Find the total resistance, or Rt, of the circuit. The total resistance depends on the number of resistors in the circuit. If only one resistor exists, the total resistance equals that resistor. If multiple resistors exist, use one of the following formulas depending on whether the resistors are connected in series or in parallel:
Resistors in Series: Rt = R1 + R2 + R3 ... Rn
Resistors in Parallel: Rt =1/(1/R1 + 1/R2 + 1/R3 ...1/Rn)
Find the total inductance, or Lt, of the circuit. The total inductance depends on the number of inductors in the circuit. If only one inductor exists, the total inductance equals that inductor. If multiple inductors exist, use one of the following formulas depending on whether the inductors are connected in series or in parallel:
Inductors in series: Lt = L1 + L2 + L3 ... Ln
Inductors parallel: Lt =1/(1/L1 + 1/L2 + 1/L3 ....1/Ln)
Find the total capacitance, or Ct, of the circuit. The total capacitors depends on the number of capacitors in the circuit. If only one capacitor exist, the total capacitance equals that capacitor. If multiple capacitors exist, then use one of the following formula depending on whether the capacitors are connected in series or in parallel:
Capacitors in series: Ct =1/[1/C1 + 1/C2 + 1/C3 ...1/Cn]
Capacitors parallel: Ct = C1 + C2 + C3 ... Cn
Find the reactance of the inductor, or Xl, using the formula: Xl = (2)(pi)(f)(Lt), where f is frequency and pi is 3.1415. For example, if f is 20 megahertz and Lt from Step 2 is 5 microhenrys, Xl = (2)(3.1415)(20 x 10^6)(5 x 10^-6) = 628.3 ohms.
Find the reactance of the capacitor, or Xc, using the formula: Xc = (2)(pi)(f)(Ct) For example, if f is 20 MHZ and Ct from Step 3 is 2 microfarads, Xl = (2)(3.1415)(20 x 10^6)(2 x 10^-6) = 251.32 ohms.
Find the total reactance using the formula: Xt = Xl - Xc. Using the examples from Steps 4 and 5, Xt = 628.3 - 251.32 = 376.98 ohms.
Calculate impedance using the formula Z = sqrt [Rt^2 + Xt^2]. If you assume Rt from Step 1 is 480 ohms and using Zt of 376.98 ohms from Step 6, you can compute the impedance as follows:
Z = sqrt [480^2 + 376.98^2] = sqrt[230,400 + 142,114] = sqrt[372,514] = 610.34 ohms.