Patent US3985976A successfully refreshed from Google Patents.
US3985976A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Audio frequency signalling systems for telephone systems
Assignee: Individual
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Filing: 1975-02-10
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Granted: 1976-10-12
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Expires: 1995-02-10
Abstract
Abstract Audio frequency signalling, from a central location in a telephone system to a remote location serviced by a particular telephone set, is accomplished by connecting an audio frequency amplifier, having a predetermined a.c. threshold voltage level, and a predetermined d.c. voltage level, across the telephone line at said particular telephone set. By concurrently applying a low frequency a.c. pilot signal of an amplitude greater than the a.c. threshold voltage level of the audio frequency amplifier and an audio frequency signal voltage of a lesser amplitude to the telephone line at the central location, when said particular telephone set is on-hook, said audio frequency amplifier is enabled by the low frequency a.c. pilot signal and supplied with operating current from the telephone line. The audio frequency amplifier, thus enabled and energized, attenuates the low frequency a.c. pilot signal and amplifies the audio frequency signal voltage to produce a corresponding audible signal at a loudspeaker coupled to said audio frequency amplifier. When the handset of said particular telephone set is taken off-hook the d.c. voltage across the telephone line at said particular telephone set drops below the predetermined d.c. threshold voltage level to disable said audio frequency amplifier.
Inventors
- 👤 Michael Christopher John Cowpland
- 👤 Terrance Headley Matthews
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 14:26
CPC Classifications
H; H04; H04M; H04M9/00; H04M9/001; H04M11/00; H04M11/02; H04M19/00; H04M19/02; H04M19/04
Claims Analysis
Total Claims: 31
Claim 1
Independent Claim
145 words
In combination with an amplifier for connection to a transmission line, the improvement comprising: a. means responsive to a predetermined a.c. voltage and a d.c. voltage carried by the transmission line for applying said a.c. voltage to said amplifier in the event said a.c. voltage has an amplitude above a first predetermined amplitude threshold and for generating an enabling voltage in the event said a.c. voltage has an amplitude above a first predetermined amplitude threshold and said d.c. voltage has an amplitude above a second predetermined amplitude threshold; b. means responsive to the presence of said enabling voltage for enabling said amplifier by applying said d.c. voltage as a power supply to said amplifier; and c. means for inhibiting translation of said predetermined a.c. voltage by the enabled amplifier, while allowing translation of other audio frequency signals which may be present on the transmission line.
Claim 2
Dependent Claim
145 words
In combination with an amplifier for connection to a transmission line, the improvement comprising: a. means responsive to a predetermined a.c. voltage and a d.c. voltage carried by the transmission line for applying said a.c. voltage to said amplifier in the event said a.c. voltage has an amplitude above a first predetermined amplitude threshold and for generating an enabling voltage in the event said a.c. voltage has an amplitude above a first predetermined amplitude threshold and said d.c. voltage has an amplitude above a second predetermined amplitude threshold; b. means responsive to the presence of said enabling voltage for enabling said amplifier by applying said d.c. voltage as a power supply to said amplifier; and c. means for inhibiting translation of said predetermined a.c. voltage by the enabled amplifier, while allowing translation of other audio frequency signals which may be present on the transmission line.
Claim 3
Dependent Claim
48 words
The combination as defined in claim 1, wherein said means responsive to the presence of a d.c. voltage includes means for applying said d.c. voltage from the transmission line to the amplifier only upon the d.c. voltage exceeding the amplifier d.c. voltage threshold for powering the amplifier therefrom.
Claim 4
Dependent Claim
122 words
In combination with an amplifier for connection to a telephone type line, the improvement comprising: a. means for sensing a d.c. voltage above a first threshold level carried by the telephone line, b. means for sensing a predetermined a.c. voltage above a second threshold level carried by the telephone line, c. means for enabling said amplifier to amplify message signals received from the telephone line only when the amplitude of both the d.c. voltage and the a.c. voltage exceed the respective first and second threshold levels said amplifying means being inhibited in the event either of said voltages has less amplitude than their respectivve threshold levels, and d. means for preventing translation of said a.c. voltage to the output of said amplifier.
Claim 5
Dependent Claim
122 words
In combination with an amplifier for connection to a telephone type line, the improvement comprising: a. means for sensing a d.c. voltage above a first threshold level carried by the telephone line, b. means for sensing a predetermined a.c. voltage above a second threshold level carried by the telephone line, c. means for enabling said amplifier to amplify message signals received from the telephone line only when the amplitude of both the d.c. voltage and the a.c. voltage exceed the respective first and second threshold levels said amplifying means being inhibited in the event either of said voltages has less amplitude than their respectivve threshold levels, and d. means for preventing translation of said a.c. voltage to the output of said amplifier.
Claim 6
Dependent Claim
80 words
The combination as defined in claim 3, wherein said means for preventing translation of the a.c. voltage to the output of said amplifier comprises a capacitor connected between the input of said amplifier and ground so that said a.c. voltage is suppressed in the event both the amplitudes of the d.c. voltage and a.c. voltage are greater than their respective threshold levels but at the same time permitting said message signals to be applied by the line to said amplifier.
Claim 7
Dependent Claim
18 words
The combination as defined in claim 4, in which said a.c. voltage is comprised of a pilot tone.
Claim 8
Dependent Claim
16 words
The combination as defined in claim 4, in which said a.c. voltage is of subaudible frequency.
Claim 9
Dependent Claim
35 words
The combination as defined in claim 6, in which said amplifier is connected to a transducer which comprises a loudspeaker, adapted to receive audio frequency tones and voice messages as message signals from the line.
Claim 10
Dependent Claim
37 words
The combination as defined in claim 3, in which the means for amplifying an a.c. voltage comprises means for discriminating all a.c. voltage frequencies below a predefined frequency and for amplifying only frequencies above the predefined frequency.
Claim 11
Dependent Claim
39 words
The combination as defined in claim 3, in which said first threshold level for said d.c. voltage is greater than the voltage appearing across a busy telephone line, and less than the voltage appearing across an idle telephone line.
Claim 12
Dependent Claim
41 words
The combination as defined in claim 3, wherein said enabling means includes means for applying the d.c. voltage appearing on said line as power supply current for energizing the amplifier only when said d.c. voltage exceeds the amplifier d.c. voltage threshold.
Claim 13
Dependent Claim
125 words
An amplifier for connection to a transmission line comprising: a. first means for detecting a first enabling d.c. voltage above a prescribed first threshold level, b. second means responsive to said first means for detecting a second enabling a.c. voltage above a prescribed second threshold level, c. means for amplifying a signal different from said a.c. voltage or said d.c. voltage appearing on said line upon detection of both the d.c. and a.c. voltage levels by said first and second means in excess of the respective first and second threshold levels, including means for barring said amplification in the event either of the d.c. or a.c. voltage levels are less than the respective thresholds, and d. means for preventing amplification of said enabling a.c. voltage.
Claim 14
Dependent Claim
125 words
An amplifier for connection to a transmission line comprising: a. first means for detecting a first enabling d.c. voltage above a prescribed first threshold level, b. second means responsive to said first means for detecting a second enabling a.c. voltage above a prescribed second threshold level, c. means for amplifying a signal different from said a.c. voltage or said d.c. voltage appearing on said line upon detection of both the d.c. and a.c. voltage levels by said first and second means in excess of the respective first and second threshold levels, including means for barring said amplification in the event either of the d.c. or a.c. voltage levels are less than the respective thresholds, and d. means for preventing amplification of said enabling a.c. voltage.
Claim 15
Dependent Claim
118 words
In combination with an amplifier for connection to a transmission line, the improvement comprising: a. means for sensing the presence of a d.c. voltage carried by the transmission line, and for providing an enabling voltage in the event the d.c. voltage is above a predetermined amplitude threshold, b. means enabled by said enabling voltage for sensing a predetermined a.c. voltage carried by the transmission line, and for enabling operation of said amplifier in the event said a.c. voltage has an amplitude above a second predetermined amplitude threshold, and c. means for inhibiting translation of said predetermined a.c. voltage by the enabled amplifier, while allowing translation of other audio frequency signals which may be present on the transmission line.
Claim 16
Dependent Claim
118 words
In combination with an amplifier for connection to a transmission line, the improvement comprising: a. means for sensing the presence of a d.c. voltage carried by the transmission line, and for providing an enabling voltage in the event the d.c. voltage is above a predetermined amplitude threshold, b. means enabled by said enabling voltage for sensing a predetermined a.c. voltage carried by the transmission line, and for enabling operation of said amplifier in the event said a.c. voltage has an amplitude above a second predetermined amplitude threshold, and c. means for inhibiting translation of said predetermined a.c. voltage by the enabled amplifier, while allowing translation of other audio frequency signals which may be present on the transmission line.
Claim 17
Dependent Claim
41 words
An amplifier as defined in claim 12, wherein said enabling means includes means for applying direct current from the transmission line to the signal amplifier upon the d.c. voltage exceeding the amplifier d.c. voltage threshold for powering the signal amplifier therefrom.
Claim 18
Dependent Claim
119 words
In combination with an amplifier for connection to a telephone type line, the improvement comprising: a. first means for sensing a d.c. voltage above a first threshold level carried by the line, b. second means for sensing a predetermined a.c. voltage above a second threshold level carried by the line, c. means for enabling operation of said amplifier to amplify message signals different than said a.c. voltage carried by the line in the event the amplitude of both the d.c. voltage and said a.c. voltage exceed the respective first and second threshold levels, and for inhibiting operation of the amplifier in the event either the d.c. voltage or said a.c. voltage has less amplitude than their respective threshold levels.
Claim 19
Dependent Claim
119 words
In combination with an amplifier for connection to a telephone type line, the improvement comprising: a. first means for sensing a d.c. voltage above a first threshold level carried by the line, b. second means for sensing a predetermined a.c. voltage above a second threshold level carried by the line, c. means for enabling operation of said amplifier to amplify message signals different than said a.c. voltage carried by the line in the event the amplitude of both the d.c. voltage and said a.c. voltage exceed the respective first and second threshold levels, and for inhibiting operation of the amplifier in the event either the d.c. voltage or said a.c. voltage has less amplitude than their respective threshold levels.
Claim 20
Dependent Claim
58 words
The combination as defined in claim 14, including means for suppressing amplification in the amplifier of said a.c. voltage in the event both the amplitudes of the d.c. voltage and the a.c. voltage are greater than their respective said threshold levels, but at the same time for amplifying said message signals which may be carried by the line.
Claim 21
Dependent Claim
18 words
The combination as defined in claim 15, in which said a.c. voltage is comprised of a pilot tone.
Claim 22
Dependent Claim
16 words
The combination as defined in claim 15, in which said a.c. voltage is of subaudible frequency.
Claim 23
Dependent Claim
30 words
The combination as defined in claim 17, further including an electro-acoustic transducer coupled to the output of the amplifier for reproducing audio frequency signals as message signals from the line.
Claim 24
Dependent Claim
50 words
The combination as defined in claim 14, in which the means for enabling operation of said amplifier comprises means for discriminating all a.c. voltage frequencies below a predefined frequency and for amplifying only frequencies above the predetermined frequency, the frequency of the predetermined a.c. voltage being below the predefined frequency.
Claim 25
Dependent Claim
39 words
The combination as defined in claim 14, in which said predetermined threshold for d.c. voltage is greater than the d.c. voltage appearing across a busy telephone line, and less than the d.c. voltage appearing across an idle telephone line.
Claim 26
Dependent Claim
29 words
The combination as defined in claim 14, wherein said enabling means includes means for applying direct current appearing on the line as power supply current for energizing the amplifier.
Claim 27
Dependent Claim
104 words
In combination with an amplifier for connection to a transmission line, the improvement comprising: a. means establishing a first enabling d.c. voltage threshold level, b. means establishing a second enabling a.c. voltage threshold level, c. means for translation of a separate message signal appearing on said line by said amplifier upon receipt by said amplifier of both d.c. and a.c. enabling voltages in excess of the respective threshold levels, for barring translation of the a.c. enabling voltage, and for barring translation of the separate message signal in the event either of the d.c. or a.c. enabling voltages are less than the respective threshold levels.
Claim 28
Dependent Claim
104 words
In combination with an amplifier for connection to a transmission line, the improvement comprising: a. means establishing a first enabling d.c. voltage threshold level, b. means establishing a second enabling a.c. voltage threshold level, c. means for translation of a separate message signal appearing on said line by said amplifier upon receipt by said amplifier of both d.c. and a.c. enabling voltages in excess of the respective threshold levels, for barring translation of the a.c. enabling voltage, and for barring translation of the separate message signal in the event either of the d.c. or a.c. enabling voltages are less than the respective threshold levels.
Claim 29
Dependent Claim
26 words
The combination as defined in claim 22, in which the amplifier comprises means for amplifying only said message signals which are above a predetermined frequency range.
Claim 30
Dependent Claim
53 words
The combination as defined in claim 23, in which the amplifier is a differential amplifier, further including means for applying alternating current signals below said predetermined frequency range in phase to said amplifier whereby they are canceled, and for applying alternating current signals above said predetermined frequency range differentially whereby they are amplified.
Claim 31
Dependent Claim
65 words
The combination as defined in claim 24, including means for applying alternating frequency signals to two inputs of said differential amplifier in phase, and for bypassing alternating frequency signals above said predetermined frequency range from one of the inputs to provide a differential signal whereby said differential signal, representative of the alternating frequency signal above said predetermined frequency range, is amplified by the differential amplifier.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-10-12 | 1980-04-12 | 1980-10-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-10-12 | 1984-04-12 | 1984-10-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-10-12 | 1988-04-12 | 1988-10-12 | $7700.00 | Window Closed / Lapsed |