|BACKYARD....CITY LOT ANTENNAs I have tried and worked on....ideas for you.
You will see below some scans I made from Articles from
Ham Radio Publications. These articles are ones that I have tried or am thinking of trying and I think
they are pretty good. (PARTIAL SCANS so as not to violate copyright restrictions (QST)
|AN INVERTED L ANTENNA WITH LOW FEEDPOINT IMPEDANCE (abt 90 ohms)
on two bands of choice. (80 and 40 version or 160 and 80 version possible) SEE JULY 1991 QST or
ARRL HANDBOOKS in the mid NINETIES for the original article by AE6C --- GOOD FOR CITY LOTS
|Below is the schematic and winding details for the broadband
bifilar transformer for a TWO BAND INVERTED L that will fit on
an average sized city lot. Iam on a city lot now and I have an
Inverted L up in the back yard. It works fairly well on 80 and 40.
Right now Im just using an MFJ tuner (random wire
configuration) to tune my inverted L. I have wound a T200-2
core as illustrated and tested it with a 90 ohm resistance with
my rf analyser and the circuit below works. The advantage
over using this circuit vs. a tuner in the shack would be to
keep the RF out of the shack.
I didn't have time to build the matching network at the base of
my inverted L (before the snow came) so..I just used my
inverted L with an Mfj tuner indoors and Ive had some good
results with it.
|Far End of the wire
antenna goes into the
upper branches of the
large tree at the back
of my yard. I used
brown insulated #14
wire (it is not too
|SEE JULY 1991 QST or ARRL HANDBOOK in the mid NINETIES for the original
article by AE6C
|This Inverted L works
pretty darn good. I feed it
with my MFJ tuner in the
It is about 100 feet overall
length. The feedpoint at
the end of the antenna
represents a fairly low
impedance on 80 and 40
meters (where I use it
I have a dedicated
matching network in the
works using a home brew
torroid coil 50 ohm to 90
ohm Z match.
Right now I use this wire on
all bands with an MFJ tuner.
When I get my little mini
beam up on the tower I will
use the dedicated matching
network. The dedicated
matching network was was
described in the July 1991
article by AE6C. It also
appeared in early 1990s
editions of the ARRL
handbook. My dedicated
matching network will have a
small power screwdriver
motor to turn a variable
capacitor to very high
capacitance (effective short)
or lower capacitance to
cancel out the inductive
reactance present on 80
meters because of the 3/8
wave length of the antenna.
On 40 meters the antenna is
a 3/4 wave wire with a
resistive Z of about 90
|This toroid transformer was pretty simple to build.
I tested it with an Autek RF1 Analyser and a 90 ohm resistive load.
The transformer worked well. This type of transformer can be tapped for other impedances as well. I have two taps on this transformer (the red
wire and the black wire).
The ARRL handbook shows a scheme for 52 ohm to
75 ohm transformer for using 72 ohm cable in your antenna system. All these designs use T-200-2 cores.
I used some white teflon plumbers tape to wrap my torroid above. The red tape is red electrical tape.
These transformers can be used to match 72 ohm coax to 50 ohm coax or for the inverted L as per
the AE6C article. The arrl handbooks and antenna manuals have these types of transformers in
several articles on how to build them.
|A 160/80 meter version of this inverted L would be about 192 ft long. It
operates on the same principal as the 80/40 version. The feedpoint Z is low
and can be matched by a transformer with a capacitor in series at the low
frequency to tune out the inductive reactance that would be present..or an
automatic antenna tuner could be used.
|As per schematic below, I have changed the design a bit. The relay and the original
capacitor changed to a large value variable that can be driven with a slow rpm motor.
At minimum capacitance ranges it should match the antenna on 80 meters (which
would have a slight inductive reactance), On 40 meters the Z of the antenna would
be mostly resistive and about 90 ohms or so. The capacitor at full mesh..about 1200
pf, would be like a dead short on 40. I have to verify this yet in the real world.
|IF you look real
close you can see
the antenna wire
againsts the sky
in the picture.
|June 4-2011..I am currently writing this page and this series of
pages from my old web site (www.earlandrews.com) which I
am closing down. There will be a couple of more pages
concerning small backyard antennas as I write them up. ..73
earl ve3ab LINK HERE BACK TO my index page of
my "FREE" on line magazine
|this page (these pages)..back
yard antennas..is being worked
on (June 4th (ish)) 2011.
I should have these two or
three pages finished in a few
|click here to go to the next
page...>>> Antenna Ideas
for small city lots