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.

Attenuator Circuits

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 calculatorsfrom NU9N

• Attenuator calculator 1.2 Attenuator calculator software.

• Pi calculator

• Pi and T pad calculator

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
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

Electronic Theory
Physical quantities	Current * Gain * Impedance * Power * Q of a circuit * Radiated Power Measurement * Reactance* Resistivity * Resonance * Voltage
Components	Baluns * Bipolar-Junction Transistors * Capacitors * Diodes * Inductors* Lasers * Microphones * Resistors * Transformers * Wire
Circuits	Attenuators * Digital Signal Processing (DSP) * Dummy load * Filters * LC filters * Power Supply Design * Rectifier Circuits
Design	Amplifier Design * Oscillator Design
Electromagnetic Waves	Relative power (Decibels) * Harmonics * Interference and BPL