End-Fed Longwire Antenna with a 9:1 UnUn rated at 700 watts,
covering 160 meters through 10 meters, only 124' 6" long.
The following tables show the recommended lengths to use for antenna wire based on the bands you wish to cover.
across the HF frequencies will vary
based on topography, proximity
of nearby structures, configuration of
the antenna as an Inverted L will change
the feed point impedance due
to top loading and may
require changing the
you decide to install the UnUn in a high location, the use
of a counterpoise wire
is required as any long wire run to a ground
keep in mind this design is intended primarily for
those living in restricted antenna areas or for temporary or emergency
Recommended Wire Lengths (in feet) for 9:1 UnUn - 160m through 10m
53 59 72 88.5 98.5 124.5 135 146 162 175
Values in Blue are best overall lengths to use for optimum HF spectrum coverage.
SWR for all lengths should typically be under 2.2:1 and in most cases will be under 1.8:1 for 160m - 10m.
Built in and external antenna tuners will match the antenna on all bands.
by slightly by changing
the wire length (+ or -)
is encouraged to provide the best overall performance for
If you have difficulty obtaining an acceptable SWR on all bands, consider using one of the alternative lengths shown in the table below.
Alternative Lengths (in feet) for both 4:1 and 9:1 UnUns - 160m through 10m
58 71 84 107 119 148 203
your need for band
is limited to 40m through 10m, shorter antenna lengths
44 and 49 feet may also
design, UnUns are wound in such
a manner that they provide minimal or
no RF choking. Although
not necessary, a 1:1 isolation / choke
length counterpoise wires can be used
of operation is confined to 40m or higher.
should be at least 1 foot above
ground running away
from, or perpendicular
to the antenna wire.
Do not ground the counterpoise stud when using a counterpoise(s) or radial field!
Counterpoise wire(s) close to or laying on the ground will couple and become radials and will reduce antenna efficiency.
You may also use the UnUn with no counterpoise or ground if your feedline is at least 25 feet long or longer.
In this configuration, the coax shield will act as your counterpoise and there should be no ground at the UnUn.
this configuration, there
is a high probability of common mode currents
on the coax shield, so a good 1:1 choke balun should be installed
a counterpoise stud to a radial field
of 8 wires
minimum, each 10 to 20 feet
long. More is better and will increase the antenna's efficiency.
Attach a counterpoise stud on UnUn to a good ground rod at the feed point of the antenna.
the balun enclosure is weatherproof, connectors are not. Be sure to
coax connections in coax seal or your favorite weather