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RF Electronics Chapter 2: Computer Simulation Page 11 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Hz or as convenient values, such as µH, nH, nF, pF, MHz or GHz. If the base values are used, then equations such as equations 2.1 and 2.2 can be used. If convenient units are used, then the appropriate multipliers need to be included in the equations to result in say pF for the capacitance, when a frequency in MHz is entered. When convenient units are used, all the graphs will have the x-axis in the convenient (MHz) units. If the same equations or the same variables are shared in more than one circuit, it is better to locate the equations in the Global Definitions window shown in the left pane of figure 2.7. Those equations are then available to all circuits. In figure 2.7, the thickness of the lines can be changed by selecting Options Environment Options Schematics/Diagrams and setting Symbol Thickness to 10 then setting OK. It is also possible to have equations using the output parameters of a circuit. This is demonstrated in example 5, Bandpass T Matching Network, of this chapter. Optimisation Example 2.2: Diplexer It is required to design a Diplexer to permit VHF and UHF TV signals to be received by separate antennae and then combined, for use by a TV. In Australia the VHF TV frequencies range from 46 MHz to 230 MHz and the UHF TV frequencies range from 527 MHz to 820 MHz. Similar frequency ranges are used in other countries. For this example, 250 MHz is used as the boundary between VHF and UHF. As a result, S 21 (low- pass transfer function) is to be greater than -3 dB for frequencies below 250 MHz and S 31 (high-pass transfer function) is to be greater than -3 dB for frequencies above 250 MHz. A low pass filter with a cut off frequency of 250 MHz, as shown in figure 2.6 is used for the VHF signals and a high-pass filter with a cut off frequency of 250 MHz, is used for the UHF signals. These two filters are then connected as shown in figure 2.9. The same circuit can be used as a splitter, to separate FM radio and VHF TV signals from UHF TV signals. A diplexer consists of a low-pass filter selecting the low frequency components and a high-pass filter selecting the high frequency components. Figure 2.8. High-pass filter. RF Electronics: Design and Simulation 11 www.cadence.com/go/awr