W6SDO.COM                                                  SAN DIEGO, CALIFORNIA USA
       160M INVERTED L

Another antenna added from the antenna
plan is a 160 meter ¼ wavelength inverted
L. A 130 foot length of 12 gauge PVC
covered stranded wire slopes up from the
ground system to the 40 foot level of the
45 foot tall fiberglass flagpole (about 60
feet of wire length) and then proceeds
about 70 feet toward the far back edge of
my property. The 90 foot start-to-finish
dimension just fits my city lot. At the end,
the antenna wire is terminated at about 15
feet above the level of the back yard. The
geometry actually resembles an inverted L
that has partially fallen over – in other
words, a “lazy L”. This antenna is used on
160 meters only and is coaxial cable fed.

In place of an active tuner, a 10 turn 4 inch
diameter tapped coil wound of 0.250 inch
diameter copper wire is used to tune the
1.8 to 2.0 MHz band in three segments.

Two vacuum relays are used to select the
correct amount of the coil for a particular
band segment. No coil turns are added to
the top band segment, 7 turns are
connected in series for the middle tuning
range and the entire coil is used at the
bottom end of the band. All of the base
load components plus the static discharge
arrestor are located in a 7 inch square
weatherproof box that is bolted to the
ground structure.

The coaxial cable entry point is sealed
with silicone sealant to keep the spiders
and moisture out. The wire that brings
power to the relays is TV rotor cable which
is rated to be used outside in the weather.

The transient suppressor and coaxial
cable braid bus-work is bonded to the
ground system with a heavy braid.

The cross-section of the metal drainage
ditch that is used as the ground system for
this antenna is shown below.

This metal drainage ditch is about 100
feet long and runs along the top of a five
foot high concrete block wall that defines
the eastern boundary of my city lot.  The
drainage ditch measures 12 inches wide
and 12 inches deep. All of the 10 foot long
metal sections are electrically bonded
together along the length. This provides a
very good earth ground for this 160 meter
1/4 wave inverted L antenna as well as a
reflector / ground reference for the
75/60/40 meter NVIS antenna that is
mounted directly above the metal ditch
(see the NVIS page for more details about
this antenna).

An improvement that I am considering for
the ground system is to add a couple of
wire radials in addition to the drainage
ditch ground system.  These radials will be
run underground by fishing them through
the drainage pipes buried under my
driveway and front lawn. I think I'll connect
them with a remotely controlled relay so
that I can more easily quantify their
usefulness during actual on air contacts.

Another improvement under consideration
is to add a number of 10 foot long ground
rods along the length of the metal drainage
ditch, especially near to the antenna feed

Since my back of the envelope calculations
indicate that this antenna is only about
35% efficient (at best), these combined
improvements could potentially yield as
much as another 1 to 2 db of signal
strength at the receiving end of my
transmitted signal. Very interesting??

From there it proceeds up to a point about
five feet from the top of the 45 foot tall
fiberglass flag pole. This places the 160
meter antenna five feet below and at about
30 degrees crosswise to the OCF Windom
antenna wire to minimize interaction
between the two antennas.

The far end of the antenna is attached to t
he fence with a pulley and one gallon paint
pail counter weight that takes the sag out
of the antenna wire and allows the antenna
pole to sway freely with the wind without
stretching or breaking the antenna wire.

The maximum SWR at the edges of each
of the three segments is less than 2.5:1. At
1.945, the frequency that I use the most,
the Rs measures 33 ohms with an Xs of 32
ohms for an SWR of about 1.9:1  according
to my MFJ-269 analyzer.

Since the static discharge protection is
located at the base of the antenna, the
coaxial feed line goes directly to the shack
through a 100 foot length of coaxial cable.
The antenna loads nicely and shows
virtually no change in SWR when operating
in either dry conditions or on a rainy day.

The antenna handbooks show that the
inverted L has a more or less  omni
directional pattern that is uniform within
about 1.5 db. The signal reports from any
direction using this antenna are always as
good as or better than the signal reports
for other hams using top loaded verticals,
full wave loops and dipoles at similar
heights. This antenna is not a multi-element
full size vertical array using massive
towers, but it does work and works quite
well. This is the one band where I often
run the full power in order to overcome the
very noisy band conditions that are typical
at the receiving end.

160 meters is also the band where the 38
inch diameter magnetic loop antenna
(pictured at the left) really shines. This
loop  often delivers the best quality
receiving signal, especially if there are
plasm TVs operating in the vicinity (see
the PIXEL loop page for more details
about the performance of this loop on the
160 meter band).

  Last Revised December 10, 2012
Photo above: Base loading coil
assembly that is used to tune the two
lower frequency segments of the band.
Coil segments are selected by two
vacuum relays. A surge protector is
attached to the end of the coaxial
cable feed line.

The antenna wire coming from the
weatherproof box mounted on the metal
drainage channel (lower center of the
photo) first goes up to the top of the brown
painted PVC pole (at the upper right of
the photo),