After many requests we have created a compact, special balun for OCF antennas with vertical radiators. The CB-4-1500ODCV is a CUBE™ enclosure containing a dual core, bifilar wound, voltage balun to force equal voltages on the unequal sides of the off center fed antenna and force current down to the vertical radiator so it acts like a vertical antenna adding to the radiation pattern at low angles for DX.
The vertical radiator is typically 10 feet of 50 ohm coax for the 40 meter long (67 feet at the top) and 22 feet long for the 135 foot OCF.At the bottom of the vertical radiator you should have a line isolator or 1:1 balun (such as the Palomar BA-8E or BA-58E sleeve balun, or CB-1-1500 cube balun) to stop the current on the outside braid of the coax from using the rest of your feedline back to the radio as a long vertical radiator causing RFI and other problems as well as skewing the radiation pattern. The balun can be used with any size.
The balun is rated for full 1500 watts PEP from 1.8Mhz – 61 Mhz and usable to over 150 MHZ! (see graph) The balun can be used with either a 50 or 75 ohm coax vertical radiator and feedline.
The matching line isolator is the MC-1-3000 which should be used at the end of the vertical radiator.
To address separate solutions we have developed two separate RFI kits: one for HF (1.8-300 MHz) mobile installations and another for VHF/UHF (30-1000 MHz) mobile installations. Each kit uses the appropriate ferrite mix for the frequency range desired.