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Monday April 21, 2014

* BALUN Application & Definitions

Application Notes for BUXCOMM BALUN`s

Definitions: BALUN = Symmetrical to Asymmetrical;  (Balanced to Unbalanced)
                 UNUN = Asymmetrical to Asymmetrical; (Unbalanced to Unbalanced)

A lot of antenna designs and open wire, ladder-lines, require symmetrical or balanced
 The voltage potentials and antenna currents need to be symmetrical with
respect to ground, or 180° out of phase.

The advantage of using coaxial cable is best seen when it is routed near tower legs,
masts and conductive objects. Local metal does not influence the RF energy inside
the shielded coaxial cable. The property of having an outer shield at reference ground
is this possible.  Coaxial cables are referred to as asymmetrical or unbalanced.
As we note, a balanced antenna cannot be connected to an unbalanced transmission
line without experiencing large losses, therefore a BALUN is required to provide a
unbalance to balanced match.

Voltage BALUNS:
A voltage BALUN forces voltage potentials equal in amplitude but opposite in sign with
reference to ground is present at its output terminals. A voltage BALUN may
simultaneously act as an impedance transformer, changing the voltage-to-current ratio
of the output with reference to the input.

Current BALUNS:
A current BALUN forces currents equal in amplitude but opposite in sign (180° out of phase)
to flow through its output terminals. A current BALUN may simultaneously act as an
impedance transformer, changing the voltage-to-current ratio of the output with respect
to its input.  The Guanella BALUNS are examples of current BALUNS.

If an antenna is fed at a low-impedance point or current maximum, which most often
happens to be the case, current BALUNS are more effective than voltage BALUNS in
forcing the right currents on the antenna and hence maintaining the desired radiation
pattern.  This is especially important when nearby metallic objects are interfering with
coupling to the antenna.

A current BALUN protects against RF currents flowing on the outer shield of a coaxial
cable or transmission line.

When feeding a a Windom or off-center-fed dipole, it may be necessary to use a line-isolator,
to prevent the antenna RF from inducing currents onto the shield of the coax cable.
 Adding a B2KLISO in the coaxial cable at the output of the transceiver or antenna tuner
often remedies this problem.

An Unun a type of transmission line transformer that has a common line between the
earth side of the input and the ground side of the output terminal.  An Unun is never
a substitute for a BALUN.

For a transformer or BALUN to perform efficiently, the windings should have an
inductive reactance that is 5 to 10 times the impedance of the input, with reference
to the output. A BALUN will not perform at impedance levels greater than its designed
impedance levels. This is the reason a balanced antenna tuner which uses a BALUN
inside the tuner between the transceiver and the tuner input is preferred.   An antenna
tuner with a BALUN between the balanced transmission line inside the tuner, is desired.

BUXCOMM model B1C11
1:1 BALUN: 50 ohms to 50 ohms, or to feed dipoles and similar antennas with 40 to
75 ohm feed points.  The 1:1 current BALUN is also used to feed the input to 450
ohm ladder-line of the G5RV.

BUXCOMM model B1C21
:2 BALUN: 50 to 100 ohms. This Balun is suitable for feeding Vertical Antennas, Quads,
Loop antennas and  Ladder Line antennas.

BUXCOMM model B15C41
1:4 BALUN: 50 to 200 ohms. This Balun is suitable for the coupling 50 ohm coaxial cable
to Windom’s, and off-center-fed antennas.  Sometimes used with folded dipoles that are
fed with 300 ohm twin lead.

BUXCOMM model B15UN41
B1KCUN41, 52 ohm unbalanced input to 200 ohm Unbalanced output
1.5 to 55 MHz, Use to match 50 ohm coax with Vertical Antennas
50 ohm SO239 unbalanced input. (SO239) unbalanced 4:1 (200 ohm) output.
160 meters to 6 meters. 1.5 to 55 MHz;  Multi-Core BALUN, Power Rated at
1500 watts PEP UNUN.

BUXCOMM model B15C51
1:5 BALUN: 50 to 250 ohms; Suitable for coupling 50 ohm coaxial cable to a Windom’s,
when the Windom is more than 50 above ground.  Other applications are trap type
dipole antennas.

BUXCOMM model B15C61
1:6 BALUN: 50 to 300 ohms. This BALUN is suitable for the adjustment to asymmetric
fed dipoles such as Windom’s, G5RV, and zepp antennas. The BALUN is fed directly to
the Windom and similar antennas.  With double-zepp and G5RV antennas and use of
asymmetrical feeder, the BALUN is positioned before entry of the cable into a building.

BUXCOMM model B15C91
1:9 BALUN: 50 to 450 ohms for coupling Asymmetrical to Symmetrical feeders.

BUXCOMM model B15LW91
Long Wire 1:9 UNUN: Similar to above, except; asymmetrical to asymmetrical
Long wire antennas, Ground Plane`s, Verticals, and some "beverage" antennas.

BUXCOMM model B1C101
1:10 BALUN 
The 10 to 1 BALUN may be used with T2FD and Folded dipoles 
where 500 ohm balanced termination resistorstm (BTRreg tm) are employed.  
The 10:1 BALUN is most often used with terminated folded dipoles having 500
ohm balancing termination resistor.
 and certian "beverage" type antennas,..
Other applications for a 10:1 BALUN are: **50/500 Ohms for end fed Beverage antenna, 1-30 MHz. 
Also used with 500 ohm terminated Rhombics, multi-layered, ALE and end-fire antennas.  It is also
used when feeding 450 & 500 ohm ladder-line,

BUXCOMM model B1C121
1:12 BALUN 
The 12 to 1 BALUN most often used with T2FD and Folded dipoles 
where 600 ohm balanced termination resistorstm (BTRreg tm) are employed.  
Also used with 600 ohm terminated Rhombics, multi-layered, ALE and end-fire
antennas.  It is also used when feeding 600 ohm ladder-line,
 and some types of
"beverage" antennas,.. etc
   The 12:1 (MM121 & BTR600) is used in 85% of all
T2FD installations. In a few T2FD applications, a 16 to 1 (BUXCOMM B15C161)
BALUN is employed where an 800 ohm BTR is used.

BUXCOMM model B1C161
1:16 BALUNS are used to feed T2FD folded dipoles, RHOMBICS and similar
antennas which have an 800 ohm termination resistor for balancing power
distribution in the elements.  A 16 to 1 BALUN is also used to feed some types
of ALE and Beverage antennas. 

BUXCOMM model B1K5022: 
This Mobile BALUN/UNUN is designed to put the RF power into your mobile
More than 95% of all HF mobile antennas exhibit a low impedance input,
between 16 and 32 ohms.   The BUXCOMM model
B1K5022, HF mobile UNUN will match
50 ohm coax to mobile antennas having impedance(s) from 14 to 33 ohms.

BUXCOMM High Frequency Vertical antenna Common Mode Isolator is designed to be
installed at the base of your vertical antenna.
Contrary to popular belief that only dipoles need baluns. NOT SO, HF verticals fix'd or mobile
(for mobile version, see model B1K5022), can require BALUN or common-mode isolators.  
The HFVCMI is a BUXCOMM product that fills this purpose to perfection.   It's a current BALUN
with specially fitted output terminals for ease of connecting to the vertical that does not use an
SO239 input. 
In addition, if your match is near  the feedline or coaxial cable impedance, you
could realize gain from your vertical antenna.  P=I2 R. 
When using an HF vertical, we recommend a minimum of 16 radials, bonded together 
and terminating at the base of the antenna... NOTE: I did not say connected TO the base...
I say, terminated at the base.  This is be the point where the coax shield or the ground post
of the BUXCOMM HFVCMI is connected.


Current Baluns vs  Voltage Baluns:

Current baluns, when referenced to ground or other metallic pseudo grounds allow its output terminal voltage,
 float to any level needed to provide equal currents within the antenna feedline or feedpoint conductor. Current baluns
are designed to work with both balanced or unbalanced loads. Current baluns provide a common-mode isolation
between the antenna elements.  Transmission line transformers that are used as baluns, may actually be UNUNs that
also perform well as broadband phase-invertors.

Current baluns isolate or add impedance to unwanted common-mode current paths, reducing  common-mode currents. 
Current baluns are preferred because they perform better than voltage baluns in most antenna applications.

Voltage BALUNS attempt to force equal voltages to the output terminals.  More often than not, the voltage
BALUN will produce a phase shift between the output terminals and reference ground.  If the impedance presented
at each terminal is not exactly the same, feedline and load currents are not equal and/or opposite.  The result is a feedline
or coax shield that will re-radiate, and add to neighborhood TV interference.  In addition, a voltage BALUN does
provide common-mode isolation (CMI).

As stated throughout our BALUN web pages, BUXCOMM manufactures and sell only
"Current BALUNS."  Voltage BALUNS may be special ordered.

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