After experimenting with types 43, 52 and 61 ferrite cores, I found which one works the best for 10 meter EFHW's  Type 61 when wound with a full 2:16 turns ratio yields a near perfect match on 20 with 32.5 ft of wire. and acceptable tuning on 10 meters. 1.4:1 vswr.  I am including this pre-cut length of 16 gauge wire with the order. Doubling the wire length (64 ft) gives very acceptable numbers on 40 meters and halving the length will yield equally acceptable numbers on 10 meters, I would equate the versatility of this unun to my Mighty Might unun with the added advantage of being able to handle more power. BNC connector available on request.