Passive Audio Attenuators
Once in common use in radio, the passive attenuator is used less frequently today because of active circuitry and bridging impedances instead of matched impedances.
The basic attenuator is a T pad, which provides an unbalanced attenuator path referenced to ground. The balanced version is an H pad.
A pad can have equal or unequal input and output impedance.
To calculate the values for a pad, you must know the desired input impedance, output impedance and loss in dB.
To calculate the values for an H pad, first calculate the values for a T pad, and then divide the values of the input and output resistors (R1 and R2) in half to equally divide the load.
The value of loss in dB must be converted to a ratio of current, voltage or power. The formula to determine K is
K = 10(desired attenuation in dB/20)
Note: For all these formulae, Z and R values are expressed in ohms.
Equal Impedance Pad Calculation
The formulae to calculate a pad of equal input and output impedance is simplified because some of the values effectively cancel each other. Use the formulae in the next section to calculate values for pads with unequal impedances.
When Z1 equals Z2, R1 will equal R2.
Unequal Impedance Pad Calculation
The value of R3 can be used to determine the values of R1 and R2, so it is easier to calculate it first. The equation for R3 can be substituted in the equations for R1 and R2 if you prefer to repeat the work.
T and H pads are bidirectional, so either side can be used as the input. When calculating the values for a pad with unequal impedances, the value of Z1 must be greater than the value of Z2.
Acceptable Use Policy blog comments powered by Disqus
[an error occurred while processing this directive]
Today in Radio History
The history of radio broadcasting extends beyond the work of a few famous inventors.
Read each issue online in our Digital Edition Format in your Web browser.
EAS Information More on EAS
The feed provides feeds for all US states and territories.
Need a calendar for your computer desktop? Use one of ours.
Information from manufacturers and associations about industry news, products, technology and business announcements.
Staying on-air is priority #1, but 100 percent redundancy comes at a cost.
Browse Back Issues[an error occurred while processing this directive]
Also in the November Issue
- Music is Everywhere at WTMD
- FCC Looks to Update RF Exposure Rules
- Government Shutdown Causes FCC Delays
- Applied Technology: Wheatstone baseband192
- Side by Side: Video Cameras
- Exploring More from Google Earth
- The History of W9BSP