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Balun Designs

Model 4115ocf - 4:1 for OCF Dipoles 1.5 - 54 MHz 5kW


Model 4115ocf - 4:1 for OCF Dipoles 1.5 - 54 MHz 5kW

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Product Description

This design is built by winding individual cores as 1:1 choke baluns (100 ohm characteristic impedance) and then cross connecting them.  This creates a 4:1 current balun with excellent feedline isolation, very high RF choking and virtually perfect impedance tranformation. A very good choice to build an Off Center Fed dipole around, but please note the caution statement below.

This model should NOT be used for a traditional Windom dipole that has a vertical coaxial radiator.  Instead, use the model 4125et to allow RF to pass to the vertical coax.

If you look closely at the images, you can see the individually wound cores that form the balun. Each core has 10 individual turns to generate maximum choking impedance and produce near perfect transformation. The black polymer spacer is used to insure proper separation of the individually wound cores at all times. The balun includes the Top Eyebolt so you have a complete package for your antenna project. Please review the test scans below to appreciate the excellent specs this balun offers.

Click to Enlarge

All testing done with an AIM-4170c Network Analyzer and precision 200 ohm load

Ready made pre cut and crimped antenna wire for this balun can be purchased at s9-logo-thumb2.jpg 



If one or both legs of your OCF dipole will be installed over or close to (< 20 feet) your house, a large structure (garage, barn, etc) or near (< 30 feet) a metal roof/structure and you will be transmitting greater than 700 watts CCS,  DO NOT use this 4115ocf balun.  The interaction/coupling of the antenna with the structure and or metal will require high levels of common mode absorption by one ferrite core which will generate excessive heat in the core leading to a change in SWR and possible damage to the balun. Instead use the Model 4114ocf which utilizes a set of stacked cores designed to handle the imbalance caused by any interaction or coupling.

There are a number of interesting designs for OCF dipoles available on our website 
listed under Antenna Design Links on the
Support & Downloads tab at the top of the page. 



  Core Material   Custom mix low permeability ferrite by Fair Rite Products for maximum bandwidth.
  Cores are coated and sealed for long term durability.
  Winding Type   Individual cores wound with single wire pair as 1:1 current balun.
  Cores are then cross connected to create 4:1 current balun.
  Winding Material   Bifilar windings of 14 gauge Heavy build polyamideimide Allex 240 Winding Wire
  Windings are inserted into Teflon tubes increasing total breakdown to 10,000 volts.  
  Power Rating   1 to 35 MHz - 5kW, 7kW intermittent.  35 to 54 MHz - 4kW.  
  All ratings based on resonant load. High SWR will reduce power handling ability.
  Useable Frequency   1 to 54 MHz
  Insertion Loss   Less than .02db
  Connectors   SO-239 connectors are gold center conductor with Teflon insulation.
  Studs and eyebolts are 1/4 inch.
  Alternate connectors and Mounting Options are available in the Accessories section.
  Hardware   All Stainless Steel
  Enclosure Type   NEMA rated 4x marine grade junction box for outdoor installations.
  Cover utilizes integral neoprene gasket for weatherproof integrity.
  Dimensions   4x4x2 inches for main body of unit
  Additional Info   Very high efficiency (98-99%). 

Installation Notes