Browse Prior Art Database

Echo Protection for Multifrequency Receiver

IP.com Disclosure Number: IPCOM000046841D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Ballatore, D: AUTHOR [+2]

Abstract

The echo protection circuit shown in the drawing is to be used in multifrequency receivers (MFRs) for protecting the receivers against echo, without degrading voice protection. The circuit is shown in Fig. 1A, and the timing is shown in Fig. 1B. The multifrequency (MF) signal is comprised of two frequencies A and B which are separated by filters. Frequencies A are the low range frequencies, and frequencies B are the high range frequencies. The echo protection circuit has two operating modes: normal and hold. In the normal mode, the frequency B signal is applied to a single-wave rectifier comprising amplifier A1 and diode D which provides a voltage VC3 with a time constant T3 = (R31$R32/R31+R32) $ C3 and an amplitude which is equal to two-thirds of the envelope amplitude of the MF signal.

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 66% of the total text.

Page 1 of 2

Echo Protection for Multifrequency Receiver

The echo protection circuit shown in the drawing is to be used in multifrequency receivers (MFRs) for protecting the receivers against echo, without degrading voice protection. The circuit is shown in Fig. 1A, and the timing is shown in Fig. 1B. The multifrequency (MF) signal is comprised of two frequencies A and B which are separated by filters. Frequencies A are the low range frequencies, and frequencies B are the high range frequencies. The echo protection circuit has two operating modes: normal and hold. In the normal mode, the frequency B signal is applied to a single-wave rectifier comprising amplifier A1 and diode D which provides a voltage VC3 with a time constant T3 = (R31$R32/R31+R32) $ C3 and an amplitude which is equal to two-thirds of the envelope amplitude of the MF signal. The frequency B signal is chosen instead of the frequency A signal since a higher frequency difference between the fundamental frequency and amplitude fluctuation frequency makes the filtering easier. The single-wave rectifier gives also the complete envelope amplitude VC4 with a time constant T4 = R4C4, which is lower than T3. So VC3 < VC4 in the normal mode, the output signal of amplifier A2 is high, and the MFR filter B is enabled. After a check period, the MFR detects that the MF signal is valid and the delayed steering output STD goes up at time t1, and the voltage VC3 is hold at its value at time t1. In hold mode, VC4 has approxim...