Sub Ratio (<1:1) Transformers
Sub Ratio Impedance Transformers
Available as Ununs (unbalanced to unbalanced load) or as baluns (unbalanced to balanced load)
Ununs are used between unbalanced coax to unbalanced antennas such as verticals, end feds and helical verticals which are shorter than 1/4 wavelength and exhibit a load impedance < 50 ohms. You can determine your antenna impedance by measuring with an antenna analyzer. The objective of the matching unun is to match the 12.5 – 25 ohm range antenna impedance to the coax 50 ohm line (the ratios of coax line impedance to load are also applicable for 75 ohm coax).
The impedance matching transformer (unun) should be placed at the antenna feed point and a feed line choke should be placed between the matching unun and the coax. See Feedline Choke Selection for alternatives.