OCF antennas are very convenient as they will allow multiple bands of operation with a simple wire antenna which is fed off center with a 4:1 OCF Current balun with built in feed line choke,
Model CU-2.25:1-4-9-1200 is a 2.25:1, 4:1 and a 9:1 voltage unun housed in a NEMA enclosure box (4" x 4" x 2") with one stud for 2.25:1 (112.5 ohms), one stud for 4:1 (200 ohm load) and another stud for 9:1 (450 ohm load) outputs, each capable of input power levels up to 1200 watts PEP when used with a matched load. (You can only have 1 load connected).
The 2.25:1 ratio takes 50 ohm input and matches it to a 112.5 ohm load (useful for 100-150 ohm antenna load). The 4:1 ratio takes 50 ohms input and matches to 200 ohms output and the 9:1 ratio takes 50 ohm input and matches to 450 ohms output between 1-31 MHz under 1.5 SWR under matched load conditions.
A great multi-purpose unun for 31 or 43 foot fiberglass verticals, end fed non-resonant antennas, traveling wave verticals, etc. Quad core, Ruthroff style unun with side ground terminal for adding a counterpoise or radials as an option. Now you don’t need to buy three separate ununs – just buy the CU-2.25:1-4-9-1200 and pick the output ratio that provides the best match for your antenna tuner!
Impedance transformations from 3-30 MHz are shown below:
The Unun provides multiple taps for impedance conversions of: