What is an attenuator?
An attenuator is a resistive device that reduces the amplitude of a signal without adding distortion to it. The amplitude of a radio signal is the power, so an attenuator is used to reduce the power of a transmission.
When would we use one?
- When making transmission measurements using highly sensitive equipment. The attenuator reduces power to protect the measuring equipment.
- To produce low power for QRP transmissions. many modern HF rigs have a minimum power out of around 5 Watts. QRP operators usually use powers well below this.
The pi circuit
In the circuit below, known as a pi pad;
- RA = Arm resistor
- <math>RL_1</math> = leg resistor 1
- <math>RL_2</math> = leg resistor 2
Approximate resistor values for a single pi pad are as follows
The T circuit
In the circuit below, known as a T pad;
- RL = Leg resistor
- <math>RA_1</math> = Arm resistor 1
- <math>RA_2</math> = Arm resistor 2
Approximate resistor values for a single T pad are as follows
The H circuit
Also known as the H pad or I circuit(I pad)
The O circuit
Also known as the O pad.
Online attenuator calculators
- T and H pad calculators from NU9N
- Attenuator calculator 1.2 Attenuator calculator software.
How is attenuation measured?
Attenuation is measured in decibels (dB) of relative power. A guide to the attenuation-dB relationship is:
|dB||Attenuation||Power in||Power out|