Pi Attenuator
Resistor values for a Pi pad of given attenuation and impedance.
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The engineering
Three resistors that attenuate while looking like Z₀ from both ends — the matched way to knock a signal down. The power row is the reminder that a 10 dB pad eats 90% of what enters it; size the resistors for the job.
Pi vs T is layout preference at these values; both are exact.
Where this math comes from
Matched pads come from telephone-network theory — Otto Zobel and George Campbell's image-parameter school at Bell (1920s), which treated every network as something that must look right from both directions. Attenuators were the calibrated 'loss' you inserted on purpose.
The same arithmetic, in coaxial form with exotic resistor films, is what a $2,000 precision step attenuator still is inside.
- 1920George Campbell / Bell SystemImage-parameter network design matures.
- 1923Otto ZobelSystematic matched-network (pad/filter) synthesis.
See the full timeline of the math behind every calculator →
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