US4007328A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Videotelephone system with anti-crosstalk means
Assignee: Italtel SpA
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Filing: 1974-09-30
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Granted: 1977-02-08
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Expires: 1994-09-30
Abstract
Abstract The outlying stations of a videotelephone system, adapted to communicate with one another through a central office, include each a video-reception section and a video-transmission section as well as an audio section provided with telephone equipment. A sync-pulse generator in the video-transmission section, comprising a crystal-controlled oscillator working into a pair of frequency dividers, controls the line-scan and frame-scan generators thereof as well as those of a remote station to which it is connected via an outgoing video line. A local sync-pulse extractor connected to an incoming video line controls the line-scan and frame-scan generators of the associated video-reception section. A switch enables replacement of the crystal-controlled oscillator with a variable-frequency oscillator locked in step with the sync-pulse generator of the remote station by the output of the local sync-pulse extractor whereby interference phenomena due to pick-up of incoming sync pulses, in random phase relationship with the locally generated sync pulses, are eliminated. The switchover to the variable-frequency oscillator may be carried out manually or, at a called station, by a detector circuit responsive to incoming audio or video signals, preferably to ringing current; the detector circuit includes a relay which locks for the duration of the established connection under the control of a hook switch.
Inventors
- 👤 Virgilio Mosca
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 23:10
CPC Classifications
H; H04; H04N; H04N7/00; H04N7/14; H04N7/141; H04N7/147
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
190 words
A videotelephone system with a plurality of stations adapted to enter into two-way communication with one another, each of said stations comprising: an audio section provided with telephone equipment; a video-transmission section including a television transmitter provided with a first frame-scan generator and a first line-scan generator; a video-reception section including a television receiver provided with a second frame-scan generator independent of said first frame-scan generator and a second line-scan generator independent of said first line-scan generator; a controllable sync-pulse source with output connections to said first line-scan and frame-scan generators and to an outgoing video line in a channel leading to a remote station temporarily communicating therewith; a sync-pulse extractor with input connections to an incoming line in said channel and with output connections to said second line-scan and frame-scan generators; and switchover means for operatively connecting said sync-pulse source to an output of said sync-pulse extractor to lock said first and second line-scan and frame-scan generators in step with one another for simultaneous transmission and reception of video signals with a common sync frequency upon establishment of communication with a remote station operating with a free-running sync-pulse source.
Claim 2
Dependent Claim
190 words
A videotelephone system with a plurality of stations adapted to enter into two-way communication with one another, each of said stations comprising: an audio section provided with telephone equipment; a video-transmission section including a television transmitter provided with a first frame-scan generator and a first line-scan generator; a video-reception section including a television receiver provided with a second frame-scan generator independent of said first frame-scan generator and a second line-scan generator independent of said first line-scan generator; a controllable sync-pulse source with output connections to said first line-scan and frame-scan generators and to an outgoing video line in a channel leading to a remote station temporarily communicating therewith; a sync-pulse extractor with input connections to an incoming line in said channel and with output connections to said second line-scan and frame-scan generators; and switchover means for operatively connecting said sync-pulse source to an output of said sync-pulse extractor to lock said first and second line-scan and frame-scan generators in step with one another for simultaneous transmission and reception of video signals with a common sync frequency upon establishment of communication with a remote station operating with a free-running sync-pulse source.
Claim 3
Dependent Claim
47 words
A system as defined in claim 1 wherein said sync-pulse source comprises oscillator means provided with a frequency-control circuit, said switchover meas having a first position deactivating said frequency-control circuit and a second position enabling said frequency-control circuit to adjust the operating frequency of said oscillator means.
Claim 4
Dependent Claim
55 words
A system as defined in claim 2 wherein said oscillator means comprises a fixed-frequency oscillator, a variable-frequency oscillator and frequency-dividing means alternately connectable by said switchover means to said fixed-frequency oscillator and to said variable-frequency oscillator in said first position and said second position, respectively, said variable-frequency oscillator being permanently connected to said frequency-control circuit.
Claim 5
Dependent Claim
27 words
A system as defined in claim 3 wherein said frequency-control circuit comprises a phase comparator with input connections to said sync-pulse extractor and to said frequency-dividing means.
Claim 6
Dependent Claim
32 words
A system as defined in claim 2, further comprising signal-responsive means connected to said channel for placing said switchover means in said second position upon initiation of communication by said remote station.
Claim 7
Dependent Claim
24 words
A system as defined in claim 5 wherein said signal-responsive means is connected to said telephone equipment for actuation by an incoming call signal.
Claim 8
Dependent Claim
55 words
A system as defined in claim 6 wherein said telephone equipment includes manual switch means manipulated by a user at the inception and the termination of a call, said signal-responsive means including holding means controlled by said switch means for maintaining said switchover means in said second position for the duration of an incoming call.
Claim 9
Dependent Claim
63 words
A system as defined in claim 7 wherein said channel includes a line loop connected to said telephone equipment, said holding means comprising a relay connected across said line loop in a normal position of said switch means for operation by said call signal and contacts coupled with said switch means and closed in an off-normal position thereof for keeping said relay operated.
Claim 10
Dependent Claim
65 words
A system as defined in claim 8 wherein said telephone equipment includes alarm means and a handset, said switch means being a hook switch actuated by said handset for normally disconnecting said line loop from said handset and connecting said line loop across said alarm means for monitoring call signals from a remote station, said relay having an energizing circuit connected across said alarm means.
Claim 11
Dependent Claim
42 words
A system as defined in claim 9 wherein said alarm means comprises a ringer responding to periodic bursts of alternating current, said energizing circuit including rectifying means for said alternating current and integrating means for keeping said relay energized between said bursts.
References Cited (Backward Citations)
US2206654A
Cited
US2757279A
Cited
US3311702A
Cited
US3263027A
Cited
US3723653A
Cited
US3873771A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1980-02-08 | 1980-08-09 | 1981-02-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-02-08 | 1984-08-09 | 1985-02-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-02-08 | 1988-08-09 | 1989-02-08 | $7700.00 | Window Closed / Lapsed |