T Attenuator
Resistor values for a T pad of given attenuation and impedance.
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The engineering
The Pi pad's dual — series-shunt-series. Identical match and loss; pick whichever suits the layout and the resistor values you can actually buy.
For very low attenuation the T's series values get tiny and tolerance-dominated; Pi behaves better there.
Where this math comes from
Same Bell System image-parameter lineage as the Pi pad — Campbell and Zobel's 1920s toolkit for building networks that stay matched from both directions. T and Pi are the two canonical three-element solutions to the same pair of equations.
Broadcast and telephone plants standardized on decade boxes of these pads long before coax connectors existed.
- 1920George CampbellTwo-port image design formalized.
- 1923Otto ZobelPad synthesis equations in modern form.
See the full timeline of the math behind every calculator →
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