an All Band HF Air Core
1:1 Choke Balun
THE "UGLY BALUN"
A balun's purpose is to allow connecting a BALanced
load (e.g., a dipole or driven element) to an UNbalanced
line such as coax which is not balanced, thus the name, Balun. The
1:1 choke "balun" is not actually a balun. It's function is to
help eliminate rf currents from flowing on the outside of coaxial cable using
the principle of choke action.
In transmitting antennas, this is accomplished by presenting a high impedance
(resistance), to RF currents flowing outside the coax shield. This forces
currents in each side of a driven elements to be equal. This is especially
important in beam antennas because it prevents distortion of the beam's pattern
caused by unequal currents in the driver(s). In a simple dipole, the balun
(choke), assures that
the dipole, and not the feed line, is doing the radiating!
When you connect center fed antennas, like dipoles, V's, triangles, yagis,
rhombics, loops and so on, to coaxial cable, unless care is taken, it is not
difficult to end up with feeder radiation. Not only
can the loss in power be quite significant, but the radiation characteristics of
the antenna system will also be seriously compromised.
In laymen's terms, it won't be what you are expecting from the pattern of your
As the feedline becomes part of the antenna, currents can flow from the line
into the mains and on TV cables, metal masts and yagi booms, causing a variety
of EMI problems that can be very difficult to trace. Frequently these
problems are simply due to unbalance - and the solution is the humble air choke.
If an antenna system is fed at center with a parallel conductor line (provided
that correct installation procedures are followed) balance will be maintained,
USING A BALUN, with currents in equal and opposite phase canceling each other
When the connection is
to a coaxial cable, WITHOUT A BALUN, this cannot occur because currents flowing
inside the cable from the connection to the inner conductor are separated from
those flowing on the outside from the connection to the shield, and the result
is unbalance causing feeder radiation. However, if the two electrical circuit
elements (antenna and coaxial cable) are coupled using a balan, balance will be
Enter.....The Ugly Balun!.....
50 ohm Balun
An Inexpensive, High-Performance,
"Building a no-grief 1.8MHz to 30MHz 50ohm-balun is easy.!"
costly ferrite-cores are needed, just a short length of 3 to 5 inch size plastic
pipe, about 25 feet of 50ohm coax plus some nylon cable ties.
Solid-dielectric coax is best for this application because foam-dielectric has a
tendency to allow a change in the conductor to conductor spacing over a period
of time if it is bent into a tight circle. This can eventually result in voltage
breakdown of the internal insulation.
The required length of the plastic pipe depends on the diameter and length of
the coax used and the diameter of the pipe. For RG-213/U coax, about one foot of
5 inch size pipe is needed for a 1.8MHz to 30MHz balun. For 3.5MHz to 30MHz
coverage, about 18 to 21 feet of coax is needed. This length of coax is also
adequate for most applications on 1.8MHz.
18 to 21 feet should cover all of 160 through 10
number of turns is not critical because the inductance depends more on the
length of the wire (coax) than on the number of turns, which will vary depending
on the diameter of the plastic pipe that is used.
The coax is single-layer close-wound
on the plastic pipe.
The first and last turns of the coax
are secured to the plastic pipe with nylon cable ties passed through small holes
drilled in the plastic pipe.
coil winding must not be placed against a conductor.
The name of this simple but
effective device is a choke-balun.
people build choke-baluns, without a plastic coil-form, by scramble-winding the
coax into a coil and taping it together. The problem with scramble-winding is
that the first and last turns of the coax may touch each other. This creates two
complications. The distributed-capacitance of the balun is increased and the
RF-lossy vinyl jacket of the coax is subjected to a high RF-voltage. The
single-layer winding on the plastic coil-form construction method solves these
problems since it divides the RF-voltage and capacitance evenly across each turn
of the balun"....AG6K
Credit for this article goes to AG6K, Rick Measures and was edited from a
Pre-copy version of another article titled "A BALANCED - BALANCED ANTENNA
TUNER" published in QST,February, 1990.
"Ugly Balun" photos, ideas and
installations sent in by users!
examples in the pictures below using cable ties on PVC pipe forms which work
well also. Your choice!
(Imagine the coil form is removed). Pictures are showing how to secure the coils
together. Do not let the first and last coils touch!
Picture above courtesy of VE7AVV
Picture above courtesy of
KC2NXV shows using 2 pvc couplers joined and glued using about 2 inches of 4
inch PVC pipe, so the couplers would adhere and be stronger.
More "Ugly Balun" ideas from
DAVE THOMAS, M3RUH BELOW:
The Dave Thomas, MW3RUH BOTTLE SPECIAL!
Dave uses a plastic drink bottle as a form. He installs an
S0-239 in the bottle cap and antenna connectors on the other end!
NICE TIP DAVE!
Photos courtesy Bill, KI4PCB,
using 4 " PVC FORM
Notice the screw terminal block used for connections
KI4PCB "Ugly Balun" on the air!
The N7ATA "Ugly Balun in Real Life"...thanks
Courtesy of G4APL (see info below)
Courtesy of G4APL (See info below)
Courtesy of G4APL.
(Air choke used on Mosley
Mustang Mark3 3 element 10,15, 20 metre trapped Yagi)
G4APL Ugly Choke Balun inline with the GB7CIP Pactor
Trapped HF Ground Plane
Ugly Choke Balun by G4APL
Paul, G4APL, has brought
together some excellent examples on how to construct and build Choke Balun in
the pictures above and the information below to share with us:
Paul decided to build two or
three of them, depending on what material could be found in the shed.
The idea was to add a balun
to the HF beam, a Mosley Mustang Mark3 3 element 10,15, 20 metre trapped yagi.
This is fed with co-ax and has the Mosley earth strapped at the feed point. The
beam has been adjusted for the low end of the HF (High Frequency) bands.
Paul had used a commercial
balun in the 1970’s before and burnt this one out. It was supposed to be rated
to 1 kilowatt pep. (peak envelope power).
Using the information
material from the instructions for the "Ugly Balun" above, it was time
to see what was in the shed.
A short length of 4 inch
drain pipe was located that was left over from the 90 foot of drain pipe laid
underground that carries the RF cables. Also found a 2 inch piece of down pipe.
Materials: HF Beam Balun
12 inches length of 4inch
diameter PVC drain pile
18 foot of RG58
two suitable cable plugs
Having got all the required
tools out, it Paul and hour to build the Ugly Choke Balun as pictured
The HF Balun is attached
vertically to the Stub Mast at the Mosley Mustang Mark3 beam
Paul was very surprised with
the results. Testing the aerial and Balun with 250 Watts the standing wave was
Never seen this beam produce
these results before!
14.005MHz to 14.150MHz 1.1:1
21.005MHz to 21.300 1.1:1
28.005MHz – 28:400MHz 1.1:1
Now to do some dxing and see how the
Hope the above
is of use to you.........73 Paul G4APL
More from ZL1ALZ, JOHN from New Zealand!
"Ugly Balun" construction used on a 40 meter vertical!
Closeup of the ZL1ALZ "Ugly Balun"
The VE2ITZ Balun with Sloper Antenna!
Never had such an easy time at tuning the sloper
antennas with the "Ugly Balun"!
the way; the balun consists of 20 feet of coax wound around a 2 and a half
inch diameter plastic bottle. I then proceeded to put gaffer tape to hold it in
Cheers and 73 de VE2ITZ in Montreal, Canada