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The hybrid circuit summarized
nThe hybrid circuit transforms two-wire connection into 4-wire
connection.
nIf the hybrid is unbalanced echo will result
nHybrid is balanced when no own voice is leaked into own
loudspeaker
nHybrid unbalance can result from line impedance changes due to
weather conditions
nUnbalance results echo
nEcho cancellation
circuits are harmful in data connections
nNowadays realized by operational amplifier based circuitry that automatically monitors line
impedance changes