Everyday pi attenuator problems come down to one relationship between impedance (z0), load impedance (zl), source impedance (zs), attenuation (in decibels) and one way. This calculator turns those numbers into resistor 1 (r1), resistor 2 (r2) and impedance factor (k), with the working shown so you can check the result rather than simply trust it.
What Is the Pi Attenuator Calculator?
The pi attenuator calculator turns impedance (z0), load impedance (zl), source impedance (zs), attenuation (in decibels) and one way into resistor 1 (r1), resistor 2 (r2) and impedance factor (k).
It is a quick way to get from the numbers you have to the number you need, without setting up a spreadsheet or reaching for a formula.
How the Pi Attenuator Works
Each result follows from the ones before it, and the calculator shows every step, so a surprising answer can be traced back to the input that caused it.
Round your inputs to the precision you actually know, and keep more precision than that in the intermediate steps.
Getting a Result You Can Trust
Run the calculation twice with slightly different inputs. A sensible calculator moves its output in proportion; a wild change points to a unit or a decimal point problem in what you entered.
Write the inputs down next to the answer. It takes a moment and it is the difference between a number you can explain and one you cannot.
A Worked Example
Working through an example, with impedance (z0) set to 10, load impedance (zl) set to 5, source impedance (zs) set to 2, the calculator returns impedance factor (k) of 100,000, and resistor 1 (r1) of 10.0002, and resistor 2 (r2) of 499,999.99995. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out resistor 1 (r1)?
Enter impedance (z0), load impedance (zl), source impedance (zs), attenuation (in decibels) and one way. The calculator then works through the relationship and reports resistor 1 (r1), resistor 2 (r2) and impedance factor (k).
What does the pi attenuator actually calculate?
It takes impedance (z0), load impedance (zl), source impedance (zs), attenuation (in decibels) and one way and converts them into resistor 1 (r1), resistor 2 (r2) and impedance factor (k) using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter impedance (z0)?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Is the answer exact?
It is as exact as the formula and the inputs allow. The method itself is the standard one for this problem, so the only sources of error are the figures you enter and the precision you ask for.
Why does a small change in one value move the answer so much?
That happens when an output depends on a ratio, because dividing by a small number magnifies any change in it. Check the units first, then check whether the value you entered is in the range the relationship was designed for.