MFJ MFJ-911 User Manual

MFJ-911 4:1 Current Balun/Unun Instruction Manual

MFJ-911 4:1 CURRENT BALUN/UNUN

1.8-30 MHz

INTRODUCTION

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.

INSTALLATION

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.

High voltage can be present at the binding
posts of this unit. Install it where these posts
cannot be inadvertently touched.

WARNING

Transmitter or

Figure 1
Block Diagram

transceiver

External antenna

tuner

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MFJ-

911