Attenuators

Related wiki pages; Apparatus, Dummy Load

= 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
 * $$RL_1$$ = leg resistor 1
 * $$RL_2$$ = 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
 * $$RA_1$$ = Arm resistor 1
 * $$RA_2$$ = Arm resistor 2



Approximate resistor values for a single T pad are as follows



How is attenuation measured?
Attenuation is measured in decibels (dB) of relative power. A guide to the attenuation-dB relationship is:

{| style = width:55 border ="1"
 * dB || Attenuation || Power in || Power out
 * 3dB ||0.5 || 100W || 50W
 * 6dB || 0.25 || 100W || 25W
 * 10dB || 0.1 || 100W || 10W
 * 20dB || 0.01 || 100W ||1W
 * 30dB || 0.001 || 100W || 0.1W
 * }
 * 20dB || 0.01 || 100W ||1W
 * 30dB || 0.001 || 100W || 0.1W
 * }
 * 30dB || 0.001 || 100W || 0.1W
 * }
 * }