Model 1151 - 1:1 ATU Current Balun, 1 - 54 MHz, 2kW

This new release provides excellent choking and feedline isolation across the full HF spectrum, but is a departure from the normal 1:1 isolation/choke balun.  Rather than a 50 ohm characteristic impedance, this balun 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.  The 1151 is ideal for moderate power operations, is lower in overall weight and provides outstanding performance.  This balun is also excellent when installed between a remote auto tuner and multiband antenna to suppress common mode allowing a cleaner more accurate match. Use with coaxial fed monoband wire or beam antennas is NOT recommended.

IMPORTANT: This balun is NOT wound with the normal 50 ohm pair, rather the design criteria is maximizing inter-conductor breakdown voltage which results in a 97 ohm pair.  Consequently, this balun is intended primarily for use with ladder line/open wire fed multiband 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. 

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
http://www.karinya.net/g3txq/tuner_balun/

 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.

- Ability to generate 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.

Specifications

Installation Notes