For the 4:1 Ruthroff balun Type 43 or 31 is not ideal for this
purpose, use approx 12 bifilar turns on a FT240-61 core.

Wind the transformer with twin figure of eight speaker cable which is
OK for low power up to about 100w. Use thin 100 ohm twin feeder sold
by Spectrum Communications for higher power levels.

UKM