Pi Attenuator Calculator
Calculate resistor values for a Pi (π) attenuator circuit. Pi attenuators reduce signal power while maintaining impedance matching.
How to Use This Calculator
- Enter the characteristic impedance (typically 50Ω for RF, 75Ω for video).
- Enter the desired attenuation in decibels (dB).
- The calculator displays the required resistor values: R1 (shunt) and R2 (series).
- Use two R1 resistors (one at input, one at output) and one R2 resistor (series).
Pi Attenuator Formula
Resistor values are calculated from impedance and attenuation:
R1 = Z₀ × ((K + 1) / (K - 1))
R2 = Z₀ × ((K² - 1) / (2K))
Example: 50Ω impedance, 10dB attenuation: K = 10^(10/20) = 3.162. R1 = 50 × (4.162/2.162) = 96.2Ω. R2 = 50 × (9/6.324) = 71.1Ω. Use two 96.2Ω resistors (shunt) and one 71.1Ω resistor (series).
Full Description
Pi attenuators are passive circuits used to reduce signal power while maintaining impedance matching. They're called "Pi" because the circuit topology resembles the Greek letter π, with two shunt resistors (R1) at the input and output, and one series resistor (R2) connecting them. Pi attenuators are widely used in RF circuits, test equipment, and communication systems.
The key advantage of Pi attenuators is that they maintain the same input and output impedance (typically 50Ω or 75Ω), preventing reflections and ensuring proper impedance matching. The attenuation is determined by the ratio of resistor values, which are calculated from the desired attenuation in decibels and the characteristic impedance. Pi attenuators are bidirectional—they work the same in both directions.
This calculator helps you determine Pi attenuator resistor values. Enter the characteristic impedance and desired attenuation, and it calculates R1 (shunt) and R2 (series) values. Use it when designing RF circuits, building test equipment, adjusting signal levels, or understanding how attenuators work. Pi attenuators are essential components in RF and communication systems.
Frequently Asked Questions
What is a Pi attenuator?
A Pi (π) attenuator is a passive circuit that reduces signal power while maintaining impedance matching. It's called "Pi" because the circuit looks like the Greek letter π, with two shunt resistors (R1) and one series resistor (R2).
When do I use a Pi attenuator?
Use Pi attenuators to: reduce signal power, match impedances, protect sensitive circuits from high-power signals, or adjust signal levels in RF systems. They're common in RF circuits, test equipment, and communication systems.
How do I calculate Pi attenuator resistors?
R1 = Z₀ × ((K + 1) / (K - 1)), R2 = Z₀ × ((K² - 1) / (2K)), where K = 10^(Attenuation/20). Two R1 resistors (shunt) and one R2 resistor (series). The calculator does this automatically.
What's the difference between Pi and T attenuators?
Pi attenuator: Two shunt resistors (R1) at input/output, one series resistor (R2) in between. T attenuator: Two series resistors (R1) at input/output, one shunt resistor (R2) in the middle. Both provide the same attenuation, but component values differ. Choose based on circuit topology.