Building And Using Baluns And Ununs Pdf
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In the past, baluns were commonly used to interface antennas with long coaxial cables. The baluns used in this case were designed to match the impedances of the coaxial cable, the antenna and the balun. With the development of integrated circuits, baluns have been used for other purposes. For example, they can be used to couple RF signals to coaxial cables with center conductors that are unbalanced (see figure 2), allowing a balanced signal to be transmitted over an unbalanced channel. This is useful when a balanced signal needs to be transmitted over an unbalanced bus, for example in a home networking cable.
Older baluns could be used to convert between balanced and unbalanced signals. An example of this is in a television set. The antenna, tuner, IF amplifier and video amplifier are connected through a balun, which is configured to balance the RF signal. In order to prevent coupling between the tuner and the video amplifier, a balun is used to split the IF signal. The video amplifier is then connected to the tuner without a balun, so it is unbalanced. There are also baluns designed to convert between balanced and unbalanced signals between an RF amplifier and an RF receiver. In this case, the balun will have a higher impedance than the RF amplifier and a lower than the RF receiver. Both these designs use a differential pair of transmission lines.
The design of the balun also affects the efficiency of the device. A poor design can make the transfer of power from the balanced to the unbalanced side extremely inefficient. In this case, the total power transferred between the two circuits is lower than the power taken by the balun. This makes the balun very inefficient. On the other hand, the loss of power in a good balun has little effect on the overall power transfer. In either case, the total power transferred between the balanced and unbalanced circuits is maintained. The transfer of power between the balanced and unbalanced circuits is independent of the impedances between them and the balun. This is why a good balun is essential for RF transmission lines. The loss from the balun is compensated by the use of a proper transmission line for the same length. It is these design factors that make a good balun so useful in RF signal chains.
After this introduction to baluns and ununs, we will move on to make the design of baluns and ununs more practical by providing some useful design guidelines, and a few measured examples. More advanced design examples will be presented at the end of this series.
A balun is a simple core-and-wire transformer that is used to transform the impedance of an unbalanced feeder circuit into the impedance of a balanced load. The balun is a key component in a balanced feeder circuit. Baluns do not work in the reverse; a balun cannot transform the impedance of a balanced load into the unbalanced impedance of a feeder circuit. Baluns may be used in the receive path of an RF radio, as well as in the transmit path of a radio. They may also be used in the feed path of a coaxial cable. 827ec27edc