Re: Toroid material for QRP HF tuner: "2" or "6"?

Shawn Reed

Also...Considering it would be easier to pick up the difference with a resonant ant. at the higher end...I would favor the lower end of rf freq., with some good variables working. There also is the coin to toss. 73,Shawn

On Friday, June 5, 2015 12:09 PM, "mbraner@... [4sqrp]" <4sqrp@...> wrote:

I'm contemplating building a Z-match tuner.  They can be made rather compact if low-voltage capacitors are used (OK for QRP) and the coil is wound on a toroidal core (rather than air-wound).  EMtech sell a nice kit of such a tuner, but I prefer to design and build my own.  There are many designs on the web.  Getting the variable capacitors seems like the hardest (and most expensive) aspect, especially if you want to make the tuner capable of somewhat higher power than strict QRP, say 50 watts.

One thing that I'm puzzled about is the choice of core material for the coil.  It appears that material "2" (as in a "T130-2" toroid, for example) is good for lower frequencies, at least down to 3.5 MHz, but not so good for the high end of the HF range, while material "6" is good for higher frequencies, up to 30 MHz and more, but not so good for 80m.  If you want to build a tuner for the 3.5-30 MHz range, which core is the best compromise?  This may depend on your personal preferences regarding bands used?

Judging by the plurality of designs, "2" is more commonly used, but perhaps the designers were more interested in 80m than 10m?  See for example one early article about a Z-match with toroidal core, by Lloyd Butler - he used a "2", but measured the efficiency, and found it marginal on 10m.

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