# ABCD Parameters

The ABCD parameters of generalized constant of the transmission line is find out by sending end current and sending end voltage equation. In order to find out ABCD parameters of the transmission line, it is considered that (1) The receiving end of the transmission line is open circuited and (2) Receiving end of the transmission line is short circuited.

VS = AVR + BIR

IS = CVR + DIR

Where

VS = Sending end voltage

IS = Sending end current

VR = Receiving end voltage

IR = Receiving end current

A, B, C and D = Constant

The generalized constant of the transmission line is found out by

Receiving end of the transmission line open circuited, receiving end current IR = 0

## ABCD Parameters: Receiving End Open Circuited

Constant A

VS = AVR

A = VS / VR and

The constant A is defined as the ratio of sending end voltage to the receiving end voltage when receiving end of the line is open circuited. It is also called as reverse voltage gain. It is unitless.

Constant C

IS = CVR

C = IS / VR

The constant C is defined as the ratio of sending end current to the receiving end voltage when receiving end of the line is open circuited. Its unit is 1 / ohm or mho.

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Receiving end of the transmission line is short circuited, when receiving end voltage VR = 0

## ABCD Parameters: Receiving End Short Circuited

Constant B

VS = BIR

B = VS / IR

The constant B is defined as the ratio of sending end voltage to the receiving end current when receiving end of the transmission line is short circuited. Its unit is ohm.

Constant D

IS = DIR

D = IS / IR

The constant D is defined as the ratio of sending end current to the receiving end current when receiving end of the transmission line is short circuited. It is also called as reverse current gain. It is unit less.

## ABCD Parameters: Summary

 Transmission line parameters How to Find out? Formula Unit Better known as A Receiving end of transmission line is open circuited VS / VR Unit less Reverse voltage gain B Receiving end of transmission line is short circuited VS / IR ohm C Receiving end of transmission line is open circuited IS / VR mho D Receiving end of transmission line is short circuited IS / IR Unit less Reverse current gain