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Echo Return Loss Compensation by Switched Files

IP.com Disclosure Number: IPCOM000088257D
Original Publication Date: 1977-May-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Peard, M: AUTHOR

Abstract

Compensation for echo return loss in a duplex transmission is provided here by combining adjustments on balancing impedance with compensation in the frequency domain.

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Echo Return Loss Compensation by Switched Files

Compensation for echo return loss in a duplex transmission is provided here by combining adjustments on balancing impedance with compensation in the frequency domain.

Conventional duplex transmission usually uses a two-to-four wire conversion to separate receiving and transmitting paths from each other. The basic arrangement of a terminal station includes, therefore, a hybrid transformer T connected, on one side, to the line L and, on the other side, to the separate paths going through amplifiers A1 and A2. Due to the high input and low output impedance characteristics of these amplifiers, the resistors R(1) and R(2) are used for matching purposes.

This circuit is balanced by adjusting a network ZB connected between the center tap of the transformer and ground. This network comprises two series- connected cells, the impedances of which are equivalent to the impedance of the terminal connected to the line and the impedance of the line itself, respectively, both reflected to the primary of the transformer. Balancing is achieved by tuning these two cells to minimize the current flowing through ZB.

The tuning of ZB is achieved through the use of switched filters. Four low- level preset frequencies, i.e., 300, 650, 1400 and 3000 Hz, are fed to the transmitter amplifier. On the return path, i.e., at the input of the receiving amplifier, a bank of four high Q switched filters is tuned to these preset frequencies. Each filt...