RF Ohm's Law Calculator
Relating Power (P), Voltage (V), Current (I), and Impedance (Z).
Default fixed Z mode for RF Systems.
RF Ohm's Law Cheat Sheet
Engineering Principles: The Ohm's Law Wheel (RF)
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points. In RF engineering, we primarily deal with Power (P) and Characteristic Impedance (Z0) rather than steady-state resistance.
Rate of energy transfer. In 50Ω systems, Power is the primary metric.
EMF required to drive current through impedance.
Charge flow rate relative to power and impedance.
Technical Notes
- •These formulas assume a purely resistive impedance (Real part only). For complex impedance (R + jX), magnitude and phase must be considered.
- •RF power is typically measured in 50Ω systems. A 100W signal corresponds to ~70.7V RMS.
Frequently Asked Questions
Why use Z (Impedance) instead of R (Resistance)?
Resistance deals only with DC signals. Impedance (Z) includes both Resistance (R) and Reactance (X). In RF systems, reactance causes phase shifts and signal reflection, so Ohm's Law must account for total Impedance.
What happens if I put 100W into a 50Ω load?
Using P = V²/R, we solve for V = √(P×R). So V = √(100×50) = √5000 ≈ 70.7 Volts RMS. The peak voltage would be 1.414 × 70.7 ≈ 100 Volts.
Is RF Ohm's Law different from DC Ohm's Law?
The fundamental physics (V=IR) remains the same. However, in RF, variables become frequency-dependent (due to skin effect and capacitive/inductive reactance), and we typically work with Power/Impedance pairs rather than Voltage/Current pairs.