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4:1 Balun/UnBal - 300 Watts

The MFJ-911 is a true 4:1 current balun/unun that transforms 200 ohm balanced and unbalanced loads to 50 ohms. The response is amazingly flat from 160-10M because it is a true Transmission Line Transformer using 100 ohm characteristic impedance transmission line. Two low permeability ferrite cores are used to easily handle 300 Watts. Chance balanced to unbalanced operation with handy ground post. 2½ x 4¾ x 1 inches.
The MFJ-911 is a true 4:1 current balun/unun designed for indoor use. It uses large lowpermeability ferrite cores to transform 200 ohm balanced or unbalanced loads to 50 ohms, and is rated at 300 watts with relatively flat response from 1.8 to 30 MHz. Its SO-239 coax connector has Teflon™ internal insulation for maximum insulation and extended life of the product. 2-way binding posts provide for convenient hookup.

A current balun can reduce or eliminate stray RF often found on coax. This stray RF can cause
burns and other problems with electronic equipment while reducing antenna radiation.
Installation of an MFJ-911 balun can increase the efficiency of any amateur station.

High voltage can be present at the binding
posts of this unit. Install it where these posts
cannot be inadvertently touched.
1. The MFJ-911 is intended for applications protected from the elements – out of the weather.
2. For use as a balun (balanced load to unbalanced) connect the balanced feed line to the red binding
posts and the coaxial cable to the SO-239 coax connector.
3. For use as a unun (unbalanced load to unbalanced), install a jumper as indicated on the unit. Connect the unbalanced feedline to the binding posts, ensuring that the center conductor is connected to the binding post that is not grounded and the shield is connected to the grounded binding post.
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