Each of them is different electrically. A voltage balun is a transformer, mostly with a primary and one or more secondary windings on a ferrite core.
A voltage balun is one whose output voltage is equal and opposite, balanced with respect to ground. In order to attain true balance, the baluns load must be symmetric with respect to ground. Voltage baluns are commonly used and can be easily constructed. Transmission line voltage balun is constructed solely from the transmission line and requires cores.
This balun is used only over a narrow range of frequencies. A current balun is balanced with respect to ground, its output currents are equal and opposite. The exception of the current balun, current baluns are more expensive to construct than the voltage baluns so they are not widely used as a voltage balun. Current baluns could be made with RF transformers on ferrite cores or with lengths of the transmission line. The common-mode field can be seen by current balun.
An unbalanced transmission line coaxial cable connected to a dipole antenna. In Figure 1, a coaxial cable is connected to a dipole antenna. For a dipole antenna to operate properly, the currents on both arms of the dipole should be equal in magnitude. When a coaxial cable is connected directly to a dipole antenna however, the currents will not neccessarily be equal. To see this, note that the current along a transmission line should be of equal magnitude on the inner and outer conductors, as is typically the case.
The result can be ringing or ghosting, not to mention unwanted radiation of the signal from the coaxial cable which is now working as part of the load. The solution to these issues is to use a small transformer to convert from an unbalanced to a balanced signal, and vice-versa.
This transformer is known as a balun, and they are in operation in anything from telephone lines to transmitters. Baluns are used both to sort out the flow of AC signals and make the necessary impedance transformation between coaxial cable, which has a low impedance, and balanced loads, which have higher impedances. With a balun, I can now send AC signals of any kind over a pair of wires and make the necessary transformations at either end to effect a clean transfer of AC signals.
At RF frequencies, the use of a balun is necessary for correct function of transmitters and antennas. If not, unwanted current flow and mismatches can increase interference to adjacent electronic equipment through stray coupling into power lines, audio cables, and antennas.
Need help? Sign In. Brands Hellermann Tyton Signamax Inc. Brands Platinum Tools, Inc. Fire Protection. Safety Equipment. Fiber Optic. It can disrupt data mode transmissions when RF gets onto the interface between the transmitter and the computer causing the system to fail. If analogue audio transmissions are being used then it can get onto the audio input lines and cause strange feedback effects. The solution to issues like this can be to use a balun at the balanced to unbalanced transition.
Even if the issue is not cured, it is most likely to improve the situation. The basic concept of a balun is normally to use a transformer. Although there are many different types of balun, the basic transformer type is a good place to start to illustrate the basic operation. The concept of a balun is based around a transformer, and its main function as a balun is to isolate the direct connection between the balanced antenna or feeder and the unbalanced coaxial feeder.
In this way, the earth connection for the unbalanced cable is not directly connected to the balanced system, and it remains balanced. All transformers have a limited bandwidth, so the bandwidth of the balun must be designed to be greater than that of the antenna or other system with which it will be used.
Concept of an antenna balun The most obvious method of creating a balun is to create a transformer with two windings - one side is grounded, and the other side has differential outputs. It is possible to ground a centre tap on the balun if needed, but for antenna systems this is not normally done. It is also worth noting that the balun is bi-directional, there is no input or output as such, only balanced and unbalanced sets of terminations.
There are two main classes of baluns that can be realised: Current balun: the current balun forces equal current through the two sides of a balanced load.
The current balun is effectively a simple transmission line such as a bifilar winding or coaxial cable wound on a ferrite core. Voltage balun: The voltage balun forces equal voltage across the two sides of a balanced load.
Voltage baluns are a little more complicated than current baluns and prove to be very inefficient in preventing the coaxial cable shield as well as open ladder line to carry common mode currents and radiate energy.
Accordingly voltage baluns are not used for most antenna applications. Although the essence of many baluns is a transformer, there are several different types of balun that can be used.
Some employ different circuit techniques, while others use different concepts. However all form the basic function of changing from a balanced to unbalanced system. Classical transformer balun: The traditional approach for a balun is to use a transformer. This consists of two electrically separate windings, normally wound on a core - typically a toroidal ferrite core.
Having two separate windings in this fashion means that the two circuits are electrically isolated which can have advantages for some applications.
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