Article and Website By KN4LF
I decided to publish this website in order to pass on
some insights about this antenna that I've garnered through extensive
experimentation. Warning though some of the combined design aspects of the
antenna may be unique and definitely unorthodox. Note! I do not have a B.S. or
M.S. in EE so some of my antenna theory explanations may be incorrect.
First of all here are some
of my recent QSO's as an example of how this antenna performs
using just 100 watts:
MM/DD/YYYY UTC STATION COUNTRY MODE RCVD RST/RS
January 30, 2006 0203 UTC OK1VSL Czech Republic PSK31 559
January 31, 2006 0035 UTC G3FPQ England CW 569
January 31, 2006 0210 UTC SM4CAN Sweden CW 559
February 02, 2006 0331 UTC SP3BQ Poland CW 559
February 06, 2006 0345 UTC SM5IMO Sweden CW 449
February 06, 2006 2338 UTC I4EWH Italy CW 559
February 09, 2006 0443 UTC UR0MC Ukraine CW 559
February 21, 2006 0009 UTC J79IX Dominica CW 599
February 22, 2006 0325 UTC OM2XW Slovakia CW 559
February 22, 2006 0436 UTC YO2LDC Romania CW 579
February 22, 2006 0446 UTC SV3RF Greece CW 569
February 22, 2006 0513 UTC HB9ATA Switzerland CW 579
February 23, 2006 0415 UTC IV3PRK Italy CW 559
February 23, 2006 0437 UTC OH2BO Finland CW 569
First of all here are some of my recent QSO's as an example of how this antenna performs using just 600 watts:
March 4, 2006 0421 UTC RK2FWA Kaliningrad Russia SSB 59
March 4, 2006 0512 UTC HA5JI Hungary SSB 59
March 4, 2006 0526 UTC Croatia SSB 59
A physical description of the antenna is as follows:
The total length of the inverted L is 240 feet, which is 7/16th of a wave length long. It has a 92 foot horizontal linear load section 1 foot above ground that terminates into a homebrewed parallel network tuner, a 50 foot vertical section and a 98 foot flat top. The 89 foot horizontal linear load section increases radiation resistance and therefore transmit efficiency compared to a conventional loading coil, the 98 foot flat top pulls the highest current point 25 feet above ground level on the 50 foot vertical section, for lower capacitive coupling ground loss.
As far as wire I use black UV resistant double coated stranded #14. The wire is lightweight, has less resistance in windy weather and nearly invisible to the naked eye. The last one foot of the end of the antenna comes directly into the shack to the home brewed parallel network tuner. I also have an MFJ-931 ground tuner tied to the ground side of the parallel network. With it I tune one 124 foot radial on the ground outside to resonance for the inverted L to push against so to speak.
If you want to read about vertical antenna theory
including return current grounding, elevated highest current point, etc.
I cover allot of
theory on my other antenna website at
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I've done extensive experimentation with radials
on vertical antennas on 160 meters during the past 18 years.
Back in 2001 a MF broadcast engineer friend of mine using professional broadcast
measuring equipment, took near field measurements of the electric field in V/m
RMS. The antenna was a 1/4 wave inverted L with a 64 foot vertical section and
(1/8 wave) 64 foot long radials laying on the ground surface.
I found the following:
There was little measurable difference between 0 and 4 radials, a small
measurable difference between 4 and 8 radials, a medium measurable difference
between 8-16 radials, a large measurable difference between 16 and 32 radials, a
small measurable difference between 32 and 64 and no discernable measurable
difference between 64 and 120 radials.
We then conducted another experiment using conventional (1/4 wave) 128 foot
radials and found the data to be exactly the same as the 1/8 wave radials. To me
this proved the theory that the radials need not be any longer than the vertical
section is tall.
I have never had the opportunity to do the experiment with a full 1/4 wave
vertical.
This statement will be controversial. Using a voltage fed electrical 1/2 wave
tee antenna with a 64 foot vertical section and three 200 foot long
top hat wires, in the near field we measured only a very small difference
between 1 radial and 64 1/8 wave radials. We measured no difference between 1
radial and 64 1/4 wave radials.
The ground conductivity was pretty good at the location of the experiment. It
was a typical Florida hammock swamp that had been filled in but always had black
mucky soil and a high water table. The conductivity was approximately .03 S/M
with a dielectric constant of approximately 20. I've always presumed that the
results might be different over ground with poor conductivity.
Note! When it comes to 160 meter vertical antenna's you can get a lower take off angle (TOA) from a full 1/4 wave vertical or electrical 1/4 wave tee vertical of 10-20 deg., versus ~30 deg. with the inverted L. However it's a moot point as the night time E layer MUF blocks 160 meter low angle transmitted radio signals from ever reaching the F layer to be propagated. So unlike with HF propagation, MF propagation success does not require the lowest of take off angles.
Also higher take off angles of ~30 deg. via the inverted L are better able to take advantage of the low signal loss E valley-F layer propagation duct mechanism, a form of Chordal hop propagation.
If you have the EZNEC antenna modeling software and want the .ez file for this antenna send me an email to the address on QRZ.com.
Your particular configuration will most likely be different than mine, with the golden rule being that you want to get as much wire in the vertical section of the inverted L as possible and also have the highest current point near the middle of the vertical section for low angle long haul DX contacts.
As follows is a diagram of the antenna layout. Leg's #1, 2 and 3 have no appreciable radiation like a coil but without the losses.
#1 leg is a 38 foot horizontal linear loaded section one foot above ground and broadside north-south.
#2 leg is a 43 foot horizontal linear loaded section one foot above ground and broadside east-west.
#3 leg is an 11 foot horizontal linear loaded section one foot above ground and broadside north-south.
#4 leg is the 50 foot vertical section.
#5 leg is a 60 foot horizontal section 50 to 45 feet above ground and broadside NNW-SSE.
#6 leg is a 38 foot horizontal section 45 to 40 feet above ground and broadside ENE-SSW.
I came up with this configuration as
EZNEC 4 said it provided the lowest take off angle with the most omnidirectional
pattern, highest far field signal strength and placed the highest current point
in the middle of the vertical section. The antenna is supported by a 50 foot Rohn
telescoping push up pole and available oak trees on my near 1/2 acre lot. Please
excuse the crappy artistry.
As follows are some images of the 38+43+11=92 foot
horizontal linear loaded sections one foot above ground. I used 1/2" schedule 40
PVC pipe with 3" antenna insulators for mounting.
You may ask why I bring the near end of the inverted L directly into the radio shack (only one foot) instead of running a coaxial feedline outside to the feedpoint of the antenna? There are several reasons:
1.) With no coaxial feedline there are no feedline losses to worry about.
2.) The home brewed parallel network antenna tuner actually tunes the antenna, in my personal opinion.
3.) The antenna has a high Q and therefore narrow bandwidth and I don't want to have to design a remotely tuned antenna tuner at the antenna feedpoint in order to QSY around on the 160 meter band.
4.) Multiband use of the antenna. I switch an old and well designed MFJ-989B antenna tuner in line and work 80-10 meters with increasing gain as I go higher in frequency. I have one 1/4 wave resonated radial for each band and this prevents stray RF from bouncing around in the radio shack.
Speaking of multiband use here is what EZNEC says about take off angle of the highest current and gain in dbi.
1.845 kc 30 deg. 1.63 dbi
3.580 kc 85 deg. 7.28 dbi
7040 kc 70 deg. 6.73 dbi
10.137 kc 50 deg. 5.42 dbi
14.080 kc 30 deg. 6.02 dbi
18100 kc 20 deg. 7.14 dbi
21.080 kc 20 deg. 8.62 dbi
24.900 kc 15 deg. 6.79 dbi
28.120 kc 15 deg. 6.98 dbi
I have usable low take off angle performance on all bands except 80, 40 and 30 meters, though I seem to be able to work anywhere I want on those bands. On 20-10 meters there are enough smaller lobes that work to give me pretty much an omnidirectional pattern.
73 and GUD DX from KN4LF.
Visits Since 08/31/2005