here are values for CW portions of the USA The 49:1 unun with 3000 ohms of resistance shows a VSWR under 10:1 from 160M to 15M, and less than 3:1 from 80M to 20M. <> an auto-tuner at the base vs. the same antenna fed a 4:1 balun wound with 75 ohm coax on two separate type 43 ferrite cores and a remotely sited tuner fed via 200ft of low loss LDF2-50 coax vs. a broadband antenna of the same element length. 40-30-20 . Use with other lengths can potentially damage the transformer depending on power level in use. I used 2000 and 1000 ohm resistors in series connected to the proper unun wires with alligator clips for a total of 3000 ohms. 49:1 impedance transformer UNUN - Wire Antennas Lengths of a half-wave or multiple must be avoided. A 9:1 unun is a transformer that reduces the impedance at the input by a factor of 9. rig, often with no feedline, and the other end in the air attached to Well, I didn't think it would make any difference at that many multiples. I will also find some sort of heat resistant packing material to help hold the transformer in place. Having the option to switch rapidly between 49:1 and 64:1 should prove to be a really nice feature..