diy qrp 1-4 balun

[DonKu]

Thank you for the Fair-Rite Tech Resources nudge. My Amidon attachment above involved a paper hard copy to digital process. The only available chart uses beads as a base and, on the downside, it demands deduction from readers.

It's actually hard to select/design a core for this; ring cores aren't usually rated for impedance, so it's hard to know where to start.

Let’s start with permeability. Fair-Rite charts enable an easy side-by-side comparison shown below. (Note the order of magnitude difference on the Y-axis. And the X-axis is also altered with the first and last decades dropped for Type-73 material.) This comparison confirms Type-43 material has lower loss, while Type-73 gives the greatest impedance over the HF range.

As an aside, Type-43’s more popular for good reason. Given how apparently Amidon and Fair-Rite stopped manufacturing Type-73 toroids, this topic's moot.

[iMo]

i have an ft-43 core,its about 29mm o/d and 19mm i/d,its for 3.5-30 mhz,will 11.5 turns be ok,i have 1mm enameled copper wire for the job,can they be twisted together like cat5 then wound on the core?,thanks in advance 73.

The answer for an OP who most probably is a beginner with this great hobby should follow the principle KISS and building up his/her knowledge step by step from simple to complex.

A) The 43 toroid is ok for 80-10m band, there is no better material for that range
B) The size is ok for QRP (it means less than 10W SSB/FT8 usually a beginner messes with)
C) 11 turns is ok as the balun's minimum inductive reactance XL seen by the coax should be at least 250ohm at the lowest frequency of interest -> XL (ohm) = 2*Pi*freq*L, where L is aprox 800nH*turns^2 for material 43 of this size (its datasheet AL=800 aprox). This two equations is all they need to know at this stage.
D) no need to twist the wire, it is a simple transformer.

[p.larner]

twisting the enamelled wires together makes the winding easyer.

[LM21]

I see only ferrite charts. What about balun performance