Posted: 11/10/2015 8:52:50 PM EDT
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I'm looking to build a matchbox UNUN for an endfed QRP antenna and have a question regarding how to wind the toroid.
How tight and uniform do the turns have to be? Looking online, I've seen turns that are loose, not uniform and/or look haphazard. My thought would be that having the turns tight and uniform would give the best performance. Likewise, securing the wires with epoxy would further maintain the uniformity of the turns. Am I thinking too hard about this? |
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Home brew Earchi. Works as advertised. http://www.pbase.com/david_3/image/161822818/original.jpg Where did you find that case? |
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Where did you find that case? MCM Electronics Type "project box" in their search engine, and you will find about 5000 boxes of different sizes/materials. I can't remember the exact box I used, but I think it was listed under "small (or medium) project boxes". 
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Where did you find that case? Quoted:
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Home brew Earchi. Works as advertised. http://www.pbase.com/david_3/image/161822818/original.jpg Where did you find that case? Radio Shack carries small project boxes too. That is if you still have one local. |
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How tight and uniform do the turns have to be? I like 'em tight and uniform. That's the way I wind toroids, too. 
Altoids tins make pretty good boxes for small projects. This one works well with my IC-703+ and KX3. RANDOM WIRE UNUN FOR MULTIBAND USE WITH BUILT IN AUTOTUNERS 
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Can you buy this somewhere already made? Balun Designs Model 9130 - QRP 9:1 Unun 1.5 - 54 MHz 300 watts |
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Radio Shack carries small project boxes too. That is if you still have one local. Quoted:
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Home brew Earchi. Works as advertised. http://www.pbase.com/david_3/image/161822818/original.jpg Where did you find that case? Radio Shack carries small project boxes too. That is if you still have one local. thats where the box came from in my pic. |
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Can you buy this somewhere already made? Balun Designs Model 9130 - QRP 9:1 Unun 1.5 - 54 MHz 300 watts that power rating is a little -- ummmm, what's the right term here -- "adventurous".
ar-jedi 
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the triple nuts and the cleaned up coax braid approach! i remember that project! 
ar-jedi ps ^^^ pay attention to the details above, kids. see the thin plastic insulators employed both above and below the toroid? this is good practice when using a metal box, because it prevents the UNUN from becoming a dead short when the insulation burns off the windings on the toroid because 100W got injected into the UNUN... |
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the triple nuts and the cleaned up coax braid approach! i remember that project!
ar-jedi ps ^^^ pay attention to the details above, kids. see the thin plastic insulators employed both above and below the toroid? this is good practice when using a metal box, because it prevents the UNUN from becoming a dead short when the insulation burns off the windings on the toroid because 100W got injected into the UNUN... Quoted:
the triple nuts and the cleaned up coax braid approach! i remember that project!
ar-jedi ps ^^^ pay attention to the details above, kids. see the thin plastic insulators employed both above and below the toroid? this is good practice when using a metal box, because it prevents the UNUN from becoming a dead short when the insulation burns off the windings on the toroid because 100W got injected into the UNUN... For something like that, would it make sense to use potting or would that also trap the heat to the point of damage? |