vac) on a solar water heater also, the connection was normal even after all that time, but the wire was stiff enough that it was facing upright. No problems when covered in snow either. The only problem was aesthetics.Sometimes I think that more open is safer from wasps then enclosed because they are scared of predators, but I am not sure

author: profdc9
author_rank: Frequent Contributor
timestamp: May 02, 2022, 03:29:29 am
content: I bought a spool of this from a company that went out of business, and the other day I was looking for more of it and saw it being sold on AliExpress. I'm not sure if its genuine or not. Teflon has good heat resistance so you could test a little bit of it in a well-ventilated area. Burning it could create a little hydrofluoric acid, not very healthy.https://www.aliexpress.com/item/1005003698722537.htmlYou can also use magnet wire in teflon sleeves. Silicone insulation also is also relatively heat resistant and has high dielectric strength, but tends to be thicker.

author: A.Z.
author_rank: Super Contributor
timestamp: May 02, 2022, 08:31:12 am
content: Quote from: cdev on May 01, 2022, 02:10:03 pmA bit of warning here, you shouldn't only care about wire, but also about the Curie temperature of the core you'll use, since if your transformer goes above that temperature you'll literally "cook" the core and it will loose irremediably its characteristics, so be careful to also pick a core size which will allow you to run the desired power w/o overheating the transformer, for QRP a "140" toroid will be ok, willing to go up with power you'll want to go for "240" toroids and eventually stack them one above the otherGetting back to wire, you may also use enameled copper wire of proper diameter, in such a case you'll just wrap your toroid(s) with teflon tape and wind the wire over it (them), for example, if using an FT240-43 as our core and winding a 1:1 current BalUn, a single core transformer will be indicatively ok for a power up to about 500W, willing to get up to 1KW we'll stack two toroid one above the other and wind our transformer, willing to get further up to about 2KW we'll need to stack three toroids; but keep in mind that the max power is also related to the impedance mismatch between the antenna feedpoint and the feedline (the two ends of the transformer), a high mismatch will cause the toroid to heath up more (and dissipate some amount of power to heath)

author: geggi1
author_rank: Frequent Contributor
timestamp: May 03, 2022, 04:25:47 am
content: I use Radox125 from Huber+suner single core cable.The company I'm working for used to do a lot of panel building in the past, but not any more.Over the years I have collected leftovers for many projects.

author: cdev
author_rank: Super Contributor
timestamp: May 03, 2022, 01:06:01 pm
content: Yes, this is my understanding also, and for baluns and ununs I am heading towards te use of ferrite material, not iron powder materials, so I wonder if that makes a difference. and if it does, how much. I have had better results with ferrites. I've also made some ununs and baluns with unknown noise reduction materials.. probably #43 . I dont know. Ive used these cheap cores a fair amount without knowing much about them because I got a bunch of them for very little and it works well.. I make the stuff into dual structures I have been using like one might use a binocular core..Quote from: A.Z. on May 02, 2022, 08:31:12 amIt might be smart to put a temperature sensor in there? Although the possibility of my even having that much power seems remote at this time, I also would like my next antenna to last a while and so could end up in that situation.I dont want ferrites to lose their ability to do their job from heat.Another question I very much have is iron core vs ferrite in an s-match tuner.. To answer this for myself I prety much have to build one.. They are a different kind of transmatch than most people have used before..This is what I am talking about.. They usually use baluns of the iron powder type, usually made of #2 material.. the red enamel coating. I have one of these in my currect slightly funky ATU which is an MFJ differential pi type. Ive been thinking of using it kind of as a transmatch testbed.. changing out a few parts of it.. o see what happens..This is the web page for the "S-match"Its my understanding that as antenna matchboxes go, the s-match is one that acts more like a preselector than most of them. (I like peakiness)https://pa0fri.home.xs4all.nl/ATU/Smatch/smatcheng.htmAnyway, some cofigurations of the S-match peak my curiosiy quite a bit.. I'd like to make some easy to build, small receive only versions of the balanced tuner..

author: cdev
author_rank: Super Contributor
timestamp: May 03, 2022, 01:30:21 pm
content: Quote from: geggi1 on May 03, 2022, 04:25:47 amI'd like to find a gig like that. I hate paying for small lengths of wire, but I am not above scavenging them. I actually used to save enough wire from various junk acquisitions for practically all my needs, its only been recently that Ive had these needs for specialized kinds of wire.SO I think its time to just bite the bullet and buy some bits of what I need.. The 17 AWG size teflon rire looks perfect. Not too big (hopefully) not too small..Previously Ive been using solid insulated Cat6 copper wire in many of my RF/balun/unun projects, also clear speaker wire.. That might actually work really well, I am just concerned that it might get too hot, under some conditions. as I said. (its probably unlikely)But at least now I should be able to become aware of that high SWR situation if it comes up.(now having one of these super useful nanovna2s - also ideal for testing baluns or ununs for loss.. or measuring how well they transform impedances in a broadband way.. thats very important.. I'm aware of how fragile solid state transistors are and whats required to make their premature demise unlikely.. hopefully.Anyway, baluns and ununs pay back effort spent on them fairly well.. for a given amount of work and expense.. They really do.

author: A.Z.
author_rank: Super Contributor
timestamp: May 03, 2022, 02:03:03 pm
content: Quote from: cdev on May 03, 2022, 01:06:01 pmThe "noise reduction" ferrites are usually #31, I just wonder how did you calculate your UnUns/Baluns windings w/o knowing the material type you were using; going by "trial and error" isn't a good way to go, while knowing the material and its characteristics will allow, with a bit of math, to get in the ballpark for a decent windingQuoteThe S-Match isn't bad, but I still prefer the old, reliable L-Match network, ifproperly designedit will offer low losses and will match a wide range of R+X combinations

author: geggi1
author_rank: Frequent Contributor
timestamp: May 03, 2022, 06:08:48 pm
content: Another thing I use for small inductors and transformers/baluns is teflon crossconnection wire used in phone patching panels.Dont know the cross section, but guess something like 0,22mm2.Really nice to work with.Got half a spool from a previous employer.

author: cdev
author_rank: Super Contributor
timestamp: May 03, 2022, 07:27:01 pm
content: Wow, thats a great thing to have..I know what youre talking about, the fine wire.. but boy, I have not seen a phone patching panel since I was staying at the Chelsea Hotel in NYC in the 1970s.Its a residential hotel on 23rd Street in NYC.I have not seen an original PBX or key system since then.. No kidding.. I used to own one, in the same house I'm in today, but, as a kid... I had so much of that stuff.. I havent seen any of those old key systems in while.. Sure could make use of lots of those parts now.. But they are gone.. poof.. Now if you can find hem, (on ebay) they cost an arm and a leg...Its understandable because they were built to last almost forever...(Digium's) Asterisk's takeover has been almost total...That kind of wire is great..Its also sometimes called wire wrap wire... and I still see it. I think its 24 or 26 gauge.. Ive seen this wire fairly frequently and even have some of it.. Here its usually called "bodge wire" and its commonly green.. it denotes an afterward repair wire.. Sometimes its white or blue.. too.. Its very thin and is often silver plated. its pretty useful.Lots of phone system parts are super useful.. Like the yellow tantalum caps they used to have in phones.. Maybe .33 uf? Very useful... Also the 600 ohm matching transformers, they were really quite useful.. Very useful for audio anything.. isolation, etc. Very low distortion.. Two of those would be very helpful with any sound card SDR. For galvanic isolation.

author: cdev
author_rank: Super Contributor
timestamp: May 03, 2022, 08:59:09 pm
content: Thank all of you !for all of your helpful tips! I have had a lot of rewarding times building baluns and ununs, so much that I often dream about it and wake up with antenna ideas.. I dont know why I often find that happening. Its fun, I guess. I always appreciate building things especially if I can so so cheaply!It helps learning new stuff..

author: cdev
author_rank: Super Contributor
timestamp: May 03, 2022, 09:12:05 pm
content: What would you do to suss out what the story is from a number of medium sized blue Arnold toroid cores that I have had for a long time, they seem to be very good inductors.. up to a couple MHz, but not more.. They are marked "A930157-2" Thats basically the story.. very good for low frequencies.. not so much for hiigher ones.. a pretty blue paint on them.. Here we go, that found it.. they are listed as " Molybdenum Permalloy Core"

author: cdev
author_rank: Super Contributor
timestamp: May 04, 2022, 03:05:04 am
content: Quote from: A.Z. on May 03, 2022, 02:03:03 pmzi think weer can make s sort of balanced, small matchbox mini hybrid..A hybrid small balanced hybrid......smatch

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2022, 05:01:42 am
content: Quote from: cdev on May 03, 2022, 09:12:05 pmMPP is exactly what it says: a powder composition with, well, whatever characteristics it has. You can find this number in the catalog, or, unless it's an old number so you need to find an old catalog or the substitutes listing -- I think they changed them at some point.Powdered metals act just like any other metal, in that they have high permeability at low frequencies, up to some cutoff frequency beyond which they drop as 1/sqrt(f) to 1/f (or even faster, if capacitance takes over). Meanwhile on approach to this cutoff point, resistance increases, until it's the equal to dominant component of the core's impedance (i.e., it looks more like a resistor than an inductor).The cutoff depends on material properties, sheet/wire/particle size, and packing density, so it varies from a few 100 kHz for the gnarliest (#26) materials, to some MHz for the better ones (MPP, Sendust, etc.), to 10s or 100s of MHz for the best types (like #2 powdered iron, granted the permeability is so low it's hardly better with the core at all!).Cores aren't automatically useless above cutoff, but you obviously can't run very much power into them before they melt. This is fine for voltage baluns (transformers), where you simply need the impedance many times higher than the line impedance, and you don't much care if that high impedance is absorbing (resistance) or reflecting (inductance) whatever incident power it receives.This generally makes the higher impedance of ferrite preferable to powdered iron, which never have much impedance to begin with (but are cheaper for low frequency power conversion and filtering purposes -- energy storage instead of power transformation).And as ferrites go, #43 for example has a cutoff ca. 10MHz, so it's not too bad in the SW band for instance, despite its most common use as an RF absorber material (ferrite beads, having good resistance in the 30-300MHz range typically). The #61 and #67 ferrites are even higher cutoff (though also lower permeability to start with).Tim

author: cdev
author_rank: Super Contributor
timestamp: May 04, 2022, 11:36:18 pm
content: #61 material works well up into the UHF realm. I use small ferrites with it for UHF baluns..

author: cdev
author_rank: Super Contributor
timestamp: May 05, 2022, 12:44:55 am
content: It depends a lot on their size.. Small toroid cores work better than large ones at higher frequencies..#43 works up into the broadcast FM band.. Small #43 cores... work up to around 100 Mhz. Not much above that, though. And I am sure there is much loss..Quote from: T3sl4co1l on May 04, 2022, 05:01:42 am