Attention, this is a non-political post, for a change :-)
Getting back into ham radio after a decades-long hiatus I need to make a balun for 3-30MHz. Essentially just a glorified common-mode choke and preferably without an extra 3rd magnetizing winding. Realistically I won't use more than 200W but it would be nice if it can take more. There are a bunch of new materials that showed up which I can't remember from the 80's. From some research on the web it seems 61-material is a really good contender when it comes to low core loss yet acceptable permeability. So I was thinking of getting an FT240-61 core. What do thee think?
Main reason I ask is that I remember having blown up a few baluns back in the days and I don't want this thing to cause a meltdown here in bone-dry California.
The EFHW antenna enthusiasts on the Facebook group seem to use type 43 material. Two FT240-43 toroids handle over 100W, and three, up to 1kW (not sure about duty cycles, probably SSB ham chatter). Type 52 is another option, lower loss but lower power handling.
You might find more in this article (which I haven't read in depth):
Looking at the curves for 61 material the losses don't dominate till beyond 50 MHz. 43 material has higher initial permeability but craps out much too early.
That's Micrometals #2 material. Anything requiring power transfer. There are other carbonyl mixes that are better towards 30MHz, but they're special order.
#2 material has worked well for me for _differential_ mode chokes at a couple of MHz, in a differential pi filter, say, the distributed air gap makes it more appropriate than a hard ferrite.
Amidon red is my go-to material for resonant stuff at the lower end of HF and also for voltage-mode baluns. However, it's not very suitable for current-mode.
Fair-Rite made Amidon toroids. Amidon used to print a nice databook that sold for about $15. All I find no w is the datasheet that the always sent with an order. This indicates that #
2 is the only material covering the desired range, but it was created in 20
The Amidon cores are available up to 5.2" OD and a 3.08" ID.
I take it that you and your house survived the fires. Congrats. Same here except the fire came within 1400 feet of my back door.
1:1 Balun or something else like a 4:1 ??
200W CW or PEP? The average power is different. Duty cycle?
How much more power? For how long? Duty cycle?
These might help: (He uses #31 here). Might be more buried on his web pile:
I have four FT240-31 toroids that I was going to use in an HF antenna project which was interrupted by ummm... everything. No, you can't have them. I'm not sure what to recommend for your antenna project.
Looking at the Far-Right data sheets, I would guess(tm) that #31 is better than #61 because of the much higher initial permeability. That translates into needing few turns of wire for the same inductance. Getting a sufficiently large number of wire turns, or more likely coax cable turns, through the toroid hole might be a problem.
It doesn't help that the loss tangent is specified at 100 KHz for #31 and at 10 MHz for #61. Just to make things weird, #31 includes this cryptic statement: This material does not have the dimensional resonance limitations associated with conventional MZn ferrite materials. What's a "dimensional resonance limitation"?
Since power dissipation might be a problem, #61 Curie Temp is >300C, while #31 is >150C. If you're planning on running the balun hot, this might be a consideration making #61 the better material.
Send Jim (K9YC) an email and maybe he can help. Note that he just recently returned from a rather protracted fire evacuation and might be rather busy.
Full disclosure: I bought the four T240-31 toroids from Jim at a discounted price in a group buy through the local radio club.
Hang a galvanized steel bucket under the balun to catch any flaming material selection errors. Or, perhaps consider the possibilities of QRP.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
I guess they mean magneto-striction induced mechanical resonance causing cracking? I once used some small square-loop material toroids where the datasheet said to avoid some frequencies to avoid cracking - these were small cores and the frequencies to avoid were in the low hundreds kHz. Shouldn't be a problem at OPs 3-30MHz.
On a sunny day (Sun, 18 Oct 2020 15:33:15 -0700) it happened Joerg wrote in :
I recently found uk.radio.amateur.moderated may be worth asking there. Still active and no noise!
As to antenna matching, antenna tuners can match any piece of wire... I have a small QRP one... kit from ebay...
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search ebay for "QRP MANUAL DAYS ANTENNA TUNER TUNE DIY KIT 1 - 30 MHZ"
100W would set it on fire. But think if you look for higher power they will have it, else alieexpress:
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:-) why bother with single cores...
Bought some Micrometals Amidon T80-2 Iron Powder Toroidal for experiments long time ago:
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There are a lot of Usenet amateur radio groups:
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the green ones are dead (no longer in active list on nntp.aioe.org), the red one is new, and the blue one is the one I am subscribed to ATM, have not checked the other ones for activity.
For the 10m band I have a GPA, no balun needed, 150 W PEP, Ranger RCI2970DX. Not much used these days. Nothing for lower frequencies than that.
The #2 carbonyl iron material is a nice all-rounder material for just regular inductors in the low MHz range, for inductors that need to store energy. The only bummer is its pretty low Al value.
The #8 material is similar but with a nice boost to the Al value and a little lower transition frequency, it's about 4 times the price though.
Commmon mode chokes don't need to store energy so a hard ferrite is more appropriate, you can have Al values of like a thousand rather than say, 25.
Thanks. On page 12 he talks about his "sheath current lock" or Mantelwellensperre in German (common-mode choke) but not which core he used. It looks fat but small in diameter. Also, he spread te wires a bit far, it's usually better to use a bifilar winding technique.
Thanks. That article would make the 61 material the clear winner at least up to 10MHz. Unfortunately he didn't compare against 31 material. This one has both
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and it makes 61 the winner. Unfortunately at much lower permeability. Of course, at 10MHz 31 is also down to around 150 but that is still more than 125.
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