Kg3v Ham Radio Blog

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160 Meter Inverted "L" Antenna

Posted: 02 Aug 2020 04:51 PM PDT
https://kg3v.com/2020/08/02/160-mete...ted-l-antenna/


I have a need to get on 160m occasionally for a contest, but have limited
space. I tried a dipole, but it was just too much trouble. I had to bend
the ends all around to fit my small lot. I keep hearing that an Inverted L
is a decent antenna, but have never been fond of laying radial systems. The
vertical antenna I have has less than 8 radials that is just the way it is
going to be.

I wont bother posting a graphic of this antenna, they are everywhere. If
you want the design details, just Search on it, or go to the ARRL Antenna
Book or any of the many great reference Sites and books out there. Here is
one link, if you really want to dig into 160 meter antennas of all kinds.
This is a presentation by Jim Brown K9YC. His material is always worth
reading and digesting, and he is a recognized expert on EMI/RFI in the Ham
Radio world.

When I started this project, I was still thinking about a long antenna. It
turns out that this is now the shortest wire antenna (horizontally) that I
have. Shorter than my 80 meter Broadband dipole, shorter than my ZS6BKW. In
fact, it turned out to be much shorter than the distance between the two
trees I had planned to use as supports.

The formulas say to use a horizontal section of around 80-90 feet. I always
start long with wire antennas, so I get to cut when tuning, and do not have
to worry about adding wire. I began with a total length of 135 feet, with
about 90 feet on the horizontal leg. I only added two radials, and they are
both very short, probably about 66 feet long. I also used a ground rod and
a 1:1 balun for conveniently connecting my coax for the run to the shack. I
have about 30 feet of coax, and have a few ferrite beads on about 5 turns
of the DXE-400MAX coax, just before it enters the house.

Here is an SWR plot of the first attempt, with total length of 135 feet:



As you can see, the SWR min is too low in frequency, which is to be
expected, given the length. This was good enough for me to use it in the
NAQP CW contest this weekend (which started 30 minutes before I completed
this antenna), with my Antenna Tuner. After the contest, I will trim it, to
get a larger portion of the Band within the 3:1 SWR range, as needed by
most rig-internal tuners.

After a couple cuts, and measurements, I got the length down to about 127
feet total length. I have the vertical section about 40 feet long, and it
is not exactly vertical but slopes from a tree to my balun about 3 feet
above the ground. Here is the resulting SWR curve:



I can definitely live with this for now. In most contests, the activity
seems to be in the lower portion of the Band. I may do some more pruning,
but for now, this will work. And I will add more radials sure I will

The original (135-foot long) antenna worked quite well in the contest. I
got 16 State multipliers and about 50 QSOs in the last hour or so of the
contest. So this will be staying in my antenna collection. I will try to
add a few better radials, maybe..

I did have one minor issue. It seemed like I was getting some RF into the
shack, and PC acted a little strangely at one time. I need to improve my
EMI filtering on some of the lines entering the shack, to make sure I am
choking common-mode RF in the 160 meter Band.

If you have the room, I always hear that a full-wave loop is a great
antenna for 160 meters. That is just not going to happen on 160 at this
location.

Thanks for stopping by, please leave comments or questions if you have time.