MFJ MFJ-1777 User Manual

MFJ All Band Doublet Instruction Manual

MFJ-1777 All Band Doublet

INTRODUCTION

The MFJ-1777 is a multi-band center-fed dipole antenna capable of handling
1500 watts. It consists of a 102-foot “flat top” antenna fed with a length of 450
ohm balanced “ladder line.”

This antenna requires the use of a suitable matching network (antenna tuner)
with provisions for balanced-feed antennas, for interface with the 50-ohm
unbalanced antenna outputs of modern transceivers and amplifiers.

This antenna will work as supplied, as a centerfed antenna, on all amateur bands
80 through 10 Meters. On 160 Meters it can be used as top loaded vertical
antenna, with the dipole element acting as a capacitance hat on 160 meters (see
“160 Meter Operation,” page 3). Operation on 160 Meters in this manner
requires a ground screen or radial ground system, which is discussed on page 4.
This antenna will not work effectively in its center-feed configuration on 160
Meters.

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
suitable structures or trees If trees are 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 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 has
detailed suggestions for installing wire antennas.

WARNING: Always mount antennas so that they are out of

the reach of adults and children. Contact with any part of

this antenna can cause RF burns or other injuries.

See the Safety Precautions on page 7.

1

MFJ All Band Doublet Instruction Manual

INSTALLING THE ANTENNA

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: Requires two tall supports separated by more than 102
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.

Try to keep the antenna as horizontal as possible. The antenna must be more
than 35' above ground level to give acceptable performance, and as high as
possible for the best overall performance. The ladder line should drop vertically
from the horizontal section for at least 20 feet and should be kept several inches
from conductive objects. If the antenna's ladder line has to be installed near
conductive objects, space the line at least 6" from the object with non­conductive supports (for example: PVC pipe standoff supports 6" long). Use
nylon cable ties to secure the feedline to the supports.

Be sure to allow enough slack or use some type of pulley and counterweight
system to prevent the antenna or rope from breaking if the trees move in the
wind. It is also possible to use masts, towers, or other tall structures for
supports. Try to keep the ends of the antenna at least

supports.

IMPORTANT: Use weather resistant rope rated at

at least 50 pounds working load to support this antenna.

five feet from metallic

Inverted "V" Antenna: This method requires only one tall support and also
places the least strain on the antenna. Hang the center insulator of the antenna
from the support using a nylon rope or other non-conductive rope tied to the
center hole of the center insulator. The center insulator should be the highest
point of the antenna. The antenna ends should be less than 25.5 feet below the
center insulator. This avoids an inside angle of less than 120 degrees between
the antenna's legs. The antenna ends should be secured with nylon or weather
resistant non-metallic rope to suitable supports.

Sloper Antenna: This antenna can also be suspended as a sloping dipole. This
requires one tall support and one short support. The center of the antenna must

2