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Measuring Group Delay

IP.com Disclosure Number: IPCOM000075254D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Couder, AA: AUTHOR

Abstract

This description is directed to a method for measuring group delay through a transmission medium and more particularly, to such a method performed by a computer.

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This is the abbreviated version, containing approximately 99% of the total text.

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Measuring Group Delay

This description is directed to a method for measuring group delay through a transmission medium and more particularly, to such a method performed by a computer.

This method uses the Nyquist and Brand's principle. According to this principle, the group delay of an amplitude-modulated signal passing through a transmission medium, is proportional to the phase shift of the signal envelope.

The group delay of a transmitted reference tone is used as group-delay reference, and permits measurement of relative group delay for different frequencies.

The amplitude-modulated transmitted reference tone and the amplitude- modulated frequency to be measured are sequentially emitted through the transmission medium. The program of the computer is so designed that no discontinuity appears on the envelope between the two emitted frequencies.

On reception, in order to reduce computing time, the extraction of the envelope of the received signal is achieved by rectification, i.e. by taking the absolute value of the received signal.

The phase shift between the envelope of the received signal to be measured, and a reference envelope within the receiver, and the phase shift between the envelope of the received reference tone and the reference envelope permits measurement of the relative group delay of the signal to be measured with respect to the reference tone.

This measurement is performed by the computer using the Discrete Fourier Transform in a straight forward...