EP0157460A2
Expired / Lapsed
EP
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Closed circuit television system
Assignee: Philips Electronics UK Ltd
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Filing: 1985-04-02
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Granted: —
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Expires: 2005-04-02
Abstract
Abstract A closed circuit television system comprises a television camera (1), a frequency modulator (2), a series of lengths of transmission lines (3, 5, 7, 9, 11) forming a transmission path having correcting amplifiers (4, 6, 8, 19) at intervals along its length, a demodulator (12), and a television monitor (13). The transmission lines (3, 5, 7, 9, 11) are formed by balanced pair telephone conductors. One application of such a system is in monitoring conditions on motorways in the U.K. It is advantageous in this environment to be able to use the existing cables which are already installed along the length of the motorway system and by frequency modulating the video signal on a low frequency carrier so that the bandwidth of the frequency modulated signal lies between 1 and 5 MHz transmission of the signal over greater distances that previously possible can be achieved.
Inventors
- 👤 Alastair C/O Philips Business Systems Macarthur
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-24 12:11
CPC Classifications
H; H04; H04N; H04N7/00; H04N7/18; H04N7/183; H04N7/10; H04N7/108
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
93 words
A closed circuit television system comprising a television camera, a frequency modulator for frequency modulating the video signal produced by the camera, means for feeding the frequency modulated signal to one end of a transmission path which comprises balanced pair conductors provided with video correcting amplifiers at intervals along its length, and a demodulator for demodulating the signal received at the other end of the transmission path in which the demodulator includes a high-pass filter which is effective to reduce the amplitude of the lower sideband relative to that of the carrier signal.
Claim 2
Dependent Claim
93 words
A closed circuit television system comprising a television camera, a frequency modulator for frequency modulating the video signal produced by the camera, means for feeding the frequency modulated signal to one end of a transmission path which comprises balanced pair conductors provided with video correcting amplifiers at intervals along its length, and a demodulator for demodulating the signal received at the other end of the transmission path in which the demodulator includes a high-pass filter which is effective to reduce the amplitude of the lower sideband relative to that of the carrier signal.
Claim 3
Dependent Claim
22 words
A closed circuit television system as claimed in Claim 1 in which the cut-off frequency of the high pass filter is adjustable.
Claim 4
Dependent Claim
23 words
A closed circuit television system as claimed in Claim 1, in which the high-pass filter has a cut-off frequency of approximately 1 MHz.
Claim 5
Dependent Claim
44 words
A closed circuit television system as claimed in Claim 1, 2 or 3, in which a data channel is frequency division multiplexed with the video signal, the data channel occupying the area of the frequency spectrum below that of the frequency modulated video signal.
Claim 6
Dependent Claim
72 words
A closed circuit television system as claimed in any of Claims 1, 2, 3 or 4, in which the frequency demodulator includes a duplex limiter circuit which comprises first and second branches, the first branch comprising a low pass filter and the second branch comprising a high pass filter and a first limiting amplifier arranged in cascade, the first and second paths being combined at their outputs in a second limiting amplifier.
Claim 7
Dependent Claim
46 words
A closed circuit television system as claimed in any preceding claim, in which the modulator comprises a gain controlled amplifier the gain of which is reduced when the input video signal exceeds a preset level to prevent the output video signal from exceeding said preset level.
Claim 8
Dependent Claim
154 words
A closed circuit television system comprising a television camera, a television monitor, a transmission path linking the monitor and camera for transmitting video signals from the camera to the monitor, the transmission path comprising balanced pair conductors having correcting amplifiers at intervals along their length, means for frequency modulating the video signal produced by the camera so that frequencies below a given frequency are not transmitted, and means for transmitting control signals having frequencies below said given frequency from the television monitor or a position adjacent thereto to the telephone camera along the transmission path, in which at each correcting amplifier a bypass link is provided, said bypass link comprising a low pass filter having a cut off frequency below said given frequency and in which a high pass filter is provided at the input of each correcting amplifier to prevent said control signals from being applied to the input of the correcting amplifier.
Claim 9
Dependent Claim
154 words
A closed circuit television system comprising a television camera, a television monitor, a transmission path linking the monitor and camera for transmitting video signals from the camera to the monitor, the transmission path comprising balanced pair conductors having correcting amplifiers at intervals along their length, means for frequency modulating the video signal produced by the camera so that frequencies below a given frequency are not transmitted, and means for transmitting control signals having frequencies below said given frequency from the television monitor or a position adjacent thereto to the telephone camera along the transmission path, in which at each correcting amplifier a bypass link is provided, said bypass link comprising a low pass filter having a cut off frequency below said given frequency and in which a high pass filter is provided at the input of each correcting amplifier to prevent said control signals from being applied to the input of the correcting amplifier.
Claim 10
Dependent Claim
23 words
A closed circuit television system as claimed in Claim 7, in which the low pass filter has a cut off frequency below 100khz.
Claim 11
Dependent Claim
26 words
A closed circuit television system as claimed in Claim 7 or Claim 8, in which the high pass filter has a cut off frequency above 500Mhz.
References Cited (Backward Citations)
No citation records indexed.
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