The following diagrams and tables show some simple 1:1 and 4:1 baluns for use between 1.8 and 30 MHz using twin transmission lines made from enamelled copper wire (ecw). The bifilar windings have been adjusted (spacing) to produce transmission lines with Zo of 50 or 75 ohms as required for best matching. These designs should be suitable for 100-200 Watt operation.
RF transformers should always operate within safe limits of temperature and linearity. The following designs which use toroid cores can be checked for safe operating conditions with the programs included in Programs.
- Ferrite Core: Select either rod or toroid core as detailed below
- Core insulation: 1 layer of ptfe tape (plumbers thread sealing tape); plumbing and hardware suppliers
- Wire: 1.0 or 1.25mm enamelled copper wire (ecw) as specified; electronics shops
- Spacing material: Kinnears 540 TEX colourfil twine; product code K 069048; newsagents, craft suppliers
- Note: This spacing material is polypropylene; other material is probably suitable, but ensure it will not absorb moisture.