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 transformation. 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.
It should be noted that OCFD antennas were designed to provide low SWR for full power rating on even harmonics only, i.e. 80m, 40, 20m and 10m. Use on WARC bands or 15m can create SWR greater than 2.5:1 which degrades the power handling of baluns by 60% or more. Power on these bands should limited to a level not exceeding 500-700 watts ssb and 300-400 watts for FT8 or high duty cycle RTTY while on these odd harmonics.
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
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 our new Hybrid model 4116 which incorporates a 1:1 choke balun for higher feedline isolation and RF choking or the Model 4114ocf for legal limit power combined with a compromised installation. .
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 0.2db
|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.
4x4x2 inches for main body of unit
|Additional Info|| Very high efficiency (98-99%).