Re: Fire In The Wire

Nick WA5BDU
 

Boy, a lot of good info in there Jim. Thanks for taking the time to put it all together.

One point I'll take a bit of an issue with is the suitability (or not) of ferrites such as type 43 for antenna matching transformers.

It's true that the Q can be as low as 1 at HF which can make one wonder how it can possibly be good for anything other than a choke at those frequencies. But it can. My explanation is that most of the losses are core losses caused by the flux in the core. But in a transformer with a high coupling coefficient, flux in the core is minimized and such losses are not excessive.

Your source suggested that with his allowance for transmission line transformers but I think it can be true for conventional transformers and autotransformers as well, although maybe not to the same extent.

Measurements should tell the tale. I did some with FT-114-43 transformers designed for EFHW matching a few years ago  and see losses on the order of 1 dB for 40 through 20. Not negligible but not prohibitive either.

The huge crowd of users of the currently popular homebrew version of the MyAntennas EFHW are using large diameter ferrite cores such as FT-240 to reduce losses as well as handle more power. They've also transitioned from type 43 to type 52 which does lower losses some more. 

Getting back to the original poster - I like the EFHW for field operations because it only needs one support. I'm a total klutz when it comes to getting lines through trees. I also like the Jackite pole (31') as a support.

73,

Nick, WA5BDU

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