Pi Attenuator Calculator

Your details

Symmetric: source and load have the same impedance (e.g. both 50 ohm). Asymmetric: use different values to match and attenuate simultaneously.
System impedance, typically 50 ohm for RF or 75 ohm for cable TV.
Ω
The signal power reduction you need. Must be at least the minimum attenuation for your chosen impedance ratio.
dB
R1 (shunt input)Excellent match
150.48Ω

Input shunt resistor to ground

R2 (series)37.35Ω
R3 (shunt output)150.48Ω
Minimum attenuation0dB
Input VSWR1
Input return loss99.99dB
Insertion loss6dB
R1 (shunt in)150.48
R2 (series)37.35
R3 (shunt out)150.48

Pi-pad design: 6 dB attenuation with 1.000 VSWR.

  • For a 6 dB symmetric pi-pad at 50 ohm: R1 = R3 = 150.48 ohm, R2 = 37.35 ohm.
  • Input VSWR is 1.000, indicating an excellent impedance match.
  • Input return loss is 100.0 dB. A return loss above 20 dB (VSWR < 1.22) is generally considered acceptable in RF systems.
  • Choose the nearest standard E96 or E24 resistor values and verify the resulting attenuation meets your system tolerance.

Next stepUse 1% tolerance resistors to keep the actual attenuation within 0.5 dB of the design target.

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