Transformers in Communications Circuits

Chapter Transformers in Communications Circuits

Complete Electronics Self Teaching Guide with Projects
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Complete Electronics Self Teaching Guide with Projects

  • TRANSFORMERS IN COMMUNICATIONS CIRCUITS447TRANSFORMERS IN COMMUNICATIONS CIRCUITS14  In communications circuits, an input signal is often received via a long interconnecting wire (usually called a line) that normally has an impedance of 600 ohms. A typical example is a telephone line between two cities.QUESTIONCommunications equipment works best when connected to a load that has the same impedance as the output of the equipment. What output impedance should commu-nications equipment have? ANSWER600 ohms output impedance, to be connected to a 600-ohm line15  Because most electronic equipment does not have a 600-ohm output impedance, a trans-former is often used to connect such equipment to a line. Often, the transformer is built into the equipment for convenience. The transformer is used to “match” the equipment to the line, as shown in Figure 10.10.FIGURE 10.10Equip-mentLineTo work correctly, the output of the transformer secondary coil should have a 600-ohm impedance to match the line. The output impedance of the transformer (measured at the secondary winding) is governed by two things. One of these is the output imped-ance of the equipment.QUESTIONWhat would you expect the other governing factor to be? Book Authorc10V106/14/2012 9:01 AM c10.indd 4476/14/2012 9:01:50 AM