This is a design I found and it works right from the start. I built it for 160
meters using 14 gauge stranded bare copper and
have great results. The feed point is made from aluminum L stock. Drill a hole
for a panel mount SO-239(not chassis) to fit.
Do not directly connect the vertical element to the SO-239. The first strong
wind will rip it apart. To address this,
anchor the vertical element to the tree using an insulator, rope and then a lag
eyebolt into the tree. This will secure your
vertical end so you can safely solder a wire to the center pin of the SO-239
and the wire without straining the feed point.
Connect the elevated (10') counterpoises to the aluminum plate with a terminal
lug and self-tapping screws. Extend the
counterpoises and support them along the way by affixing them to a tree with
electric fence post insulators. They are
perfect for this application. I have attached photos of the feed point idea
and the insulators. I suspect the server strips
the attachments. Scott, I emailed you direct so you will have the photos.
Here is a copy of the text from the document, by WA2VUO.
The Inverted "L" Antenna
So, you REALLY want to get on the 160 Meter band, but the neighbors won't let
you run your 250' long
dipole over their swimming pool? And, you say that the State DOT looks down on
your attempt to tie the other end across the
State Highway? Well, fear not, as there is a compact solution to your MF antler
woes, and it is an Inverted "L". [It can also
be cut for 80 or40].
The Inverted "L" is a 1/4-wave Marconi, fed against ground or a counterpoise
such as radials. The
antenna displays a low feed impedance, which allow you to feed it directly with
50-ohm coax cable. The vertical section
should be as high as possible, with the remainder of the antenna run
horizontally to a support, such as a tree or a mast. The
antenna is fabricated from wire, with the heavier the gauge the better. [The
larger the wire diameter, the wider the
bandwidth]. One method of installation would be to use a mast as the vertical
"wire", with the horizontal section firmly
bonded to the top of the mast. The wire is cut to a resonant 1/4-wave length,
based on the formula:
L(Ft) = 234/F(MHz)
If your ground is REALLY good, like your house is on stilts over the ocean, a
counterpoise won't be
needed, but for our GREAT ground here in Western NY, figure on using at least
one counterpoise, if not a few. The length of
the counterpoise wires will be cut to a 1/4-wavelength by the formula:
L(Ft) = 246/F(MHz)
Basically, the counterpoise should be high enough to not get in the way, but
could be as high as your
installation allows. Mine is run around the base of the house, just below the
siding, except around the back door. At that
point, I ran the wire under the bottom of doorframe. The wire I used is #18
stranded insulated hook-up wire.
CHARTS
Well, any antenna discussion is not complete without a chart of some sort, so
here are the dimensions
for an Inverted "L", listed in tabular form:
Frequency Radiator Length Counterpoise Length
1.85 MHz 126.5' 133.0'
1.95 MHz 120.0' 126.2'
3.60 MHz 65.0' 68.3'
3.90 MHz 60.0' 63.1'
7.15 MHz 32.7' 34.4'
Anthony
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Scott MacKenzie
Sent: Sunday, September 19, 2010 19:26
To: towertalk@contesting.com
Subject: [TowerTalk] Inverted L Dimensions
I have decided to take the plunge and put up a simple antenna for 160M.
Several comments:
It has to be simple and not excessively expensive;
I have limited room for antennas on my lot, and very limited room for
radials.
I do have multiple tall trees that I can use to hoist a wire 60 feet + in
the air.
My soil, if you want to call it that, is poor and rocky (typical Eastern
PA).
My application is casual DXing and working stateside.
Based on this, it looks like an inverted L is probably my best choice. I
want to feed it with 50 ohm coax. Now the questions are pretty simple:
What dimensions are best - 5/16 or 1/4 wave? Both are indicated in the
literature.
What is simpler to match?
Am I better off making a loaded vertical approximately 60 feet long?
I appreciate your help.
Scott aka KB0FHP
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