Use this tool to calculate resistor values for a Pi attenuator pad.
These attenuators are used in Radio Frequency (RF) circuits.
Enter the desired value of attenuation and the characteristic impedance The default value is 50 ohm. However it can be changed to any arbitrary value – for instance 75 ohm.
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Calculator
Formula
R1 = Zo [10dB/20 + 1] / [10dB/20 – 1]
R2 = Zo/2 [10dB/10 – 1] / [10dB/20]
where R1 are the shunt resistor values and R2 is the series resistor.
To build this attenuator you will need
- two shunt resistors – one at the input and the other at the output
- one series resistor
Background
What is the Pi Attenuator Calculator?
The Pi attenuator calculator is a useful tool for engineers and technicians working in the field of Radio Frequency Electronics and Telecommunications.
An attenuator is a device used to reduce the amplitude or power of a signal without distorting its waveform. Attenuators are used for example, in receivers to reduce the signal amplitude at various stages in the receiver chain.
The Pi attenuator is a type of attenuator that consists of three resistors connected in the shape of a π.
This specific calculator allows users to easily determine the values of the three resistors needed to achieve a desired attenuation level. By inputting the desired attenuation and the impedance values of the source and load, the calculator instantly calculates the resistor values required.
The use of this calculator saves time and effort for engineers and technologists who rely on accurate calculations in their work and don’t want to compute resistor values manually.
With the Pi attenuator calculator, engineers and technicians can design and implement attenuators that meet specific requirements, ensuring optimal signal transmission in various electronic systems and applications.
How to build a Pi attenuator
At low frequencies (no more than a few MHz) it is possible to build this attenuator with a breadboard and resistors.
At higher frequencies, it becomes necessary to use a PCB with surface mount resistors. The kit shown in the picture below can be used to construct an attenuator with 0805 size resistors.
SMA connectors are to be soldered to the two ends. The attenuator is symmetric and it doesn’t matter which end is the input or output.
Resistor values R1, R2 and R3 can be found using the calculator on this page. R1 and R3, the shunt resistors are equal in value. The orientation of R1 and R3 is such that the currents are balanced.
Related Tools
Pi Attenuator Table
Below is a table of resistor values for attenuation values from 1dB to 50 dB. The impedance value is 50 ohm.
| Attenuation (dB) | R1 (Ohm) | R2 (Ohm) |
| 1 | 869.5 | 5.8 |
| 2 | 436.2 | 11.6 |
| 3 | 292.4 | 17.6 |
| 4 | 221.0 | 23.8 |
| 5 | 178.5 | 30.4 |
| 6 | 150.5 | 37.4 |
| 7 | 130.7 | 44.8 |
| 8 | 116.1 | 52.8 |
| 9 | 105.0 | 61.6 |
| 10 | 96.2 | 71.2 |
| 11 | 89.2 | 81.7 |
| 12 | 83.5 | 93.2 |
| 13 | 78.8 | 106.1 |
| 14 | 74.9 | 120.3 |
| 15 | 71.6 | 136.1 |
| 16 | 68.8 | 153.8 |
| 17 | 66.4 | 173.5 |
| 18 | 64.4 | 195.4 |
| 19 | 62.6 | 220.0 |
| 20 | 61.1 | 247.5 |
| 21 | 59.8 | 278.3 |
| 22 | 58.6 | 312.7 |
| 23 | 57.6 | 351.4 |
| 24 | 56.7 | 394.6 |
| 25 | 56.0 | 443.2 |
| 26 | 55.3 | 497.6 |
| 27 | 54.7 | 558.6 |
| 28 | 54.1 | 627.0 |
| 29 | 53.7 | 703.7 |
| 30 | 53.3 | 789.8 |
| 31 | 52.9 | 886.3 |
| 32 | 52.6 | 994.6 |
| 33 | 52.3 | 1116.1 |
| 34 | 52.0 | 1252.5 |
| 35 | 51.8 | 1405.4 |
| 36 | 51.6 | 1577.0 |
| 37 | 51.4 | 1769.5 |
| 38 | 51.3 | 1985.5 |
| 39 | 51.1 | 2227.8 |
| 40 | 51.0 | 2499.8 |
| 41 | 50.9 | 2804.8 |
| 42 | 50.8 | 3147.1 |
| 43 | 50.7 | 3531.2 |
| 44 | 50.6 | 3962.1 |
| 45 | 50.6 | 4445.6 |
| 46 | 50.5 | 4988.0 |
| 47 | 50.4 | 5596.7 |
| 48 | 50.4 | 6279.6 |
| 49 | 50.4 | 7045.9 |
| 50 | 50.3 | 7905.6 |