Balanced Attenuator Calculator (H-Pad)
Design symmetrical H-Pads for balanced audio lines (600Ω) or differential RF pairs.
Balanced Pad Types
Engineering Principles: Balanced Attenuator (H-Pad)
A Balanced Attenuator (often called an H-Pad) is used in balanced transmission lines (like 600Ω audio or differential RF) where both conductors carry signal relative to ground. It maintains symmetry and impedance matching for both lines.
Standard T-pad series R divided by 2. (Where K=10^(dB/20)).
Single resistor bridging the two lines.
Rejection of common-mode noise (CMRR) is preserved.
Technical Notes
- •In an H-pad, there are 4 series resistors (2 top, 2 bottom) and 1 shunt resistor? Or typically 2 series (1 top, 1 bottom) and 1 shunt? Standard H-pad has 1 series resistor per leg side (Input/Output).
- •The calculator assumes a symmetric H-Pad topology (Balanced T).
- •For an O-Pad (Balanced Pi), formulas would differ.
Frequently Asked Questions
What is an H-Pad Attenuator?
An H-Pad is the balanced version of a T-Pad attenuator. It distributes the series resistance equally between the top and bottom conductors to strictly maintain the symmetry and Common Mode Rejection Ratio (CMRR) of the balanced transmission line.
Why use balanced lines?
Balanced lines (like Twisted Pair or 600Ω audio lines) are immune to external electromagnetic interference (EMI) because any noise induced on the line affects both conductors equally and is cancelled out by the differential receiver.
What is the difference between H-Pad and O-Pad?
An H-Pad is a balanced T-Network (Series-Shunt-Series). An O-Pad is a balanced Pi-Network (Shunt-Series-Shunt). H-Pads are often preferred for variable attenuators, while O-Pads may be used when specific resistor values are easier to achieve with that topology.