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Balun Designs

Model 1161 - 1:1 ATU Current Balun, 3 - 54 MHz, 5kW


Model 1161 - 1:1 ATU Current Balun, 3 - 54 MHz, 5kW

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Product Description

This is a departure from the normal 1:1 isolation/choke balun and utilizes a bifilar pair designed to maximize inter winding breakdown voltage. The balun functions to transform balanced twin lead, ladder line or open wire to unbalanced coaxial feedline while providing high levels of choking impedance to stop common mode currents from entering equipment.

Cores utilized in this model are optimized for mid to upper HF frequencies.  See the model 1171 for cores optimized to the lower HF bands.

This balun is NOT wound with the normal 50 ohm pair, rather the design criteria is maximizing inter-conductor breakdown voltage.  Consequently, this balun is intended primarily for use with multiband wire antennas such as doublets and loops where there will be a wide range of impedance values generated across multiple bands and with a tuner required for the final match.  Use with coaxial fed monoband wire antennas is not recommended.

Choking impedance for this balun has been shifted to provide maximum performance on the 40m through 6m bands. However, this ferrite mix also provides good common mode control on the lower HF bands if required . It is best installed outdoors to minimize the chance of RF entering the operating position from the balanced feedline.

Typically this balun is utilized with a tuner that can easily match a wide set of impedance values.  If you have a tuner with limited range, consider using the Model 4114 balun to reduce the required impedance match and thereby assist the tuner.   Click on the graph below to view the full choking impedance curve.

Click to Enlarge
Testing done with an AIM-4170uhf Network Analyzer

For a good graphical explanation of why this design works well, read through Steve's (G3TXQ) website page


 Design Criteria

- T match antenna tuners perform quite poorly if the resistive component of load impedance is very low, even worse if there is also a high capacitive reactive component. This is a common load found in shortened dipoles fed with open wire line.

- The traditional approach is to use a 4:1 balun on such antennas, but antenna tuner loss is worse with low resistive loads.

- The need to tolerate high voltages occurs when the balun happens to be located near a differential voltage maximum.

- Generation of high choking impedance for effective reduction of common mode current.

- Balun is intended for use with an antenna tuner which will manage SWR and transformation mismatches.

- Differential insertion loss is not significant in this application, the dissipation in a current balun is primarily from the common mode current which is installation dependent and not easily predicted.


  Core Material   Custom mix ferrite from Fair Rite Products optimized for low frequencies.
  Large 2.4 inch cores are coated and sealed for long term durability.
  Winding Type   Bifilar pair - 1:1 current balun, Stacked dual core provides larger effective core.
  Winding Material   Heavy gauge Essex polyamideimide Allex 240 Winding Wire wire inserted in teflon tubes.
  Breakdown voltage in excess of 10kv
  Power Rating   1 to 31 MHz - 5kW, 8kW intermittent.  32 to 54 MHz - 3kW, 5kW intermittnet.  
  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
 Dimensional Drawing of Standard Enclosure
 Additional Info  Very high efficiency. 
 Will not heat up or saturate at like many of the "less expensive" designs.

Installation Notes