Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1990-12-03
1992-08-11
Groody, James J.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358189, 455 66, H04N 538, H04N 540
Patent
active
051384566
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention has for its object processes for transmitting video signals from a video camera to a television set, video cameras for carrying out these processes and applications of these cameras.
The technical sector of the invention is that of the construction of static video cameras intended in particular for watching or for local uses, or of mobile cameras.
In numerous applications such as the watching of premises, stores, banks, appartments, etc . . . , fixed cameras are used, distributed in the premises, which transmit signals to video monitors located in a watching station.
Transmission of the signals between the cameras and the video monitors is generally effected by cables in order not to disturb reception of the public television broadcasts which are transmitted by Hertzian waves on determined channels.
Exceptionally, the authorities in charge of controlling use of the carrier frequencies may allow a local transmission by Hertzian waves on a well-determined carrier frequency, which is free in the emission zone, but such authorizations are difficult to obtain and cannot be multiplied.
The development of technologies makes it possible at the present time to construct video cameras for watching having very good performances for a reduced cost.
However, the transmission of the signals by cables between the camera and the video monitors involves considerable expenses and limits the applications of the watching cameras.
SUMMARY OF THE INVENTION
The object of the present invention is to provide means for transmitting by Hertzian waves the video signals issuing from a camera without disturbing the public television broadcasts or other transmission by Hertzian waves already in service in the signal transmission zone and, consequently, making it possible to avoid the construction costs of the signal transmission lines and to receive the images coming from a watching camera directly on television sets or on existing video monitors.
This object is attained by a process for transmitting by Hertzian waves video signals from a video camera, which comprises the following operations of: automatically detecting the carrier frequencies of video signals which are already occupied in the zone of use of the camera and transmitting the video signals issuing from the camera, by mixing them, at a free carrier frequency which is different from a multiple or a sub-multiple of the occupied frequencies.
According to a preferred embodiment, the carrier frequencies of video signals which are already occupied locally are detected by means of a tuner which is connected to a transceiver antenna and which scans the whole of the range of carrier frequencies, and a detection circuit which detects the resonance peaks; there are recorded in the memory of a calculating unit the values of the occupied frequencies, corresponding to said resonance peaks and said calculating unit is programmed to select an available carrier frequency located substantially in the middle of the largest interval between two occupied frequencies and different from a multiple or a sub-multiple of the occupied frequencies and said calculating unit controls emission by a local oscillator of a carrier frequency which corresponds to said available frequency.
A video camera according to the invention comprises: with a tuning detector circuit which detects the occupied frequencies; which controls scanning of said tuner, which records the occupied frequencies and which is programmed to select a free frequency located substantially in the middle of the largest interval between two occupied frequencies and different from a multiple or a sub-multiple of one of the occupied frequencies and to control the emission by said oscillator of a carrier frequency which corresponds to said free frequency.
A camera according to the invention preferably comprises, in addition, a display device which displays the frequency selected.
The invention results in novel video cameras adapted to be used for local image transmissions, for example as watc
REFERENCES:
patent: 4213152 (1980-07-01), Kakinuma
patent: 4263617 (1981-04-01), Chemin et al.
patent: 4571621 (1986-02-01), Dalimonte et al.
patent: 4794458 (1988-12-01), Nagatomi
patent: 4916532 (1990-04-01), Streck et al.
Burgess Glenton B.
Groody James J.
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