The change is caused by the internal inductance (inductance within the conductors), which becomes a larger percentage of the total inductance at low frequencies. This shows the significant amount by which the velocity factor changes at lower frequencies for the same two RG-58 lines. K2 is associated with the dielectric loss which varies directly with frequency.) K1 is associated with the "skin effect" or "high frequency" resistance of the conductors which varies in proportion to the square root of frequency. (K0 is associated with the DC resistance of the conductors which is a constant for any given line type. The fact that the matched line loss differs is reflected in the fact that the K0/K1/K2 loss coefficients have different values. The screen capture above (reduced size) shows the matched line loss comparison for two different types of Belden RG-58 coax. You can also compare one line with another by clicking the "Compare" button to freeze one trace and then selecting a different line type from the drop-down list. You can experiment with changes to the line parameters (Nominal Zo, Nominal VF, loss coefficients K0/K1/K2) to see how the plots change at various frequencies. TLDetails includes a plot function that allows you to plot the matched line loss, the true velocity factor, or the true characteristic impedance magnitude, over a frequency range of either 0.1 to 100 MHz or 1 to 1000 MHz. All program inputs may be changed directly or you can use spin buttons to make the changes.
You can modify the specs to see how small changes affect the results or to specify custom lines. It includes built-in specifications for approximately 100 different line types. This utility program shows the impedance and reflection coefficient parameters (SWR, reflection coefficient magnitude Rho, or Return Loss RL in dB) at both ends of a transmission line and the details of power loss in the line.
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