Browse Prior Art Database

Reducing Differential Transformer Echo Return Loss

IP.com Disclosure Number: IPCOM000076339D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Peard, M: AUTHOR

Abstract

When connecting a four wire telephone set to a two wire transmission line TL through a hybrid transformer T1, any mismatching between the impedance of the transformer and that of the two-wire line, produces a loss of the signal transmitted towards the two-wire line. Since the line impedance depends on the location of the remote subscriber the two-wire line is connected to, a correction device developing a voltage opposed to the return voltage is provided when the local subscriber is in the transmitting mode.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 100% of the total text.

Page 1 of 2

Reducing Differential Transformer Echo Return Loss

When connecting a four wire telephone set to a two wire transmission line TL through a hybrid transformer T1, any mismatching between the impedance of the transformer and that of the two-wire line, produces a loss of the signal transmitted towards the two-wire line. Since the line impedance depends on the location of the remote subscriber the two-wire line is connected to, a correction device developing a voltage opposed to the return voltage is provided when the local subscriber is in the transmitting mode.

Assuming that transmitter E is in operation, while the remote subscriber is in the receiving mode, the larger the impedance mismatching is, the larger the echo return ER would be, unless the voltage: ER = EQ + ETR (where EQ is the balancing network R voltage, and ETR is the transformer T1 voltage), is applied in phase opposition onto the receiver transformer T2. As shown in the figure, this is done by means of amplifier A and transformer T3. The gain of A is equal to
0.9, so that the echo return loss is reduced to 20 dB. When E stops transmitting, the voltage EQ across the balancing network R drops to zero, so that the gain of amplifier A controlled by the output of level detector LD is set to zero. Thus the signal coming from the remote subscriber is not attenuated.

1

Page 2 of 2

2

[This page contains 1 picture or other non-text object]