I'm building my first kit, it's the mcHF SDR radio. Two of the transformers, which relate to the Power/SWR circuit (no further explanation given) use coax on one of the coils (and only one turn at that!). Does the screen in the Coax not stop the transformer from working then?

Interestingly a lot of kit builders are using regular enamelled wire instead of the coax, which they say is too tricky to install, and apparently works fine.

mcHF T2 and T3 transformers

  • $\begingroup$ I'm not familiar with the kit, but I wonder if it's an effort to clean some noise off the ground, (akin to passing it through a ferrite bead) but I'm not sure why you'd want to do that in this application. $\endgroup$
    – David Hoelzer
    Commented Nov 28, 2021 at 21:07
  • 3
    $\begingroup$ This old question and one of the answers show SWR Bridges that have transformers with a single turn made of coax, so it's definitely a thing. One end of the shield is not connected, otherwise you're right, there would be no net current. I can't understand from the circuit diagram, why coax is better than a single wire, except that it's quite flexible for its large diameter. $\endgroup$
    – tomnexus
    Commented Nov 29, 2021 at 0:15
  • 1
    $\begingroup$ Using 1 transformer wind of coax is common in many SWR meter kits. $\endgroup$
    – hotpaw2
    Commented Nov 29, 2021 at 18:53


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