Baluns and ununs are fun construction projects.They are electrically simple, and easy to fabricate with hand tools. I have enjoyed building many baluns; here are pictures of some I have built recently.
Building And Using Baluns And Ununs Pdf
His talk covers some of the history of transmission line transformers leading to the development of baluns, ununs and choke baluns as well as definitions and theory. Some discussion on chosing the right balun included ideas on measuring common mode current, consequences of high- vs. low-power wiring, misconceptions about ratios, use of ladder line with baluns and grounding. Finally Dave walked us through a number of examples based on different antenna configurations including some being used by WCARES members.
Baluns and ununs are essential in RF signal chains for many applications. RF balun designs are most commonly associated with core-and-wire transformers, but can also be realized through coaxial and coupled stripline technologies. The behavior of baluns and ununs was introduced in Part 1 of this series, where we established that both these devices are designed for impedance matching purposes. The major difference between them is that baluns are designed to match impedances between balanced and unbalanced circuits, whereas ununs provide impedance matching between two unbalanced circuits.
Part 1 of our Demystifying RF Transformers series discusses the basic theory and applications of RF transformers. This article aims to provide a deeper investigation into baluns and ununs with the main focus on baluns due to their greater prevalence in real-world applications.
The most common use for baluns is when a single-ended power amplifier is used to drive a balanced load. Examples include dipole antennas or single-ended antennas such as whips, which are needed to feed an additional front-end amplifier (see figure 1). In the past, baluns were also widely used in the CATV industry, for example when matching between a 300Ω dipole antenna for broadcast TV with a 75Ω coaxial cable. With the development of RF Integrated Circuits (RFICs), baluns are now also widely used to improve noise immunity and common mode rejection. The growth in 5G applications has also led to tremendous demand for small, wideband baluns to interface with highly integrated radio transceivers using differential inputs and outputs.
Broadband balun transformers are also constructed with various impedance transformations using several transmission lines in series and parallel arrangements. In this case, the impedance transformation is 1:n2, where n is the number of series-parallel transmission lines. Quarter-wave and half-wave transmission line balun transformers are also possible, although these types of baluns are best suited to applications with a narrow operating frequency range.
Balun production can also involve the use of planar metal structures with technologies such as LTCC and MMIC. This choice of design and fabrication is often proprietary. Generally, the main benefit of these designs is the small footprint that can be readily integrated into a microwave assembly. Unlike other baluns, LTCC- and MMIC-based baluns are produced using high-precision assembly machines and seminconductor manfacturing methods that yield much higher repeatability.
For use with RF antennas, baluns are needed where a balanced antenna such as a dipole is used. The most convenient form of feeder to use is coaxial cable as this can be routed far more conveniently along antenna towers, or poles, along the ground and through buildings, etc without the need to worry about affecting the coax cable performance.
Prevent radiation / pickup from coax outer conductor: If a balanced antenna is used and fed directly using coaxial feeder, then it is found that the outer or shield of the coax can radiate and pick-up radio frequency signals. For receiving, this can mean that interference from electrical apparatus, etc within the home, building, or just close to the feeder can be picked up. For transmitting, it can mean that the feeder will radiate signal which could cause interference and result in feeder loss.
Transmission line or choke baluns can be considered as simple forms of transmission line transformers. This type is sometimes called a current balun, since it ensures equal current on both sides of its output, but not necessarily equal voltage. These are normally called ununs, because they go from unbalanced to unbalanced or un-un. Baluns are balanced to unbalanced or bal-un.
A more subtle type results when the transformer type (magnetic coupling) is combined with the transmission line type (electro-magnetic coupling). Most typically the same kind of transmission line wires are used for the windings as carry the signal from the radio to the antenna, although these baluns can be made using any type of wire. The resulting devices have very wideband operation.[3] Transmission line transformers commonly use small ferrite cores in toroidal rings or two-hole, binocular, shapes.
Baseband video uses frequencies up to several megahertz. A balun can be used to couple video signals to twisted-pair cables instead of using coaxial cable. Many security cameras now have both a balanced unshielded twisted pair (UTP) output and an unbalanced coaxial one via an internal balun. A balun is also used on the video recorder end to convert back from the 100 Ω balanced to 75 Ω unbalanced. A balun of this type has a BNC connector with two screw terminals.VGA/DVI baluns are baluns with electronic circuitry used to connect VGA/DVI sources (laptop, DVD, etc.) to VGA/DVI display devices over long runs of CAT-5/CAT-6 cable. Runs over 130 m (400 ft) may lose quality because of attenuation and variations in the arrival time of each signal. A skew control and special low skew or skew free cable is used for runs over 130 m (400 ft).[citation needed] 2ff7e9595c
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