MFJ MFJ-1748 User Manual

MFJ-1748 80-10 Meter End-Fed Zepp Instruction Manual

INTRODUCTION

The MFJ-1748 End Fed Zepp is an end-fed wire antenna that, when properly
erected and fed with balanced feedline through an antenna tuner, will be usable
on all amateur bands from 80 to 10 Meters. This antenna will handle 1500 watts
of RF power (with a suitable antenna tuner). Its total length is approximately
135 feet.

The name “Zepp” harkens to the days of dirigibles, or Zeppelins, which used
trailing wire antennas that, by definition, had to be fed at one end.

The antenna is 135 feet long, a half-wavelength at 3.5 MHz (for convenience,
think of the center of the 80 Meter band as roughly 130 feet, and 4.0 MHz as
about 125 feet). End-feeding a half wavelength of wire on 80 meters has certain
mechanical advantages over center-feeding the same length of wire. It can be
erected in limited space situations where a 135-foot centerfed antenna is not
possible.

The disadvantage of end feeding is that tuning is related to feedline length. The
general rule of thumb is that feedlines that are a multiple of a quarter­wavelength for any given frequency band may present tuning difficulties on that
band. If you need to add feedline to this antenna, feedline lengths near 65 feet,
130 feet, and so on, should be avoided for ease of tuning on the 80 meter band.

Note these approximate quarter wavelengths, in feet:

80 Meters – 65
60 Meters – 48
40 Meters – 32
30 Meters – 28
20 Meters – 16

Clearly, there is no magic length of feedline that will avoid being a multiple of
at least one of these lengths! In some cases, the end-fed zepp may tune better at
one end of an amateur band than at the other. As with every antenna, the zepp
will always work best as far away as possible from any metallic objects.

In addition, care should be taken to route the feedline vertically away from the
feed point as far as possible, and also to keep the feedline away from metallic
objects. These considerations are of somewhat greater importance for an end­fed antenna than they are for a centerfed antenna. Also, as with all antennas, the
higher this antenna is above ground, the less it will be affected by surrounding
objects and terrain.

17 Meters – 12
15 Meters – 8
12 Meters – 7
10 Meters – 6

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MFJ-1748 80-10 Meter End-Fed Zepp Instruction Manual

With a suitable antenna tuner, this antenna can be used on 160 Meters, by tying
the two sides of the feedline together at the tuner, and feeding the system as a
long wire.

Some may find it strange that in this antenna one side of the feedline is
connected to nothing at the antenna end. This antenna works because, while the
impedance at that point (where the feedline stops in dead air) is infinitely high,
the impedance at the other feed point is very high, especially at the design
frequency, in this case 80 Meters. So, the feedline is reasonably “balanced,”
since it sees a “high” impedance on both sides at the antenna feedpoint.

When the antenna is used at frequencies higher than the design frequency, in
some cases the feedline will become somewhat less balanced, resulting in
radiation from the feedline (RF in the shack).

A detailed discussion of antennas of this type can be found in ANTENNAS From
the Ground Up, by L.B. Cebik, W4RNL, published by MFJ Enterprises, and
also in the ARRL Antenna Book.

Assembly

This antenna comes assembled and ready to install using rope(s) for attaching to
support structures. The length of the antenna wire provided is 135 feet.
Operators interested exclusively in operation above 3.750 MHz may obtain
slightly smoother tuning by shortening the antenna. However, it is best to first
erect the antenna with the full length of wire provided, experiment with tuning,
then decide whether or not to prune it.

Installation

The best location for this antenna is as high and far away as possible from utility
wires, other antennas, and other structures. It is impossible to find a perfect
location, so the best compromise must be accepted. In order to perform
textbook-fashion the antenna must be installed as a horizontal antenna, as level
as possible.

Suspend the antenna with at least a 50-pound working load nylon rope or
equivalent strength weather resistant non-metallic rope. Never use wire or wire
core rope to support the ends of any antenna. Attach the rope to the end
insulators through the empty holes. The antenna should be at least 35 feet above
ground to give acceptable performance and as high as possible for the best
overall performance. The feedline should drop vertically from the horizontal
section of the antenna as far as is practical.

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