The following appeared on the QRP list. // KH2PZ
---------- Forwarded message ----------
To: <topband@contesting.com>
Date: Sun, 29 Sep 1996 12:00:34 -1000
From: William K Hibbert <wb2vuo@juno.com>
To: Low Power Amateur Radio Discussion <qrp-l@Lehigh.EDU>
Subject: The Inverted-L Antenna
Here's another posting from the BARK PBBS...Keith, WB2VUO
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Page 1
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 or
40].
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'
For bands above 40 Meters, an All-Wire Ground Plane can be constructed,
but
that's another wire antenna project for the future. Give the Inverted
"L"
a try, and enjoy your limited-space MF/HF operation.
72/73, Keith, WB2VUO, QRP-L #582
Trustee, KB2YTW/B 10 Mtr Beacon (28.2860 MHz)
"In the Depths of the Great Bergen Swamp...FN13ac"
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