Adding a Custom Lossy Line

AN-SOF provides parameters for modeling the losses of more than 160 types of transmission lines. These parameters have been obtained by adjusting the loss model to the attenuation curves published by manufacturers. In case a particular type of cable is not listed or if the manufacturer has updated the parameters, a custom transmission line can be created using the following procedure:

1. Open the Transmission Lines window by going to the main menu > Draw > Transmission Lines (Ctrl + L) or follow the procedure in Connecting Transmission Lines to open this window by selecting a wire.

2. Select a row from the table by clicking on the row number (under the first column labeled No.).

3. In the panel on the right, double-click the Custom line low loss model option.

4. All manufacturers publish the nominal characteristic impedance, Z0, and the velocity factor, VF. Enter these values as well as the length of the line. If you enter “0” in the length cell, the linear distance between the ends of the cable will be calculated.

5. Manufacturers also publish an attenuation table as a function of frequency. Here is an example for the Belden 8237 cable, type RG-8/U:

6. In the cells corresponding to Att. 1, Freq. 1, Att. 2, and Freq. 2, enter the values from the attenuation table so that the simulation frequency range is included between Freq. 1 and Freq. 2. For example, if you are running a calculation between 150 and 170 MHz, enter Att. 1 = 1.9 dB/100 ft, Freq. 1 = 100 MHz, Att. 2 = 2.8 dB/100 ft, Freq. 2 = 200 MHz, as indicated in the table for the Belden 8237 cable, Fig. 1.

Be careful with the units of attenuation and frequency, as they will be displayed in the units chosen in the Preferences window. Go to main menu > Tools > Preferences > Units tab to change the units for frequency and length.