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.