Baluns, Chokes, Isolators, UnUns and Ferrite Toroids for HF+VHF. We offer the best prices for FT140-43, FT140-61, FT240-31 and FT240-43 toroids in the UK - perfect for your balun projects. The following chart shows how different ferrite materials perform across HF. The green band indicates "resistive", which is desired for best performance. In most cases, 8 turns on an FT240-31 (of RG58 or RG142 depending upon power requirements) will suffice. 12 turns is better for a <15MHz aerial setup.