Off Center Fed (OCF) Antennas

Multi Ratio 2.25:1/4:1/9:1 CUBE™ Unun, 3-31 MHz, 1.2KW Watt, vertical, end fed

SKU CU-2-4-9-1200
In stock
Product Details

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:

CU 2.25 4 9 600 Graph 1024x639 - Off Center Fed (OCF) Antennas

The Unun provides multiple taps for impedance conversions of:

  • 50 to 450 (9:1) – for end fed long wires, traveling wave antennas
  • 50 to 200 (4:1) – for ¼ wave vertical folded dipoles, OCF verticals
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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,