MFJ MFJ-918 User Manual

MFJ-918 1:1 Current Balun Instruction Manual

MFJ-918 1:1 CURRENT BALUN

1.8-30 MHz

INTRODUCTION

The MFJ-918 1:1 current balun was designed to replace the center insulator of a dipole antenna.
It is made up of 50 ferrite core beads placed on a 13-inch length of RG-303 coax. The coax and
SO-239 connector have Teflon ™ insulation for maximum insulation and life of the product.
Unlike some other baluns, the MFJ-918 makes direct electrical connections to the antenna with
#14 copper wire. The balun is enclosed in Schedule-40 PVC pipe for maximum strength and
support of a dipole antenna.

The 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 the MFJ-918 current balun will increase the efficiency of any amateur station.

INSTALLATION

1. Place the balun on a suitable work surface.

2. Place approximately 4 inches of the antenna wire
through one of the eye bolts on the sides of the balun.

3. Loop the end of the wire back to itself.

4. Wrap the wire around itself 4 or 5 times to ensure it is
secure.

5. Repeat steps 2-5 for the opposite side of the antenna.

6. Wrap the lead wire from the side of the balun around
the antenna 3 or 4 times. Form a rain loop in this wire
to prevent water from entering the balun.

7. Carefully solder the lead wire to the antenna wire.
Excessive heat will damage the PVC pipe, so use
caution.

8. Repeat this process for both sides of the antenna.

9. Before the antenna is placed in its final operating location, check to see that the pull of
the antenna is exerted on the eyebolts of the balun and not on the lead wire. If enough
wire is left for the rain loop this will not be a problem.

10. Attach a suitable length of nylon rope or cord to the eye bolt on the top of the balun.
Make sure the cord is strong enough to support the weight of the antenna.

11. Always orient the balun so that the SO-239 coax connector is pointed down and water
will drain properly from the drain hole.

• Never install an antenna where contact with
power lines is possible. Death or serious injury
can occur if contact is made.

• Always install antennas out of reach. Serious RF
burns can occur if someone comes into contact
with the antenna during transmissions.

WARNING