Browse Prior Art Database

Specific Frequencies Signal Detector

IP.com Disclosure Number: IPCOM000084838D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Godard, D: AUTHOR

Abstract

This detecting circuit is capable of selectively detecting specific frequency signals present in a transmission frequency band. The drawings illustrate such a detecting circuit assuming the specific frequency signals to be detected has two frequency components f(1) and f(2).

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 65% of the total text.

Page 1 of 2

Specific Frequencies Signal Detector

This detecting circuit is capable of selectively detecting specific frequency signals present in a transmission frequency band. The drawings illustrate such a detecting circuit assuming the specific frequency signals to be detected has two frequency components f(1) and f(2).

Referring to Fig. 1, notch filters F1 and F2 cancel the frequency components f1 and f2 of the input signal, respectively. The output of F2 is applied to the two inputs of multiplier M1 whose output is applied to the input of integrator I1. the output of I1 provides the energy E/2/ out of the output signal from F2. The input signal is also applied to a second path comprising a delay element D provided for compensating for the delay introduced by filters F1 and F2, multiplier M3, and integrator 12. The output of I2 provides the energy E/2/ in of the input signal.

The output energy E/2/ out is always proportional to noise energy sigma /2/ regardless of the input signal. E/2/ out = alpha sigma/2/, the constant of proportionality alpha depending on the transfer function of filters F1 and F2. Assuming E/2/(S) is the energy of the signal to be detected, the input energy is: E/2/in = sigma/2/ when only noise is received; E/2/in = E/2/(S) + sigma/2/ when the signal to be detected is received.

Detection of the specific frequencies signal occurs when E/2/ in exceeds a threshold value comprised between sigma/2/ and E/2/s + sigma/2/. This threshold value is chosen equa...