MFJ MFJ-1778M User Manual

MFJ-1778M G5RV JR.

40m through 10m Antenna

INTRODUCTION

The MFJ-1778M antenna is a multi-band center-fed dipole antenna capable of
1500 Watts. The MFJ-1778M consists of 52 feet flat-top fed with 17 feet of 450
ohm matching section ending in an SO-239 coaxial connector.

This antenna generally requires the use of a suitable matching network (antenna
tuner) since the SWR of the G5RV JR is almost certainly not 1:1 on any band.
The use of a tuner will guarantee maximum performance from solid-state
exciters.

The MFJ-1778M is a balanced antenna that is fed by an unbalanced coaxial line.
This feed system causes unwanted parallel RF currents to appear on the shield of
the coaxial feedline. A choke type balun such as the MFJ-915 should be used
with this antenna to eliminate or reduce the undesirable parallel feed line
currents. Failure to use a choke balun may result in RFI, RF feedback, or other
symptoms of RF "in the shack". The Balun Requirement section describes how
to construct a choke balun for this antenna.

WARNING: Always mount this antenna so that it is out of the reach

of adults and children. Contact with any part of this
antenna can cause RF burns or other injuries.

TOOLS AND TIME REQUIREMENTS

This antenna requires no assembly. The time needed for installation will vary
with your skill and equipment.

No special tools are required to install this antenna. Nylon ropes are needed to
support the ends of the antenna from a suitable structure or tree. If a tree is
used, you will need a way to get ropes over it. The most common method is to
use a weighted arrow or a fishing rod and a heavy sinker to place a small line
over a tree. A larger line is then pulled up and used to pull the support rope over
the tree. The ARRL Antenna Handbook
wire antennas.

has detailed suggestions for installing

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SAFETY PRECAUTIONS

WARNING:

- This antenna is an electrical conductor. Contact with power lines
can result in death or serious injuries. Do not install this antenna
where there is any possibility of contact with power cables or the
service drop. The antenna should not be close to power lines
during installation, operation, or removal.

- Keep this antenna out of reach of adults, children, and animals.

- Any contact with this antenna while transmitting can cause RF
burns.

- Never place this antenna close to electric power lines or utility
wires.

INSTALLING THE ANTENNA

Please read the following suggestions and examples.

The best location for this antenna is as high and far away as possible from utility
wires, other antennas, and other structures. It is difficult to find a perfect
location, so the best compromise usually must be accepted.

The antenna can be installed in three basic ways:

Horizontal Antenna

This method requires two tall supports separated by at least 52 feet. Suspend the
antenna with at least a 50-pound working load nylon rope or another equivalent
strength weather resistant non-metallic rope. Never use wire or wire core rope
to support the ends of the antenna. Attach the rope to the end insulators through
the empty holes.

Important: Use weather resistant rope rated at a minimum of 50 pounds

working load to support this antenna.

Inverted "V" Antenna

This method requires only one tall support and also places the least strain on the
antenna. Hang the antenna from the support using a nylon rope or other non-

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